KINKEN
Research Highlights
2022

Institute for Materials Research, Tohoku University

KINKEN Research Highlights 2022
Contents
Preface���������������������������������������������������������������������������������������������������������������������������������������������������������� 4
Research Highlights
1. Infrastructural Materials
Microstructure Design of Structural Metallic Materials Research Laboratory���������������������������������������������� 8
Irradiation Effects in Nuclear and Their Related Materials Research Laboratory����������������������������������������� 9
Environmentally Robust Materials Research Laboratory���������������������������������������������������������������������������� 10
Advanced Crystal Engineering Research Laboratory���������������������������������������������������������������������������������11
Non-Equilibrium Materials Research Laboratory���������������������������������������������������������������������������������������� 12
Deformation Processing Research Laboratory������������������������������������������������������������������������������������������ 13
Analytical Science Research Laboratory��������������������������������������������������������������������������������������������������� 14
Design & Engineering by Joint Inverse Innovation for Materials Architecture (DEJI2MA)�������������������������� 15
Professional development Consortium for Computational Materials Scientists (PCoMS)�������������������������� 16

2. Energy-Related Materials
Materials Design by Computer Simulation Research Laboratory��������������������������������������������������������������� 18
Nuclear Materials Engineering Research Laboratory�������������������������������������������������������������������������������� 19
Chemical Physics of Non-Crystalline Materials Research Laboratory������������������������������������������������������� 20
Structure-Controlled Functional Materials Research Laboratory��������������������������������������������������������������� 21
Magnetic Materials Research Laboratory�������������������������������������������������������������������������������������������������� 22
Hydrogen Functional Materials Research Laboratory�������������������������������������������������������������������������������� 23

3. Electronic Materials
Theory of Solid State Physics Research Laboratory���������������������������������������������������������������������������������� 26
Crystal Physics Research Laboratory�������������������������������������������������������������������������������������������������������� 27
Magnetism Research Laboratory��������������������������������������������������������������������������������������������������������������� 28
Low Temperature Physics Research Laboratory���������������������������������������������������������������������������������������� 29
Low Temperature Condensed State Physics Research Laboratory����������������������������������������������������������� 30
Quantum Beam Materials Physics Research Laboratory��������������������������������������������������������������������������� 31
Quantum Functional Materials Physics Research Laboratory�������������������������������������������������������������������� 32
Solid-State Metal-Complex Chemistry Research Laboratory��������������������������������������������������������������������� 33

Crystal Chemistry Research Laboratory���������������������������������������������������������������������������������������������������� 34
Actinide Materials Science Research Laboratory�������������������������������������������������������������������������������������� 35
Materials Science of Non-Stoichiometric Compounds Research Laboratory�������������������������������������������� 36
Exploratory Research Laboratory�������������������������������������������������������������������������������������������������������������� 37

Research Centers
International Research Center for Nuclear Materials Science�������������������������������������������������������������������� 40
Cooperative Research and Development Center for Advanced Materials������������������������������������������������ 41
High Field Laboratory for Superconducting Materials�������������������������������������������������������������������������������� 42
Trans-Regional Corporation Center for Industrial Materials Research������������������������������������������������������� 43
Collaborative Research Center on Energy Materials���������������������������������������������������������������������������������� 44
Center for Computational Materials Science���������������������������������������������������������������������������������������������� 45
Center of Neutron Science for Advanced Materials����������������������������������������������������������������������������������� 46
International Collaboration Center (ICC-IMR)��������������������������������������������������������������������������������������������� 47
Center for Advanced Light Source and Materials Science������������������������������������������������������������������������ 48
Laboratory of Low Temperature Materials Science������������������������������������������������������������������������������������ 49
Laboratory of Alpha-Ray Emitters�������������������������������������������������������������������������������������������������������������� 50
Analytical Research Core for Advanced Materials������������������������������������������������������������������������������������� 51

International Collaborative Research
Magnetism Research Laboratory��������������������������������������������������������������������������������������������������������������� 54
Microstructure Design of Structural Metallic Materials Research Laboratory�������������������������������������������� 55
Advanced Crystal Engineering Research Laboratory�������������������������������������������������������������������������������� 56
Non-Equilibrium Materials Research Laboratory���������������������������������������������������������������������������������������� 57
Magnetic Materials Research Laboratory�������������������������������������������������������������������������������������������������� 58
International Research Center for Nuclear Materials Science�������������������������������������������������������������������� 59
Cooperative Research and Development Center for Advanced Materials������������������������������������������������ 60
High Field Laboratory for Superconducting Materials�������������������������������������������������������������������������������� 61
Center for Computational Materials Science���������������������������������������������������������������������������������������������� 62
Center of Neutron Science for Advanced Materials����������������������������������������������������������������������������������� 63

Preface

Dear Colleagues,

We are pleased to present KINKEN Research Highlights 2022, which is the annual report that
includes a collection of research outputs of the past year from the Institute for Materials Research (IMR),
Tohoku University. KINKEN is the abbreviation for “Kinzoku Zairyo Kenkyujo,” the Japanese name for
IMR, which is well known in the materials science community.

IMR was the first Tohoku University research institute, of which there are currently six, to beestablished in 1916. Aiming to contribute to the well-being of the human race and the development ofcivilization through the creation of new materials that are useful to society, it carries out research on boththe fundamentals and applications of a wide range of substances and materials. After its founding, IMR
first focused on steel but quickly expanded its research area to the other metals and alloys. Then, in
response to changing times and economic growth, it came to cover semiconductors, ceramics, and awide range of other materials. Ever since our first director, Professor Kotaro Honda, invented the first
artificial permanent magnet called “KS steel,” we have developed many new materials for practical use,
including Sendust alloy, SiC fibers, and soft magnetic amorphous alloys. We have also focused on
fundamental research, which is important for the development of new materials, as well as carried out
cutting-edge research on magnetism, optical properties, superconductivity, and microstructure ofmaterials. While doing so, IMR has become a leading research institute in the field of materials science.

IMR is notable for its fusion of fundamental and applied research, as well as of science andengineering. We offer some of the best large research facilities in the world — covering high-energy

4

IMR KINKEN Research Highlights 2022

Director Prof. Tadashi Furuhara

irradiation, strong magnetic fields, and supercomputing — enabling researchers from Japan and abroad
to engage in a variety of collaborative projects. To develop superior or new materials that are useful, we
believe it is necessary to organically connect three “pillars”: (1) the “exploration” of physical phenomenathat govern materials’ functions, (2) the “creation” of materials via various methods, and (3) the“measurement” of materials’ properties from various perspectives. IMR has for many years been
contributing to the materials research community via our joint usage/research programs. IMR celebrated
its 100-year anniversary in 2016. Having been designated in 2018 as an International Joint Usage/
Research Center in Materials Science, known as Global Institute for Materials Research Tohoku (GIMRT),
we have now further heightened our efforts to enhance such collaborations and cultivate new talent.

In the 21st century, our society faces global-scale environmental issues, such as global warming,
resource depletion, acquiring a stable energy supply, and new kinds of environmental pollution. IMR willcontinue to work towards a sustainable society both by engaging in important research to solve various
problems as well as by creating new areas of research that can bring about paradigm shifts in the future.

We hope that the KINKEN Research Highlights will enable you to better understand our recent
research activities and will aid the promotion of worldwide collaboration with IMR. We ask for yourcontinued support and welcome any suggestions.

IMR KINKEN Research Highlights 2022

5

Infrastructural Materials

IMR KINKEN Research Highlights 2022

Research

Infrastructural Materials

Ferrite Transformation in Fe-0.3N AlloyF

errite transformation behavior during isothermal holding was studied in the ferrite (α) + austenite (γ) two-phaseregion of Fe-0.3mass%N binary alloy. Two morphologies of Allotoriomorphic ferrite (AF) and Widmanstetten
ferrite (WF) formed from the prior γ grain boundary. The retained γ was obtained by decreasing the transformation
temperature in the two-phase region, and a maximum volume fraction of 9% was obtained by holding at 600 °C.
AF had a near Kurdjumov-Sachs orientation relationship (K-S OR) with one side of the adjacent γ grains andgrew into the γ grains without K-S OR. On the other hand, WF had a near K-S OR with the matrix.
(b)

(a)

AF

γ(M)

20 μm

(c)

20 μm
(d)
WF

WF
MA

MA

20 μm

IMR KINKEN Research Highlights 2022

20 μm

Fig. 1 Microstructures of isothermally treated samples. (a) 5s and (b)3600 s at 750 oC, (c) 5 s and (d) 3600 s at 600
oC, respectively [4].
(a)

(b)

100

100

Transformed γ (%)

80

equilibrium

60
40

M

α

20
0

10 0

10 1

10 2

10 3

Holding time (s)

4

10

γR

80
60
40

M

α

20
0

100

101

102

103

Holding time (s)104Fig. 2 Ferrite transformation kinetics curves of Fe-0.3N alloy
isothermally treated at (a) 750 oC and (b) 600 oC [4].

the amount of retained γ increased with an increased
holding time. A value of 9% retained γ was obtained
at 600 s holding, and remained constant during
further holding.
References[1] Y. Imai, Tetsu-to-Hagané, 51, 2336 (1965).
[2] L. Chen and E. J. Mittemeijer, Scripta Metall. Mater., 24, 509(1990).
[3] T. Tsuchiyama, K. Inoue, K. Hyodo, D. Akama, N. Nakada, S.
Takaki, and T. Koyano, ISIJ Inter., 59, 161 (2019).
[4] M. Sato, T. Murata, S. Shimaya, G. Miyamoto, and T. Furuhara,
ISIJ Inter., 61, 343 (2021)

Mitsutaka Sato (Microstructure Design of Structural Metallic Materials Research Laboratory)
E-mail: mitsutaka.sato.a3@tohoku.ac.jp
URL: http://www.st-mat.imr.tohoku.ac.jp/en/index.html

8

γ(M)

AF

Transformed γ (%)

Nitrogen is an interstitial element andthermodynamically stabilizes the γ phase in Fe
alloys. It is known that the behavior of nitrogen iniron shows a similar tendency to carbon with respect
to the concentration dependence of the change in
the Ae3 or Ms temperature and the lattice constant[1-3]. On the other hand, due to the difference inthermodynamic stability between iron nitride andiron carbide in γ, the eutectoid temperature andconcentration are different between Fe-C and Fe-N
binary systems, and the Ae1 point in Fe-N is lower intemperature and higher in concentration than Fe-C
alloy. These characteristics of Fe-N alloy can beapplied to a new kind of TRIP steel using retained γ
stabilized by N enrichment.
In this study, Fe-0.3mass%N austenite wasprepared by a gas nitriding process. The nitrided
sample was directly dropped into a salt bath heatedto the α+γ two phase region of 600–750 °C andisothermally treated for 3–3600 s. The microstructureof the heat-treated samples was observed using FESEM, and the volume fraction of constituent phases
was determined by point counting and XRD.
Figure 1 shows OM images of Fe-0.3N alloy
isothermally treated at 600–750 °C for various
period of times. At 750 °C, AF is formed at the γ
grain boundary after 5 s. Transformation rapidly
progresses by 60 s, and the γ grain boundaries arecovered by AF. At 600 °C, AF and WF are formed
along the γ grain boundary, and MartensiteAustenite constituent (MA) exists between adjacent
WFs.
Figure 2 shows the transformation kinetics
curve of the isothermally treated samples. In the 750°C sample, the α volume fraction in the early stage
was small, and reached about 10% after 10 s. The
transformation then proceeded more rapidly and an
equilibrium volume fraction of 65% was obtained at
3600 s. At 600 °C, the α transformation was fasterdue to the increasing driving force, and the initial α
volume fraction was much higher than that of 750°C. From the XRD measurement, it was found that

IMR KINKEN Research Highlights 2022

Growth Sequence of Long-Period Stacking-Ordered Phase in
Mg-Al-Gd Alloy Investigated by Correlative Atom Probe
Tomography and Scanning Transmission Electron Microscopy

Atom probe tomography (APT) and scanning transmission electron microscopy (STEM) were used correlatively

to explore atomic-scale local structure and chemistry of the same area in the vicinity of the growth front of along-period stacking ordered (LPSO) phase in a ternary Mg-Al-Gd alloy. The correlative method revealed thegrowth sequence of the LPSO phase in Mg-Al-Gd alloy.

Mg-M-RE (M: metal, RE: rare-earth elements)alloys such as those in Mg-Zn-Y and Mg-Al-Gd
systems have received considerable attention as a
new class of structural materials. In these Mg-M-RE
alloys, unique platelet precipitates so-called‘synchronized’ long-period stacking ordered (LPSO)
phases are known to form. The synchronized LPSO
phase consists of hexagonally-arranged closepacked atomic layers stacked along their plane
normal ([0001] in the hexagonal closed packed (hcp)
notation), in which M and RE atoms are enriched toform M6RE8 atomic clusters with the L12-type atomic
arrangement based on face-centered cubic stacking
in four consecutive atomic layers that are bounded byseveral Mg layers with hcp stacking.
Scanning transmission electron microscopy(STEM) with angstrom spatial resolution, in particular
Z (atomic number)-contrast imaging by high-angle
annular dark-field (HAADF)-STEM has provided
various structural and chemical information for LPSO
phases at an atomic scale. However, differentiating
atoms with close atomic numbers is usually very
difficult. Differentiating Mg (Z=12) and Al (Z=13) in
Mg-Al-Gd ternary alloys is one typical case. Atomprobe tomography (APT), by which a 3D elemental
map can be reconstructed at (sub-) nanometer spatial
resolution for a needle specimen, is a unique methodthat possesses high analytical sensitivity and highmass-resolving capability [1,2]. This means that APT
can provide elemental information that is difficult toobtain simply by atomic-resolution Z-contrast STEM
imaging. However, the spatial resolution in APT
analysis is insufficient to capture crystallographic
information on crystal and defect structures that canbe obtained by TEM/STEM imaging.
In this study, we investigated variations of atomic
structures and elemental distributions on an atomic
scale occurring at the interface region between the
LPSO and Mg phases in a Mg-Al-Gd alloy, using
correlative APT and TEM/STEM in the same regions,in order to better understand how chemical modulationsynchronizes with structural modulation in the growth(a)[0001]

(b)

Al

(c)

Gd

10 nm

-

[1120]

Fig.1 (a) HAADF-STEM image taken along the [1100]
direction. (b), (c) APT maps for Al and Gd in the same
region as the HAADF-STEM image.

sequence of the synchronized LPSO phase.
Figure 1(a), 1(b), and 1(C) respectively show a
HAADF-STEM image taken along the [1100] direction,
and APT maps for Al and Gd in the vicinity of theinterface between the LPSO and Mg phases. (0001)
Gd-enriched atomic layers in the transition region at
the interface changed in the HAADF-STEM contrast
from a row of double-dagger patterns (right-handside) to a slightly brighter line (left-hand side) (Fig.
1(a)). In these (0001) Gd-enriched atomic layers in thetransition region, while Gd enrichment extends acrossthe areas where the HAADF-STEM contrast changes,
Al enrichment is limited only to the layers where a rowof double-dagger patterns is observed. This confirmsthat the formation of Al6Gd8 clusters occurs only aftersufficient Al atoms to form Al6Gd8 clusters reach therelevant portions [3].
References[1] T. Yoshiie, K. Inoue, K. Yoshida, T. Toyama, Y. Satoh, and Y.
Nagai, Philos. Mag. 101, 1202 (2021).
[2] D. Egusa, K. Inoue, Y. Nagai, and E. Abe, Mater. Charact. 177,
111153 (2021).
[3] K. Inoue, K. Yoshida, Y. Nagai, K. Kishida, and H. Inui, Sci. Rep.
11, 3073 (2021).

Yasuyoshi Nagai, Koji Inoue, and Yusuke Shimada (Irradiation Effects in Nuclear and Their Related Materials Research Laboratory)
E-mail: koji.inoue.e2@tohoku.ac.jp
URL: http://www.imr.tohoku.ac.jp/en/about/divisions-and-centers/research-division/11.html

IMR KINKEN Research Highlights 2022

9

Infrastructural Materials

Microstructure Creation via High-pressure Hydrogenation and
Subsequent Dehydrogenation in a Face-Centered Cubic SteelH

ydrogen in steels has the potential to improve mechanical properties via alteration of phase stability and plasticity.
A stoichiometric composition of hydrogen can be introduced for steel compositions, enabling unconventional
diffusionless transformation. For instance, hydrogenation/dehydrogenation treatment in an fcc steel resulted in afine lath bcc structure arising from diffusionless transformation with the sequence of face-centered cubic(fcc)→hexagonal close-packed (hcp)→double hexagonal close-packed (dhcp)→body-centered cubic(bcc).
The use of diffusionless transformation has been
key to designing high-strength steel and iron alloys.
The strength of the diffusionless transformation phasecan be increased by increasing the content of interstitialatoms such as carbon and nitrogen, microstructure
boundary density, and dislocation density. Therefore,
one strategy for improving the strength of steel alloy is
to use the interstitial elements to control the substructureof the diffusionless transformation phase. Hydrogen isalso an interstitial element in steels, and it has recently
been noted as a promising element that enables thecontrol of microstructures associated with diffusionlesstransformation [1]. Moreover, a large amount ofhydrogen can be introduced into steel by pressurizing
the sample with hydrogen, causing a dramatic change
in microstructure [2]. Here, we examine the effect ofhydrogen on the microstructure associated withdiffusionless transformation in steels.
In this study, we used a SUS304L metastable
austenitic stainless steel. Two SUS304L samples werepressurized to 9 GPa without and with a hydrogensource (AlH3), heated to 973 K, and subsequently
depressurized at 293 K. Some interesting differenceswere found between the samples with and withouthydrogenation. First, the constituent phases weredifferent; the microstructure without hydrogen mainly
consisted of fcc phase, whereas the hydrogenatedmicrostructure was fully composed of bcc phase after
depressurization. In terms of microstructure
morphology, the non-hydrogenated sample showedequi-axed coarse grains with some thin plates (Fig.
1(a)). In contrast, the hydrogenated microstructure
morphology was a fine lath (Fig. 1(b)), which is a typicalmorphology of bcc diffusionless transformation phasein steels. In addition, the dislocation density was higher
in the hydrogenated sample than that in the nonhydrogenated sample. As the dislocations that wereintroduced during the pressurization were removed
during recrystallization at 973 K, the numerous
dislocations observed were introduced during thecooling and depressurization. Furthermore, through insitu diffraction experiments, the transformation

Fig. 1 Inverse pole figure maps showing the microstructures
after high-pressure heat treatment (a) without and (b)with hydrogen [3].

sequence in the hydrogenated sample was clarified tobe fcc→hcp→dhcp→bcc.
The important finding here is the fact that “thehydrogenation–dehydrogenation treatment could
refine the microstructure (below 300 nm) and introduce
numerous dislocations by inducing/promoting
diffusionless transformation”. It is also noteworthy that
SUS304L does not show a microstructure that consists
fully of the bcc phase arising from diffusionlesstransformation, as long as the steel is not severely
deformed. That is, we can say that the hydrogenation–
dehydrogenation
treatmentcancreateanunconventional microstructure in the metastable fcc
steel. The fine microstructure with numerous
dislocations was found to show higher hardness thanthat of the non-hydrogenated sample. Thus, ahydrogenation–dehydrogenation treatment could be
used for developing high-strength steels in the future.
References[1] M. Koyama, C. Hao, E. Akiyama, and K. Tsuzaki, Metall. Mater.
Trans. A 51, 4439 (2020).
[2] M. Koyama, H. Saitoh, T. Sato, S. Orimo, and E. Akiyama, Mater.
Lett. X 11, 100078 (2021).
[3] M. Koyama, H. Saitoh, T. Sato, S. Orimo, and E. Akiyama, Sci.
Rep. 11, 19384 (2021).

Motomichi Koyama (Environmentally Robust Materials Research Laboratory)
E-mail: motomichi.koyama.c5@tohoku.ac.jp
URL: https://akiyamaimr-e.amebaownd.com/

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IMR KINKEN Research Highlights 2022

IMR KINKEN Research Highlights 2022

Co-Cr-Mo Crystal Fibers Fabricated from the Melt by
Unidirectional SolidificationAnovel fabrication technique for CCM alloy crystal fibers was developed by unidirectional solidification directlyfrom the melt using the alloy-micro-pulling-down (A-µ-PD) method. Compared with conventional methods, theproposed innovative technique is characterized by low cost, time saving, and low loading. The growth rate in the
A-µ-PD method had a noticeable effect on the fabrication of single- or poly-crystalline CCM fibers.
The micro-pulling-down (µ-PD) method is appropriate
for growing shape-controlled single crystals directly fromthe melt. Based on the shape-control technique of theµ-PD method, we previously developed an alloy-µ-PD(A-µ-PD) method for the fabrication of metal and alloyfibers directly from the melt [1].
Co-Cr-Mo (CCM) alloys have been investigated forvarious applications of biomedical materials. However,
the mechanical properties of as-cast CCM alloys arelimited; in particular, the low ductility and fatigue strength
are a matter of concern for applications.
In this study, we developed an innovative techniqueto fabricate CCM crystal fibers from the melt using the
A-µ-PD method without the problem of the poor workabilityof CCM alloys [2].
CCM fibers were fabricated by the A-µ-PD method
using an Al2O3 crucible. The liquid-solid interface was
located just below the crucible bottom, and the fabricated
CCM fiber diameter could be controlled by maintaining
the position of the liquid-solid interface within the crucible
hole during the fiber fabrication.
The SEM image of φ2 mm CCM fiber grown at 0.5mm/min (CCM2[0.5]) was clearly different from those offibers grown at 0.1 and 0.3 mm/min (CCM2[0.1] andCCM2[0.3]) (Fig.1a). The results confirmed that CCM2[0.5]fiber was composed of two phases, whereas CCM2[0.1]and CCM2[0.3] fibers were composed of a single phase.
According to these phase maps, CCM2[0.1] andCCM2[0.3] fibers were composed of only the hcp-εphase. In contrast, both the fcc-γ-phase and hcp-ε-phasewere observed in CCM2[0.5] fiber. The results of SEM and
EBSD observations confirmed that the martensitic
transformation from the fcc-γ-phase to the hcp-ε-phaseproceeded to completion during the fabrication of
CCM2[0.1] and CCM2[0.3] fibers. The appearance of fccγ-phase in CCM2[0.5] fiber implied that parts of the fccγ-phase remained without martensitic transformation
during and after the fiber fabrication, owing to the relatively
fast growth rate. In addition, according to the growth ratedependence of the fcc-γ-phase ratio, the fcc-γ-phaseappeared at growth rates greater than 0.5 mm/min; it
increased considerably when the growth rate increased in
the range of 0.5–5 mm/min and increased slightly whenFig.1 (a) SEM images and phase maps of CCM2 fibers,and (b) stress-strain curves of CCM2 specimens withthe photographs of specimens after tensile test.

the growth rate increased in the range of 5–10 mm/min.
In the stress–strain curve of CCM2[0.5], the tensile
deformation behavior was comparable to that of the CCM
specimen prepared by casting (Fig. 1b). In contrast, theelongation of CCM2[0.3] was significantly higher than thatof CCM2[0.5]. The elongation values of CCM2[0.3] andCCM2[0.5] were approximately 120% and 8%,
respectively.
References[1] Y. Yokota, T. Nihei, K. Tanaka, K. Sakairi, V. Chani, Y. Ohashi, S.
Kurosawa, K. Kamada, and A. Yoshikawa, Adv. Eng. Mater. 20,
1700506 (2018).
[2] Y. Yokota, T. Nihei, S. Abe, and A. Yoshikawa, Adv. Eng. Mater. 23,
2100144 (2021).

Yuui Yokota and Akira Yoshikawa (Advanced Crystal Engineering Research Laboratory)
E-mail: yui.yokota.a5@tohoku.ac.jp, akira.yoshikawa.d8@tohoku.ac.jp
URL: http://yoshikawa-lab.imr.tohoku.ac.jp/index-e.html

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Infrastructural Materials

Decoupling Between Calorimetric and Dynamical Glass
Transitions in High-Entropy Metallic Glasses

Glass transition is one of the unresolved critical issues in solid-state physics and materials science. Here, we

explored the correlations between the calorimetric and dynamical glass transitions of three prototypical highentropy metallic glass systems, which present a depressed dynamical glass transition phenomenon, owing tosluggish diffusion, decreased dynamic, and spatial heterogeneities from high mixing entropy.

Metallic glasses (MGs) exhibit uniquethermodynamic and dynamic characteristics,
especially when approaching the glass transition
temperature (Tg). The conventional MG design strategy
is based on a principal element with adding of
secondary elements around the eutectic points of thephase diagrams. This restricts the discovery of MGs
with divergent physical and mechanical properties.
Recently, an intriguing alloy design approach was
proposed [1], defined as multiple-principal-element
alloys or high entropy alloys (HEAs), which exhibits
great potential for developing advanced structural andfunctional materials. However, the core criticalbehaviors of HEAs, especially the effect of sluggish
diffusion on the thermodynamic and dynamic
properties of high entropy metallic glasses (HEMGs)
have not been studied.
We utilized the strategy of equivalent substitution
elements to design La(Ce)-based, Pd(Pt)-based andTi(Zr)-based MGs and HEMGs, as model systems toinvestigate the high entropy effect on the structure anddynamics of glass-forming alloys [2]. The mixing
entropy was 1.38R, 1.67R, and 1.57R (Fig. 1a) for thedesigned LaCe-, PdPt-, and TiZr- HEMGs, which ishigher than the value generally defined as high entropy(1.36R). Differential scanning calorimeter (DSC) traces

obtained at a heating rate of 20 K/min are shown in
Fig. 1b. The obvious glass transition and crystallization
signals confirm the glassy state of the three samples.
Calorimetric Tg is determined from the intersection of
the tangent lines of the onset of transformation and isindicated by arrows (Fig. 1b). Figure 1c presents thetemperature dependence of the loss modulus of the
HEMG at 1 Hz with a constant heating rate of 3 K/min(normalized by the maximum peak value). Tworelaxation modes are seen, termed the β - andα-relaxation, from low to high temperatures,
respectively. Our findings indicate a decoupling
between the calorimetric and dynamical glasstransitions of HEMGs.
Based on the present study, the effect of highmixing entropy on the glass transition and crystallization
behaviors of the representative HEMGs was proposed.
It is expected that these HEA ‘core effects’ will benefit
studies on fundamental issues, such as the glasstransition, relaxations, and aging behaviors of MGs.
References[1] J.-W. Yeh, S.-K. Chen, S.-J. Lin, J.-Y. Gan, T.-S. Chin, T.-T. Shun,
C.-H. Tsau, and S.-Y. Chang, Adv. Eng. Mater. 6(5), 299 (2004).
[2] J. Jiang, Z. Lu, J. Shen, T. Wada, H. Kato, and M. Chen, Nat.
Commun. 12, 3843 (2021).

Fig. 1 The mixing of entropy, calorimetric and dynamical behaviors. (a) Calculated mixing entropies for the three MGs systems. (b)DSC traces (heating rate of 20 K/min) of the La(Ce)NiAl system, the arrows indicate the calorimetric Tg. (c) Temperature dependenceof the loss modulus of the LaCe MGs system at 1 Hz with a constant heating rate of 3 K/min, normalized by the maximum peakvalue. The arrows indicate the α-relaxation temperature (Tα), and the inset shows the evolution of Tg and Tα with the components.

Hidemi Kato (Non-Equilibrium Materials Research Laboratory)
E-mail: hikato@tohoku.ac.jp
URL: http://www.nem2.imr.tohoku.ac.jp/index-e.html

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IMR KINKEN Research Highlights 2022

Mechanism of Grain Boundary Cracking in Non-Weldable
Superalloy Alloy713ELC Fabricated with Powder Bed
Fusion Additive Manufacturing Using an Electron BeamGrain boundary cracking is a major problem limiting the fabrication of non-weldable superalloy with powder
bed fusion additive manufacturing using an electron beam (PBF-EB). This study has revealed the cracking
mechanisms and demonstrated a process-parameter-dependent cracking criterion for guiding the process
design of PBF-EB to achieve crack-free samples of Alloy713ELC.

Although the grain refinement was considered to be
The γ’-(Ni,Ti)3Al precipitation-strengthened Nieffective for inhibiting GB cracking, this study
base superalloys, e.g. Alloy713ELC, are capable ofindicates experimentally that fine-grained samples
serving at temperatures near their melting points
can be cracked, while coarse-grained samples canand have been widely used in the hot sections ofbe crack-free. The cracking propensity in thegas turbine engines. However, this class of
optimized samples can be ranked by using a quasisuperalloy with a high volume fraction of γ’
total plastic strain index (QTPSI), which is defined
precipitates is classified as non-weldable superalloy,
and calculated via thermo-mechanical analysis.
and usually exhibits a large grain boundary (GB)The total plastic strain level is a critical cracking
cracking propensity in additive manufacturing. Thisfactor, and a larger scan speed tends to elevate thehas severely limited the application of powder bed
total plastic strain level, exhibiting a larger deviation
fusion additive manufacturing using an electron
beyond the QTPSI. In addition, through comparing
beam (PBF-EB), which is one kind of 3D printing
Alloy713ELC with the weldable superalloy Alloy718
technology enabling near-net shaping of metallic
via thermo-mechanical analysis based on thecomponents with complex shapes, in processing
mechanical property values measured at elevatedthe non-weldable superalloys.
temperatures, it was found that the non-weldability
Although processing non-weldable superalloys
in Alloy713ELC can be attributed to its thermal
with PBF-EB has been extensively studied in recent
expansion effect. This thermal expansion effect,
years, the mechanism of GB cracking is still unclear.
combined with the liquation effect and the strainGB cracking in non-weldable superalloy fabricatedage cracking effect, reveals the intrinsic cause ofwith PBF-EB is affected by the interaction of multiple
non-weldability in Alloy713ELC.
factors including mechanical and compositional
effects. Despite the liquation mechanism having
References
been studied in-depth, there is not an in-depth[1] Y. Lei, K. Aoyagi, K. Aota, K. Kuwabara, and A. Chiba, Acta
understanding of the mechanical effect that triggers
Mater. 208, 116695 (2021).
GB cracking, due to the complexity of the highdimensional process parameter
space and scan strategy in the
PBF-EB process. In addition, it isnecessary to correlate the GB
cracking mechanisms with thecriterion of non-weldability basedon the content of (Al+0.8Ti).
This study [1] applied amethod based on machinelearning to optimize the highdimensional PBF-EB parameter
space for Alloy713ELC. Thisapproach enabled fabricating
Fig. 1 (a) Cracked vs crack-free: PBF-EB samples with various QTPSI and scan speed.
and comparing many cracked(b) Non-weldable Alloy713ELC vs weldable Alloy718: Five indexes calculated via
and crack-free PBF-EB samples,thermo-mechanical analysis, reflecting the non-weldability. E and α denote effective
which have various cracking
elastic modulus and thermal expansion coefficient respectively [1].
factors and few process defects.
Kenta Aoyagi (Deformation Processing Research Laboratory)
E-mail: kenta.aoyagi.e7@tohoku.ac.jp
URL: http://www.chibalab.imr.tohoku.ac.jp/english/index.html

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Infrastructural Materials

Mechanism of Enhancement of Cathodoluminescence Intensity
of Free Lime in Steelmaking Slag by Reheating and Quenching

We have recently developed a method to determine free lime content in steelmaking slag from the illuminatedareas related to free lime in a cathodoluminescence (CL) image. To detect the illumination, the slag must be
previously quenched from 1000°C to room temperature. The factors determining the enhancement ofluminescence of free lime were investigated. We found that the enhancement of the CL intensity of the free lime
is attributed to the increase in the oxygen vacancies by the quench.

Iron and steel manufacturing industries haveaggressively tackled the reduction and reuse of
byproducts to comply with current environmental
regulations. The steelmaking process leads to theworldwide production of huge amounts ofsteelmaking slag as byproduct. Steelmaking slag
has been mostly reused in road construction. Free
lime in steelmaking slag causes road fracturingowing to a volumetric expansion upon reacting withthe moisture and carbon dioxide in the air [1]. Thus,
determining the free lime content in steelmaking
slag is crucial for its safe reuse in road construction.
To meet the demand for a simple method todetermine the free lime content, a method has been
recently developed to rapidly derive this value by
CL imaging of steelmaking slag, previously
quenched from 1000°C to room temperature,according to the illuminated areas corresponding tofree lime (luminescence peak at 600 nm) [2]. Thisquenching is required to obtain intense CL from freelime, but the mechanism of such signal enhancement
is still unknown. Therefore, the present study
investigated the mechanism by comparing the
microstructures, CL images, and CL spectra of freelime in quenched and unquenched steelmakingslag.
A significant number of dislocations weredetected in the quenched slag sample, which could
be responsible for the intense luminescence at 600
nm (2.07 eV), whereas the unquenched sample,
which showed no clear luminescence at 600 nm(2.07 eV), exhibited much fewer dislocations (Fig. 1).
The results of this study [3] and previous reports on
the luminescence of CaO suggest that theluminescence related to the free lime, which
originated from Mn2+ ions substituting Ca2+ ones, isprobably excited by the luminescence from oxygen
vacancies (F+ center) in the free lime (Fig. 2).
Therefore, the increase in oxygen vacancies
enhances the intensity of this CL peak after
quenching.

Fig. 1 Scanning transmission electron (bright field) micrographsof the cross-sections of free lime from (a) a slag sample
quenched from 1000 °C and (b) an as-received one. Someof the dislocations are indicated by the arrows.

Fig. 2 Schematic diagram of the radiative transition related
to luminescence from the F+ centers and Mn2+ ions infree lime.

References[1] S. Chatterji, Cem. Concr. Res., 25, 51 (1995).
[2] S. Imashuku and K. Wagatsuma, Metall. Mater. Trans. B, 51B,
2003 (2020).
[3] S. Imashuku, M. Nagasako, and K. Wagatsuma, Microsc.
Microanal., 27, 484 (2021).

Susumu Imashuku (Analytical Science Research Laboratory)
E-mail: susumu.imashuku.e8@tohoku.ac.jp
URL: http://wagatsuma.imr.tohoku.ac.jp/

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IMR KINKEN Research Highlights 2022

Visible-Light–Induced Photocatalytic Activity of Nitrogen-doped TiO2

T

itanium and its alloys are frequently used as biomaterials because of their good biocompatibility and highcorrosion resistance. In this study, N-doped TiO2 was formed on a Ti substrate, and the antibacterial activity
and reactive oxygen species resulting from the visible-light–induced photocatalytic activity of the N-doped
TiO2 were investigated.
Titanium dioxide (TiO2) forms on surfaces oftitanium (Ti) implants and plays an important role in theosseointegration between Ti and bone. Numerous
studies have reported that anatase-type TiO2 exhibitshigh photocatalytic activity; when it is irradiated withultraviolet light, it reacts with water or O2 surrounding it
and generates reactive oxygen species (ROS). In
addition, hydrogen peroxide (H2O2) and hydroxyl
radicals are known to be generated as ROS on TiO2
photocatalysts. N-doped TiO2 also exhibits visiblelight–induced photocatalytic activity. N-doped TiO2
subjected to NaOH and hot water and heated in anammonia (NH3) gas atmosphere showed visible-light–
induced antimicrobial activity and biocalcification
ability [1], [2]. We have previously investigated Cudoped TiO2 prepared by the alkaline and heat treatmentof Ti metal [3].
The objective of this study is to investigate theantibacterial activity and the ROS generated via visiblelight–induced photocatalytic activity on N-doped TiO2.
To prepare N-doped TiO2, we polishedcommercial-grade pure Ti (cp Ti) plates and soaked
them in NaOH solution and hot water. These plates
were subsequently heated at 600°C for 3 h under an
NH3 gas atmosphere in a tubular electric furnace.
Measurements confirmed the formation of hydroxyl
radicals. Electron-spin resonance (ESR) spectroscopy
was performed to quantify the ROS.
Figure 1 shows the measurement results ofhydroxyl radicals generated by the visible-light
photocatalysis of cp Ti or N-doped TiO2 (600°C, 3 h).
The results show that more hydroxyl radicals weregenerated with a N-doped TiO2 plate than with a cp Ti
plate.
Figure 2 presents the antibacterial effect toward
Escherichia coli (E. coli) of the samples of cp Ti andN-doped TiO2 plates (600°C, 3 h) subjected to visiblelight irradiation. The count of viable E. coli was much
lower after the treatment with a N-doped TiO2 plate
than after the treatment with a cp Ti plate. A significant
difference between them was inferred.
N-doped TiO2 prepared in this study exhibited
photocatalytic activity under visible-light irradiation,

Fig. 1 ESR spectra under visible-light irradiation of (a) a pureTi plate (cp Ti) and (b) a N-doped Ti plate (600°C, 3 h).

Fig. 2 Viable count of E. coli on cp Ti and N-doped TiO2
plates (600°C, 3 h) under visible-light irradiation (mean± standard deviation; n = 3).

and hydroxyl radicals were generated. The results
suggested that ROS (especially hydroxyl radicals)
generated by the photocatalytic reaction contributed
to the antibacterial effects toward E. coli.
References[1] M. Kawashita, N. Endo, T. Watanabe, T. Miyazaki, M. Furuya, K.
Yokota, Y. Abiko, H. Kanetaka, and N. Takahashi, Colloids andSurfaces, B: Biointerfaces 145, 285 (2016).
[2] M. Iwatsu, H. Kanetaka, T. Mokudai, T. Ogawa, M. Kawashita, and
K. Sasaki, J. Biomed. Mater. Res. B: Applied Biomaterials 108(2),451 (2020).
[3] K. Suzuki, T. Yokoi, M. Iwatsu, M. Furuya, K. Yokota, T. Mokudai,
H. Kanetaka, and M. Kawashita, J. Asian Ceram. Soc., 9(4) 1448
(2021).

Takayuki Mokudai (Design & Engineering by Joint Inverse Innovation for Materials Architecture)E-mail: tmokudai@tohoku.ac.jp
Hidemi Kato (Project Leader of Design & Engineering by Joint Inverse Innovation for Materials Architecture)E-mail: hidemi.kato.b7@tohoku.ac.jp
URL: http://www.imr.tohoku.ac.jp/en/about/divisions-and-centers/research-division/29.html

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Infrastructural Materials

Development of the Integrated Program for Special Educationin Computational Materials Science and Human Skills Training
Before/With/After COVID-19

Professional development Consortium for Computational Materials Scientists (PCoMS) supports young researchersin computational materials science (CMS) by attempting to broaden their view and extensive knowledge ofinterdisciplinary areas such as materials science (MS), condensed matter physics, molecular science, and materials
design. Introduced bellow is a recent activity by key members of PCoMS. Prof. Terada and coauthors are developing
an integrated program for special education in CMS and human skills and are analyzing its effectiveness.
We aim to develop the PCoMS Innovative
Professional Development program and support graduate
students and young researchers in materials science(MS) to help overcome the gaps between fundamental
research, applied research, and practical applications.
An onsite PCoMS 3-day seminar before COVID-19
was one of the unique subjects in our program where
three objectives could be achieved at once: obtain abroad knowledge of CMS; learn high-performancecomputing techniques, and human skills and transferable
skills (HS) needed for researchers in both industry andacademia [1]. In this seminar, we integrated “scientificlectures” with “HS trainings and group discussion”. The
discussion about the research proposal was conductedin groups of several participants with different
backgrounds, affiliations, and positions. It was required
for research proposals to be related to the topics covered
during the seminar and the research of each individual
participant, which enabled the participants to haveprofessional scientific discussions with other participantsin different fields. On the final day, each group presented
its proposal. Depending on the progress of a group
discussion, we provided training on necessary humanskills, such as tips for team building, methods ofbrainstorming, presentation tips, etc. The satisfaction of
the participants for the lectures is typically low when the
difficulty level of the lectures is not appropriate. However,based on surveys, we found that most participants weresatisfied with group discussions, even though they think
it is a difficult task. We also found that some participants
believed that they did not need HS training before
attending the seminar. However, after completing HS
training and group discussion, they recognized theimportance of improving HS. This result suggests that the
integrated education program is effective in motivating
participants to broaden their scientific knowledge of MS
and improve their HS. Implementing such an integrated
program requires the program coordinator and thefacilitator of the group discussion who have CMS
expertise and human skill training knowledge. The limited
implementation of such seminars is a different issue.
Another finding is the importance of encouraging theparticipants to be active and participate in the discussion.
The lecturers felt that they could convey the content
sufficiently during their lecture to receive positive
feedback from the participants only when there was anactive discussion between the participants and thelecturers.
We are now developing the online and/or hybrid
seminar with/after COVID-19 [2]. After 2020, PCoMS held
only online lecture-type seminars. These online seminars
attracted a wider range of participants compared to onsite seminars before COVID-19. In particular, the ratio ofparticipants working in the industry increased. Based ona participants’ survey, we found that the satisfactionlevels remained almost unchanged, regardless of theseminar format (online lecture-type seminars vs. on-site/
hybrid lecture-type seminars). These results suggest thatonline lecture-style seminars are effective. However,there were some problems; for example, the participants
had some difficulties asking questions. Furthermore, thelecturers could not gauge the level of understanding of
the participants in some cases. We will need to overcome
these problems and develop the materials and contents
suitable for the online group discussion and HS training.
References[1] Y. Terada, “Development of the short-term integrated program forengineering education and human skills training -Case study ofProfessional development Consortium for Computational Materials
Scientists”, The 69th Japanese Society for Engineering Education
Annual Conference, Sep 9, 2021.
[2] Y. Terada, T. Kawakatsu, M. Kubo, T. Takagi, and I.-C. Chen,“Support for young researchers in computational materials science
under COVID-19 -case report: seminar activities of PCoMS”, JIM Fall
Meeting 2021, Sep 17, 2021.

Yayoi Terada (Professional development Consortium for Computational Materials Scientists)
E-mail: yayoi.terada.b8@tohoku.ac.jp
Momoji Kubo (Project Leader of Professional development Consortium for Computational Materials Scientists)
E-mail: momoji@tohoku.ac.jp
URL: http://pcoms.imr.tohoku.ac.jp/index_e.html

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Energy-Related Materials

IMR KINKEN Research Highlights 2022

Research

Energy-Related Materials

Molecular Dynamics Simulation for High Functional Materials
Design and High-Performance System

Recent materials design for high-functional materials and high-performance systems requires a deep understandingof multiphysics phenomena including chemical reaction, friction, impact, fluid, and heat. We applied our developed
multiphysics computational simulator based on the molecular dynamics method and found the multiphysics phenomena
contributing to materials design for mechanical engineering applications such as power plants and electronics.

High-functioning and high-performance materials
are necessary for a wide variety of fields including
power plants, electronics, and tribology, to addressing
energy and environmental problems and fordevelopment of high-performance systems. A detailed
understanding of multiphysics phenomena including
chemical reactions, friction, impact, fluid, and heat, arerequired for design of the materials. However, traditional
simulation methods such as first-principles calculations
and fluid mechanics cannot simulate the above
multiphysics phenomena. We therefore developed amultiphysics simulator using methods including
reactive molecular dynamics, and tight-binding
quantum chemical molecular dynamics (TB-QCMD),
for developing next-generation materials designs [1-3].
In next-generation power plants, supercriticalwater (i.e., water with a temperature above 374 °C anda pressure above 22 MPa) is used to increase theenergy conversion efficiency. However, supercriticalwater degrades body centered cubic (BCC) ironbased alloys, leading to potential dangers. To reveal
the effect of supercritical water on the fracture of ironbased alloy materials, we performed a tensile simulationof BCC iron in a supercritical water environment using
the reactive molecular dynamics method [1]. The
results show that tensile strain along the [110] directionof BCC iron may exhibit a much higher tensile strengthand lower sensitivity to the environment compared withother directions. This is because yielding of iron along
the [110] direction originates from the homogenous
generation of hexagonal close packed (HCP)
precursors inside the bulk iron rather than at thesurface (Fig. 1), which limits the effects of surface
chemical reactions with supercritical water on theyielding behavior.
To elucidate the chemical mechanical polishing(CMP) mechanism of diamond, we performed CMP
simulation of a diamond surface with OH radicals using
the tight-binding quantum molecular dynamics method[2]. We clarified that the diamond CMP mechanism
consists of the coupled phenomena of (i) generationand desorption of gas molecules such as CO2 andH2CO3 (Fig. 2b,c), and (ii) generation and removal of(b) strain=10.88%(a)
BCC
FCC Cross-sectional view
HCP
othersIMR KINKEN Research Highlights 2022

stacking fault(110) plane

Fig. 1 Cross-sectional view of a BCC iron bulk in the
supercritical water environment at strains of (a) and (b)10.88% and (c) 10.98%.
load

(a)

O

(b)
velocitySi
SiO2 abrasive
grainC
diamond(001) H(c)

CO2
desorption

C-O-C bondgeneration(d)Removedgraphitic ring

Generated graphitic ring

Fig. 2 Snapshots of the CMP process of the diamond(001) surface with a SiO2 abrasive grain and OH radicals
at (a) 0.0, (b) 16.4, (c) 317.0, and (d) 355.8 ps. The watermolecules and OH radicals are not displayed for clarity.

graphitic rings (Fig. 2c,d). Based on these results, we
proposed that the graphitization of the diamondsurface induced by oxidation is important to improve
efficiency of the diamond CMP.
References[1] Q. Chen, J. Zhang, Z. Liu, Y. Wang, Y. Ootani, J. Xu, N. Ozawa,and M. Kubo, Scr. Mater. 202, 113997 (2021).
[2] K. Kawaguchi, Y. Wang, J. Xu, Y. Ootani, Y. Higuchi, N. Ozawa,and M. Kubo, ACS Appl. Mater. Interfaces 13, 41231 (2021).
[3] Y. Wang, K. Hayashi, Y. Ootani, S. Bai, T. Shimazaki, Y. Higuchi,
N. Ozawa, K. Adachi, M.-I. De Barros Bouchet, J.M. Martin, and M.
Kubo, Langmuir 37, 6292 (2021).

Momoji Kubo (Materials Design by Computer Simulation Research Laboratory)
E-mail: momoji@tohoku.ac.jp
URL: http://www.simulation.imr.tohoku.ac.jp/eng/index.html

18(c) strain=10.98%

IMR KINKEN Research Highlights 2022

Radiation Tolerance of ODS Alloys for Advanced Nuclear Systems

Oxide dispersion strengthened (ODS) alloys are used in advanced nuclear fission and fusion reactor systems
because of their excellent radiation tolerance through the fine dispersion of nano-scale oxide particles. We
found that the coarsening and/or segregation at grain boundary of Y-Zr oxide particles in the alumina scale of
ODS ferritic alloy occurred after Fe-ion irradiation. Our ultra-small testing technologies have an advantage inevaluating the interfacial bonding strength of thin-coating/substrate systems, even after irradiation experiments.
Materials resistant to extreme environments,
such as oxide dispersion strengthened (ODS) alloys[1,2] and ceramics [3], are crucial for realizing
advanced nuclear systems.
In particular, Al-added ODS ferritic alloys havebeen developed as an accident-tolerant fuel cladding
for commercial light water reactors, Generation IV
systems, and as blanket structural materials of fusion
reactors, because of their excellent high-temperatureoxidation resistance through the formation of stable
alumina scale. While ODS alloys are known to havesuperior radiation resistance against void-swellingand irradiation hardening, there have been no studies
on the effect of radiation on the alumina scale formedon the Al-added ODS ferritic alloys. In this study [1],Fe-ion-irradiation experiments were performed on
pre-oxidized Al-added ODS ferritic alloy. The depth
profile of nanoindentation hardness in Fig.1(a)showed that irradiation softening occurred in thealumina layer. Transmission electron microscopy
indicated that the Y-Zr oxide particles inside thealumina scale were coarsened and/or segregatedalong grain boundaries by the ion irradiation, as
shown in Fig.1(b,c). This is believed to be derived
fromtheirradiation-induced
dissolutionreprecipitation of the Y-Zr oxide particles. Further
studies are needed to clarify the stability andcorrosion resistance of the alumina scale in Al-added
ODS ferritic alloys under irradiation in a corrosive
environment. For example, the interfacial bonding
strength between alumina scale and ferritic matrix is
an important factor for judging the availability in harshenvironments.
To directly evaluate the interfacial bonding
strength of such a thin coating on the substratematerials, a micro-double notch shear compression
test was developed and carried out on tungstencoated ferritic steels that can be used for the innerwalls of fusion reactors, as shown in Fig.1(d) [4].
Focused ion beam (FIB) and nanoindentation
techniques have enabled ultra-small testing
technologies (USTT) to evaluate the mechanicalproperties of small areas. The micrometer-size
compressive specimens made by FIB were examinedby micro-shear compression tests to obtain loaddisplacement curves. Observations of the bonding
microstructure and fracture surface indicated that theobtained shear strength with 1 μm² specimens intheir shearing plane corresponded to the interface
bonding shear strength between tungsten and ferritic
steel. USTTs will also help to investigate the availabilityof ODS ferritic alloys as a radiation-tolerant anticorrosion material, even after irradiation experiments.
References[1] H. Yu, H. Wang, S. Kondo, Y. Okuno, R. Kasada, N. Oono-Hori,and S. Ukai, Nucl. Mater. Ener. 29, 101102 (2021).
[2] Y. Liu, S. Kondo, H. Yu, K. Yabuuchi, and R. Kasada, Nucl.
Mater. Ener. 26, 100903 (2021).
[3] Y. Jimba, S. Kondo, H. Yu, H. Wang, Y. Okuno, and R. Kasada,Ceram. Inter. 47, 21660 (2021).
[4] X. Wu, S. Kondo, H. Yu, Y. Okuno, M. Ando, H. Kurotaki, S.
Tanaka, K. Hokamoto, R. Ochiai, S. Konishi, and R. Kasada,Mater. Sci. & Eng. A 826, 141995 (2021).

Fig.1 (a) irradiation softening of Al2O3 surface layer in ODS ferritic alloy, its cross-sectional images (b) before and (c) after
ion-irradiation, and (d) micro-double notch shear testing procedure for coating

Ryuta Kasada, Sosuke Kondo, Hao Yu, and Yasuki Okuno (Nuclear Materials Engineering Research Laboratory)
E-mail: ryuta.kasada.e7@tohoku.ac.jp
URL: http://www.imr.tohoku.ac.jp/en/about/divisions-and-centers/research-division/13.html

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Energy-Related Materials

ScAlMgO4 as a Promising Substrate for the Epitaxial Growth of GaN

Herein, high-resolution rocking curve measurement and topography were conducted on ScAlMgO4 substrates.
A narrow rocking curve width of 7.2 arcsec was obtained, and the 3D-configuration of dislocations in theinterior of the crystal structure was analyzed through 3D section topography. Burgers vectors of dominating
dislocations with slip planes of (0001) were found to be parallel to the a-axis.
GaN-based thin films are promising materials forthe production of a variety of energy-saving devices
because the performance of these devices depends on
the quality of GaN films. In this context, the homoepitaxial
growth of GaN and related films on bulk GaN substrates
is essential; however, the commercial availability of thesubstrates is limited due to the difficulties associatedwith growing bulk GaN crystals. Generally, epitaxial
GaN film devices are fabricated on foreign substrates,
such as α-Al2O3 and Si; however, the differences in thelattice mismatch and thermal expansion coefficients
between GaN and these foreign substrates have asignificant effect on the device performance. ScAlMgO4(SAM), developed by the Bell Laboratory, can be used
as a substrate for GaN growth during the fabrication ofblue LEDs. SAM has attracted considerable attention
because of the small lattice mismatch and the small
difference in thermal expansion coefficients between
GaN and SAM. Recently, it was reported that highquality SAM substrates, with a diameter of 2 inch, weregrown by the Czochralski (CZ) method in Japan [1,2].
High-resolution rocking curve measurement inreflection geometry was conducted using a Ge440(4-bounce) incident beam conditioner. A significantly
narrow rocking curve width of 7.2 arcsec was obtained
for the SAM 00018 reflection; this indicates the highquality of SAM wafers grown by the CZ method. Figure
1 shows a transmission XRT image for SAM 2240
reflection together with the rocking curve mapping
profile. The SAM wafer can be ranked into two growthareas of the central area just below the seed crystal andthe diameter-expanding area. The central part of thewafer with a diameter of 15–20 mm was free fromstriation patterns; however, it contained a relatively large
curvature of lattice planes. This is in contrast to thatobserved at the outer striation-containing area. Although
the relatively low spatial resolution of a digital X-ray
camera did not allow us to show the details of isolated
dislocations, the overall image with respect to the crystal
quality and the dislocation distribution and arrays is
discussed. In the central part of the wafer, striation
patterns were not detected. The formation of striation
patterns may be correlated with the thermal gradientenvironment at the onset of crystallization together with

Fig. 1 Correlation of XRT image for SAM 2240 and HR-RC
mapping result.

the non-stoichiometric elements absorbed at the growth
front. Dark-colored regions close to the outer rim of thesample are areas that were damaged due to the grinding
process during wafer fabrication. Dislocations at thestriation-free central area appear to form bundles andthe observed dislocation line is parallel to the [0110]
axis. Further analysis, with respect to the XRT image for
the 0330 reflection, revealed that the Burgers vectors ofthese dislocations are parallel to the [2110] axis. This
fact suggests that the dominant dislocations in the SAM
crystal are edge-type dislocations with b // [2110]
slipping on the (0001) plane.
References[1] K. Inaba, K. Sugiyama, T. Fujii, and T. Fukuda, J. Cryst. Growth 574,
126322 (2021).
[2] T. Fukuda, Y. Shiraishi, T. Nanto, T. Fujii, K. Sugiyama, R. Simura, H.
Iechi and K.Tadatomo, J. Cryst. Growth 574, 126286 (2021).

Kazumasa Sugiyama (Chemical Physics of Non-Crystalline Materials Research Laboratory)
E-mail: kazumasa.sugiyama.e6@tohoku.ac.jp
URL: http://www.imr.tohoku.ac.jp/en/about/divisions-and-centers/research-division/15.html

20

IMR KINKEN Research Highlights 2022

IMR KINKEN Research Highlights 2022

Lattice-Misfit Strain Evolution at the Surface of Pt-Ni
Nanoparticles During Electrochemical Reaction Detectedby Bragg Coherent Diffraction Imaging

Enhancement of the sluggish oxygen reduction reaction (ORR) is required to realize efficient electrochemical

devices such as fuel cells and metal-air batteries. Nanoparticles of platinum and its alloys are used as catalysts
for ORR, in which elastic strain at the surface of the nanoparticles potentially enhances their catalytic activity.
Strain evolution of Pt-Ni alloy nanoparticles during electrochemical operation was quantitatively examinedusing a novel imaging technique, Bragg coherent diffraction imaging (BCDI). The strain induced at the surfaceof the nanoparticles, observed in the present study, successfully explains the composition dependence of thecatalytic activity of the ORR in Pt-Ni alloy.

Compressive surface strain
induced by core-shell structureCohgtterin

t sca

eren

The practical efficiency of fuel cells and metalair batteries is impeded by the sluggish oxygen
reduction reaction (ORR), in which Pt and its alloys
are used as the electrochemical catalysts. In Pt-M
(M: other metal elements) alloys, a nearly pure Pt"shell" is formed by dissolving the alloyed metal (M)from the surface of the nanoparticles during thereaction, eventually covering the surface. The
catalytic activity of these particles is therefore
expected to be similar to that of pure Pt. Interestingly,
however, the catalytic activity of “dealloyed” Pt-M
with a Pt shell shows better catalytic activity, which is
attributed to the strain induced at the surface of thenanoparticles. Thus, it is important to reveal thestrain distribution on the Pt shell in order to exploit
this mechanism to design new alloy catalysts.
However, evaluating the strain on the shell ischallenging because it requires a technique that can
image the strain field of the nanoparticles in situ.
In this study [1], details of the strain of exemplary
Pt-Ni alloy nanoparticles were revealed from 3D
images obtained using a novel synchrotron
technique, Bragg Coherent X-ray Diffraction Imaging(BCDI) [2], which enables the detection of strain
inside a particle using X-ray coherence. Pt-Ni
nanoparticles with compositions of Pt2Ni3 (Ni-rich),
Pt1Ni1 (moderate Ni), and Pt3Ni2 (Ni-poor) wereobserved by BCDI during cyclic voltammetry cycles,in which the less noble metal Ni is known to dissolve
electrochemically from the surface. The evolution oftensile strain inside the particles was observed in all
the compositions, strongly indicating the formationof a Pt shell on the surface to mitigate the overall
internal stress by utilizing the lattice mismatch
between the Pt-Ni core and Pt shell. Thus, a coreshell elastic model was used to evaluate the strain in
the Pt shell based on the parameters obtained from

BCDI
Reconstruction

Pt-Ni corePt-rich shell

Ni dissolution

X-ray
Alloy nanoparticle

Fig. 1 A schematic of Bragg coherent diffraction imaging
and core-shell Pt-Ni alloy nanoparticle (left). Observed
compressive strain in the Pt-shell (right) [1]

the 3D images.
Compressive circumferential strain in the shell
was observed for all compositions. The Pt1Ni1
particles exhibited the largest compressive
circumferential strain of 5%. Since it was reported
that compressive strain facilitates ORR [3], this is inexcellent agreement with the previously reported
composition dependence of the catalytic activity of
nm-sized particles among a wide range ofcompositions.
The present study demonstrated that BCDI
enables quantitative determination of the strain on
alloy nanoparticles during electrochemical reactions,which will eventually lead to rational catalyst designby exploiting the strain-induced enhancement of thecatalytic activity in a wide range of electrocatalysts.
References[1] T. Kawaguchi, V. Komanicky, V. Latyshev, W. Cha, E. R. Maxey,
R. Harder, T. Ichitsubo, and H. You, Nano Lett. 21, 5945 (2021).
[2] I. Robinson and R. Harder, Nat. Mater. 8, 291 (2009).
[3] P. Strasser et al., Nat. Chem. 2, 454 (2010).

Tetsu Ichitsubo, Norihiko L. Okamoto, Hiroshi Tanimura, Tomoya Kawaguchi, and Hongyi Li (Structure-Controlled
Functional Materials Research Laboratory)
E-mail: tichi@tohoku.ac.jp
URL: http://ilab.imr.tohoku.ac.jp

IMR KINKEN Research Highlights 2022

21

Energy-Related Materials

Enhanced Anomalous Nernst Effect in Ni/Pt Epitaxial SuperlatticeT

he anomalous Nernst effect (ANE), where the electric field appears in the cross-product direction of magnetizationand temperature gradient in a magnet, has attracted considerable attention as an environmentally-friendly technology
for energy harvesting. We found an enhancement of ANE in metallic superlattices consisting of Ni and Pt layers, andrevealed that the large transverse thermoelectric conductivity plays a major role in the enhanced ANE.
HeaterV

Samplez

IMR KINKEN Research Highlights 2022

S

x

c

ANE

y
Cu blockt = 3 nm0.4

Bulk Ni

12t (nm)

3

4

1.2
0.8

0.0

0.4
0.0
0.0 0.4 0.8

-1.0
-10

0.8

EANE (µV mm-1 )

-1

1.0

1.2

0.0
0

b

-5

0

∇ T (K mm -1)
5
10

H (kOe)Fig.1 (a) Measurement setup for ANE. (b) H dependenceof EANE divided by ∇T for [Ni (t nm) / Pt (1.0 nm)]superlattice with t = 3.0 nm. Inset: the plot of EANE as afunction of ∇T. (c) t dependence of SANE.

hysteresis of EANE /∇T was observed. SANE wascalculated from the slope of the linear fit to EANE asa function of ∇T. Figure 1c shows the t dependenceof SANE. All the samples exhibited large values of
SANE ≥ 0.9 µV K-1, and the maximum SANE =1.14±0.05 µV K-1 was obtained at t = 2.0 nm. It isnoted that the SANE for the Ni/Pt superlattice is oneorder of magnitude larger than that for bulk Ni [2].
From a detailed investigation, the enhanced ANE is
attributable to the large transverse thermoelectric
conductivity. We successfully demonstrated theenhancement of the ANE owing to the formation of
Ni/Pt superlattices [4].
References[1] K. Uchida, T. Kikkawa, T. Seki, T. Oyake, J. Shiomi, Z. Qiu, K.
Takanashi and E. Saitoh, Phys. Rev. B 92, 094414 (2015).
[2] A. Miura, R. Iguchi, T. Seki, K. Takanashi, and K. Uchida,Phys. Rev. Mater. 4, 034409 (2020).
[3] T. Seki, M. Tsujikawa, K. Ito, K. Uchida, H. Kurebayashi, M.
Shirai, and K. Takanashi, Phys. Rev. Mater. 4, 064413 (2020).
[4] T. Seki, Y. Sakuraba, K. Masuda, A. Miura, M. Tsujikawa, K.
Uchida, T. Kubota, Y. Miura, M. Shirai, and K. Takanashi, Phys.
Rev. B 103, L020402 (2021).

Koki Takanashi and Takeshi Seki (Magnetic Materials Research Laboratory)
E-mail: koki.takanashi.d2@tohoku.ac.jp, takeshi.seki@tohoku.ac.jp
URL: http://magmatelab.imr.tohoku.ac.jp/

22

∇T

H

(µV K -1)aBakelite

EANE / ∇T ( µV K )Spin caloritronics, the research field of theinterconversion between charge current (Jc) andheat current (Jq) mediated by spin current (Js) and/or magnetization (M), has attracted much attention
not only for academic interest but also for practicalapplications. Newly discovered spin caloritronic
phenomena have stimulated renewed interest in thethermoelectric phenomena in ferromagnets. One of
the thermoelectric phenomena in ferromagnets isthe anomalous Nernst effect (ANE), in which Jc
appears in the cross-product direction of M and thetemperature gradient (∇T). Although ANE has been
known for a long time, the microscopic physicalpicture of ANE has not been fully understood. In
addition to the fundamental point of view, thismagneto-thermoelectric effect may be beneficial forthermoelectric conversion applications. The key to
ANE-based thermoelectric conversion is to find amaterial with a large anomalous Nernst coefficient(SANE).
We previously reported the enhancement of
ANE in Fe-based metallic multilayers [1], implyingthat the low dimensionality of the layer and/or the
existence of an interface plays a role in the increasein ANE. This suggests that metallic multilayers or
superlattices with a number of interfaces arepromising for achieving a large ANE.
Here, we focus on the combination offerromagnetic Ni and paramagnetic Pt because Ni
is an interesting material for ANE [2] and Pt is a
representative paramagnet with a large spin-orbit
interaction. Perpendicularly magnetized Ni/Pt (001)epitaxial superlattices were fabricated directly on a
non-conductive SrTiO3 substrate [3], and the Ni
layer thickness dependence of ANE was investigatedfor [Ni (t nm) / Pt (1.0 nm)]×N .
Figure 1a shows the measurement setup for the
ANE. By heating one side of the substrate, ∇T was
induced along the in-plane x direction. An external
magnetic field (H) was applied along the out-ofplane z direction. As a result, the electric field of the
ANE (EANE) was detected along the y-direction.
Figure 1b shows the H dependence of the EANE
divided by ∇T for t = 3.0 nm. A square-shaped

IMR KINKEN Research Highlights 2022

Complex Hydride-Based Electrolyte with Hydrogen Cluster
Anion for Room-Temperature Calcium Rechargeable Battery

Calcium batteries are cost effective and possess high battery performance, making them a suitable substitute for Li-

batteries. Still, many challenges remain before calcium batteries can be realized due to a lack of suitable electrolytes with
reductive/oxidative stability and high ionic conductivity. In this study, we developed a new fluorine-free calcium electrolyte
based on a hydrogen cluster (monocarborane) anion that could potentially realize rechargeable calcium batteries.
(a)

H

C

Ca ion

B

THF
DME
(b)
20
Current (mA)

Current Li-ion batteries with high energy densities
are indispensable in applications such as portableelectronic devices, electric vehicles, and grid-scalestorage. However, they are approaching their limits oftheoretical energy density and cost, and Li is not naturally
plentiful. Ca is the fifth most abundant element in the
Earth’s crust and its metal anode has a low reduction
potential (–2.87 V vs. SHE) and high volumetric capacitiesof 2072 mAh cm –3, giving it a comparable cell voltage
and energy density to that of Li. Ca batteries are therefore
cost effective and possess high battery performance,
making them a suitable substitute for Li-batteries [1].
Still, many challenges remain before Ca batteries
can be realized due to a lack of suitable electrolytes
which possess reductive/oxidative stability and high ionic
conductivity. Moreover, realizing a fluorine-free system isdesirable for practical Ca electrolytes because a fluorinecontaining electrolyte intrinsically induces CaF2 formationon the electrode, which hinders Ca diffusion as well as
the Ca plating and stripping processes.
In this study, we developed a highly stable andefficient fluorine-free Ca electrolyte of Ca[CB11H12]2
based on a hydrogen cluster (monocarborane, complex
hydride) anion (Fig. 1a) for room-temperature Ca batteries[2]. The hydrogen cluster anion is known as a weakly
coordinating anion with high reductive and oxidative
stabilities, indicating that an electrolyte with the anion
could also be highly compatible with Ca batteries [3]. The
Ca[CB11H12]2, which was successfully prepared via
simple cation exchange and heating processes, exhibited
low solubilities in tetrahydrofuran (THF) and
1,2-dimethoxyethane (DME), but high solubility in themixed solvent of DME/THF. The 0.5 M Ca[CB11H12]2
electrolyte showed the most promising electrochemical
performances, viz., a high conductivity, wide potential
window, and reversible Ca plating/stripping behavior withhigh Coulombic efficiency (Fig. 1b). In a feasibility study,
we used the this electrolyte in a Ca battery with a sulfur
cathode exhibiting reversible discharge and charge
abilities, demonstrating that the Ca[CB11H12]2 electrolyte
is compatible with a Ca battery system.
The development of a promising electrolyte
candidate based on complex hydrides compatible with

10

Wide potential window0

Stable stripping/plating

10

Plating

20

Ca

Au

Ca
Stripping

30
1

0

Au

Plating Ca

1
2
3
Potential (V vs. Ca2+/Ca)

4

Fig. 1 (a) Graphical image of the new developed calcium
battery electrolyte Ca[CB11H12]2 in DME/THF, (b) Cyclic
voltammograms of Ca plating/stripping with a threeelectrode setup at room temperature with graphicalimage of Ca plating/stripping (inset).

Ca batteries will create future opportunities for exploringother related complex hydride compounds. In addition,
the absence of fluorine and CaF2 formation in thesematerials will pave the way for achieving high cyclability
in Ca batteries.
References[1] M. E. Arroyo-de Dompablo, A. Ponrouch, P. Johansson, and M. R.
Palacin, Chem. Rev. 120, 6331 (2020).
[2] K. Kisu, S. Kim, T. Shinohara, K. Zhao, A. Zuttel, and S. Orimo, Sci.
Rep. 11, 7563 (2021).
[3] R. Mohtadi and S. Orimo, Nat. Rev. Mater. 2, 16091 (2017).

Kazuaki Kisu and Shin-ichi Orimo (Hydrogen Functional Materials Research Laboratory)
E-mail: kazuaki.kisu.b2@tohoku.ac.jp
URL: http://www.hydrogen.imr.tohoku.ac.jp/en/index.html

IMR KINKEN Research Highlights 2022

23

Electronic Materials

IMR KINKEN Research Highlights 2022

ResearchElectronic Materials

Exotic Pairing States in a Spin-Polarized Quantum-Hall Insulator

Emergent physics appears in hybrid systems composed of differently ordered materials. For Cooper pairs, aheterojunction of a quantum Hall insulator and a conventional superconductor is an unusual environment,
which leads them to have exotic pairing symmetry. Our study revealed possible pairing states induced in themetallic edge of a spin-polarized quantum Hall insulator and showed that these pairing states can be detected
via the Josephson effect.

Fig. 1 The geometry of the Josephson junction (top) anddetection of the triplet Cooper pairing (bottom).

The critical current vanishes when the Cooper
pair momentum 2kF is commensurate with thesample width W.

Log IC

Chemical potential

Topological orders and topological phases area field of current active research in condensed
matter physics. The quantum Hall effect is aprominent example of a phenomenon associatedwith topological materials and is realized in a twodimensional electronic system subject to a strong
magnetic field. The most remarkable behavior of theelectronic states in topological materials appears at
the edge or surface. A quantum Hall system has
metallic edge states, where electrons flow
unidirectionally, while the bulk is an insulator.
The surface or edge states of topologicalmaterials such as topological insulators andquantum spin Hall insulators can be engineered byattaching conventionally ordered materials, e.g.,superconductors and ferromagnets. Unlike theseexamples, it is known that the edge states ofquantum Hall insulators are less affected byattached materials due to the unidirectional flow.
Based on this, our study focuses on the electronic
behavior at the interface between a spin-polarized
quantum Hall insulator and a superconductor fromthe perspective of pairing symmetry.
Superconductivity is categorized by thesymmetry of Cooper pairs. In general, this property
is intrinsic to materials. However, a junction with
non-superconducting materials can transformpairing symmetry depending on the electronic
structure of the materials. We showed that Cooper
pairs induced in a spin-polarized quantum Halledge are (i) spin-triplet, (ii) a combination of evenand odd-frequency components, and (iii) have afinite momentum [1].
These exotic pairing states can be confirmed
via the Josephson effect. The spin-triplet pairing
can be detected by the sensitivity to the interface
magnetization. In addition , the momentum of
Cooper pairs can be detected by the vanishing of
the critical current, which is defined by the maximum
Josephson current. The critical current vanishes
when the Cooper pair momentum 2kF iscommensurate with the length of the interface (= thejunction width).

LengthFig. 2 Detection of the Cooper pair momentum by thevanishing critical current.

References[1] R. Nakai, K. Nomura, and Y. Tanaka, Phys. Rev. B 103, 184509(2021).

Kentaro Nomura and Ryota Nakai (Theory of Solid State Physics Research Laboratory)
E-mail: ryota.nakai.b6@tohoku.ac.jp
URL: http://www.bauer-lab.imr.tohoku.ac.jp/home_en.html

26

IMR KINKEN Research Highlights 2022

IMR KINKEN Research Highlights 2022

Twin Boundary Formation at Grain-boundary Groove During
Directional Solidification of Compound Semiconductor InSb

T

he formation of twin boundaries at the grain-boundary groove of InSb was experimentally observed in situ. It was
shown that the twin boundaries are generated when rapid growth occurs at the grain-boundary groove bounded by
facet planes. By calculating the relationship between the probability of twinning and the degree of undercooling required
for twinning, we proved that the twin nucleation in InSb occurs preferentially at the bottom of the grain-boundary groove.
Formation of twin boundaries is detrimental inboth bulk single-crystal growth and bulk poly-crystal
growth of semiconductors, because the density ofgrain boundaries in the crystal significantly influences
the quality of substrates cut from a bulk crystal.
Recently, in the directional growth of Si, it wasobserved that a faceted groove formed at thejunction of a crystal-melt interface and a grainboundary, and that twin nucleation occurred at thebottom of the grain-boundary groove [1,2]. A
twinning model at the grain-boundary groove has
also been proposed [3]. While the occurrence oftwinning at the grain-boundary groove duringsolidification of Si has been discussed, twinningduring the solidification of compound semiconductors
has been less studied. In this study, to understandthe effect of the grain-boundary groove on twinningduring the solidification of compound semiconductor,
we observed a crystal-melt interface of InSb [4].
Figure 1(a) shows the crystal-melt interface
during directional solidification of InSb. It was clearlyobserved that a groove bounded by facet planes
was formed at the crystal-melt interface due to theexistence of a grain boundary. The depth of thegroove increased with time. When the depth of thegroove reached approximately 100µm, the groove
was filled by the rapid growth. This shows that thedegree of undercooling in the groove was large
locally. We confirmed that twin boundaries wereformed during this process, as schematically shownin Fig. 1(b). We calculated the probability of twin
nucleation Ptwin at the grain-boundary groove as afunction of undercooling ΔT. We assumed
simultaneous multiple nucleation at the groove as
illustrated in Fig. 1(c). As seen in Fig. 1(d), ΔT at Ptwin= 10−6 for N = 2, 5 and 30 is calculated as 16.6 K, 7.0
K and 2.3 K, respectively. For N = 5, Ptwin becomes3 × 10−6 at ΔT = 7.0 K, which is 100 times the value
at ΔT = 6.9 K. This means that a difference of 0.1 K in
ΔT significantly influences the twinning probability.
In summary, we showed that preferential twin
nucleation in InSb occurs at the bottom of grainboundary grooves.
References[1] M.G. Tsoutsouva, T. Riberi-Béridot, G. Regula, G. Reinhart, J.
Baruchel, F. Guittonneau, L. Barrallier, and N. Mangelinck-Noël,Acta Mater. 115, 210 (2016).
[2] K. Fujiwara, R. Maeda, K. Maeda, and H. Morito, Scr. Mater.
133, 65 (2017).
[3] T. Duffar and A. Nadri, Scr. Mater. 62, 955 (2010).
[4] K. Shiga, A. Takahashi, L.-C. Chuang, K. Maeda, H. Morito,
and K. Fujiwara, J. Crystal Growth 577, 126403 (2022).

Fig. 1 (a) Snapshots of the crystal/melt interface of InSb, (b) schematic illustration of twin boundary formation at the groove,(c) twinning model at the groove, and (d) calculating results of twin nucleation probability.

Kozo Fujiwara (Crystal Physics Research Laboratory)
E-mail: kozo.fujiwara.c6@tohoku.ac.jp
URL: http://www.imr.tohoku.ac.jp/en/about/divisions-and-centers/research-division/02.html

IMR KINKEN Research Highlights 2022

27

Electronic Materials

Study of Strong Magnon-Magnon Coupling in High
Magnetic FieldL

ight-matter objects with strong coupling interactions provide a unique platform for studying quantum vacuum
phenomena. The mode-mode interaction of magnons can be a good model for such strong coupling systems.
One of the unique features of this system is the tuning of the modes using strong magnetic fields. A THz spectrometer
combined with a compact pulsed magnetic field generator enables systematic investigation of such systems.
The interaction between matter and light canbe enhanced in condensed matter systems bystrong many-body correlations, which couple alarge number of dipolar moments with light. Owing
to this enhancement, the interaction between lightand matter may be as large as the frequency of thelight itself, and such a state is called an ultra-strong
coupling regime. In this area, the anti-resonantinteraction is expected to be non-negligible.
However, research on these systems is limited. Oneof the difficulties is finding a system with dominantanti-resonant interactions. In addition, theinteractions must be tuned experimentally.
Recently, we found that the canted
antiferromagnet YFeO3 is a good model material forsuch a strong coupling system, based on terahertz
magneto-spectroscopy in a strong magnetic field[1]. The advantage of this system is that the vacuum
Rabi splitting and vacuum Bloch-Siegert shift canbe tuned by a magnetic field. In this study, themagnons, especially the coupling between different
modes in YFeO3, were experimentally investigatedusing THz time-domain magneto-spectroscopy.
Two unique experimental techniques werecombined, namely single-shot THz detection and atabletop 30T pulse high magnetic field generator.
The tabletop magnet was developed by the
Magnetism Research Division of the Institute forMaterials Research. It can generate 30T by
combining a small capacitor bank power supply
and a mini coil. Unlike THz spectrometers that use
large superconducting magnets, it has theadvantage of being able to use direct optics that areneeded for high precision THz spectroscopy. An
overview of the instrument is shown in Fig. 1.
YFeO3 exhibited an antiferromagnetic structurewith a propagation vector along the a-axis. The
weak ferromagnetic component is caused by thesmall canting along the c-axis.
We found that two peaks with different splitting
and intensity ratio appeared when the magnetic
field was tilted from the c-axis. These two peaks,
termed the upper and lower modes, are caused by
Hiroyuki Nojiri (Magnetism Research Laboratory)
E-mail: hiroyuki.nojiri.e8@tohoku.ac.jp
URL: http://www.hfpm.imr.tohoku.ac.jp

28

IMR KINKEN Research Highlights 2022

Fig. 1 Schematic view of the table top magnet

the hybridization of quasi-ferromagnetic and quasiantiferromagnetic modes This major behavior of theanti-crossing can be reproduced by the LandauLifshitz-Gilbert equation except for the anomalous
large redshift found in the upper frequency mode.
Specifically, the frequency of the upper mode issmaller than that of the quasi-antiferromagnetic
mode. This shift is the direct consequence of thecounter-rotating term.
The full features of the spectra can be
reproduced by the Hopfield-like quantum
mechanical Hamiltonian with variable co-rotating
and counter-rotating coupling strength. We foundthat the counter-rotating term is dominant, and thesimple rotating wave approximation breaks down in
the present system. As a result, an exotic behavior
such as two-modes vacuum squeezing of theground state is realized.
References[1] T. Makihara et al., Nat. Commun. 12, 3115 (2021).

IMR KINKEN Research Highlights 2022

Compact Three-Dimensional Magnetic-Field Sensor

Magnetic-field sensing in three-dimensional (3D) space is one of the essential technologies in automatic
vehicle and robotics. We have succeeded in detection of the 3D magnetic-field vectors with a planar-typesingle Fe-Sn device, where anomalous Hall effect, anisotropic magnetoresistance, and unidirectional
magnetoresistance are complementarily functionalized. Demonstration of a compact 3D sensor will contributeto the future of the Internet-of-Things.
Some nanocrystalline or amorphous metalalloys exhibit significant electronic and magnetic
properties, as exemplified in high permeability
magnets. In this study, we successfully demonstrated
three-dimensional (3D) magnetic-field sensing in
the nanocrystalline ferromagnetic Fe-Sn thin-film
device. Thanks to the use of non-toxic elements anda simple device structure, environmental-friendly
and compact 3D sensors based on Fe-Sn films canbe implemented for use in various devices.
The demand of magnetic-field sensing
technique is increasing in the developing internetof-things (IoT) society. In particular, 3D detection of
the magnetic-field vector (H) is highly desirable for
automatic control of objects by determining theirposition, velocity, and rotation angle [Fig. 1(a)].
Commercially available magnetic sensors such as
semiconductor Hall sensors or magnetoresistancesensors generate the output signal against thescalar quantity of H along a principal direction.
Therefore, to detect the 3D direction of H, it isnecessary to place three magnetic sensors along
the X, Y, and Z directions. By contrast, a planar-typesingle Fe-Sn Hall sensor [Fig. 1(b)] can detect the
3D direction of H [1]. A large anomalous Hall effect(AHE) is utilized for detecting the polar angle (θ H) of
H in a similar manner to a semiconductor device[2,3]. The magnetic Fe-Sn sensor has an additional
ability not seen in semiconductor devices, to detect
the magnetic field through the anisotropic
magnetoresistance (AMR) and an unexpectedly
large unidirectional magnetoresistance (UMR),
where the AMR and UMR show 180o and 360o
periodic functions of azimuthal angle (φ H) of H,
respectively. By combining AHE, AMR, and UMR,
individual and simultaneous determination of the 3D
direction of H in orthogonal rotation wasdemonstrated, as shown in Fig. 1(c).
Further
improvementofthesensing
performance is expected by Fermi-level tuning via
impurity doping [4] or device structure design [5].
Determination of H in the 3D space with a planartype simple device geometry would accelerate theminiaturization of 3D magnetic sensors, which would

(a)

(b)

z

H
x

y
M
I = I0sinωt

(c)
Z
H
X

Y

Fig. 1 (a) Schematic of the device operation. (b) Schematicof the planar-type Fe-Sn Hall-bar sensor, where Hall
resistance (R H), anisotropic magnetoresistance (RAMR),
and unidirectional magnetoresistance (R UMR), which
depends on magnetization vector (M), aresimultaneously measured for determination of thevector (H(θ H,φ H)). (c) Demonstration of detection ofmagnetic-field angles θ H and φ H.

in turn contribute to the development of IoT devices
composed of large numbers of sensors.
References[1] J. Shiogai, K. Fujiwara, T. Nojima, and A. Tsukazaki, Commun.
Mater. 2, 102 (2021).
[2] Y. Satake, K. Fujiwara, J. Shiogai, T. Seki, and A. Tsukazaki,
Sci. Rep. 9, 3282 (2019).
[3] J. Shiogai, Z. Jin, Y. Satake, K. Fujiwara, and A. Tsukazaki,
Appl. Phys. Express 12, 123001 (2019).
[4] K. Fujiwara, Y. Satake, J. Shiogai, and A. Tsukazaki, APL
Materials 7, 111103 (2019).
[5] J. Shiogai, Z. Jin, Y. Satake, K. Fujiwara, and A. Tsukazaki,
Jpn. J. Appl. Phys., (2021) in press.

Junichi Shiogai (Low Temperature Physics Research Laboratory)
E-mail: junichi.shiogai@tohoku.ac.jp
URL: http://mu.imr.tohoku.ac.jp/index_en.html

IMR KINKEN Research Highlights 2022

29

Electronic Materials

Charge Ordering and π–d Interaction in Electron-Doped 3/4-Filling
Molecular System α”-(BEDT-TTF)2Rb2x Co(SCN)4 (x = 0.6)

Charge ordering and band-filling control have been intensively investigated in strongly correlated electron
systems. In organic molecular systems, however, band-filling control is usually difficult and is not yet fully
understood. Here, we describe a new two-dimensional organic crystal with an intermediate value of band filling.
Transport and infrared optical measurements revealed that this compound transits to a charge-ordered state at
100 K, which is the lowest among the isomorphic compounds with commensurate values of band filling.
Two-dimensional organic molecular crystals(BEDT-TTF)2X, where BEDT-TTF is bis(ethylenedithio)
tetrathiafulvalene and X is an anion, often show
insulating states due to the electron correlation. Since
X is typically monovalent, the hole filling of the BEDTTTF molecular band becomes quarter-filled andcharge ordering is expected to emerge. Among suchmaterials, θ-type crystals θ-(BEDT-TTF)2AM(SCN)4(where A is an alkaline ion, and M is a divalent metalion) are well studied charge-ordering systems.
In charge-ordering systems, the band filling is
an important parameter for the stability of chargeordering. Thus, filling control by chemical doping is
the predominant method for studying the chargeorder e.g., in transition-metal oxides. However, thismethod is difficult for organic molecular systems,
since the impurities tend to be excluded from thecrystal during the crystal growing procedure. Only a
few crystals with an intermediate band-filling value
are known. α”-(BEDT-TTF)2AM(SCN)4 system (AM =K1.4Co (α”-K1.4Co), CsHg (α”-CsHg)) is one of thecandidates for studying the band-filling control ofmolecular crystals. The above two compounds transit
from metal to insulator at low temperatures. The
transition temperature of α”-K1.4Co is lower than thatof α”-CsHg, suggesting the instability of chargeordering. A compound with a band-filling valueintermediate between these is desirable.
In the course of studying the charge ordering inorganic molecular systems, we found a newcompoundα”-(BEDT-TTF)2Rb2xCo(SCN)4(α’’Rb2x Co) [1]. From the x-ray diffraction and energy
dispersive x-ray spectroscopy measurements, Rb
site occupancy x was determined to be about 0.6(Fig.1(a)). Thus, we found that α’’-Rb1.2Co has anintermediate band-filling value between those of α”K1.4Co and α”-CsHg and an intermediate dihedral
angle (θ) between two adjacent molecules (see. Fig.
1(b)). This compound also shows metal-insulatortransition at about 100 K (Fig.1(c)), similar to theabove two compounds. However, the transition
temperature is lower. This can be expected from theFig. 1 (a) Crystal structure and (b) two-dimensional BEDTTTF layer of α’’-Rb1.2Co. Temperature-dependence of(c) resistivity and (d) ν 27 vibrational mode.

incommensurate filling of α’’-Rb1.2Co and nearlycommensurate α”-K1.4Co.
In order to obtain evidence of the chargeordering, we measured the infrared optical spectra.
In the wavenumber region of 1400-1550 cm-1,
vibrational mode ν 27 can be observed for the BEDTTTF molecule. The peak frequency of the ν 27 mode isvery sensitive to the valence and often used in orderto detect the charge states of the BEDT-TTF molecule.
As shown in Fig.1(d), a splitting of the valence wasfound. This suggests that the charge-orderingtransition occurs at about 100 K.
Reference [1] also discusses the existence ofthe π-d interaction using magnetic and magnetodielectric properties.
References[1] S. Iguchi, S. Yamada, R. Kobayashi, K. Morita, Y. Kudo, M.
Kurosu, N. Yoneyama, Y. Ikemoto, T. Moriwaki, and T. Sasaki, J.
Phys. Soc. Jpn. 90, 074701 (2021).

Satoshi Iguchi (Low Temperature Condensed State Physics Research Laboratory)
E-mail: satoshi.iguchi.c8@tohoku.ac.jp
URL: http://cond-phys.imr.tohoku.ac.jp/index_e.html

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IMR KINKEN Research Highlights 2022

Superconducting State with Pair Density Wave inLa1.87Sr0.13Cu0.99Fe0.01O4

T

he pair density wave (PDW) order, which is an intertwined state among the spin, charge density, andsuperconducting order parameters, has attracted attention in connection with superconductivity in cuprate oxides.
To clarify the necessary conditions for the formation of PDW, we performed resonance X-ray scattering measurements
on La1.87Sr0.13Cu0.99Fe0.01O4. The signature of PDW appeared when the correlation length of the charge density
wave exceeded ~ 30 Å upon cooling, suggesting the crucial role of charge correlation in the formation of PDW.
Since the discovery of high-temperature (highTc) superconductivity (HTSC) in cuprate oxides,
tremendous progress has been made in the field ofstrongly correlated electron systems. One recent
area of interest regarding HTSCs is the pair density
wave (PDW), which forms the spatially modulated
spin and charge density (SDW and CDW) and theorder parameter of the Cooper pair on the CuO2
planes. To experimentally identify the PDW order,
the appearance of anisotropic (two-dimensional)
superconductivity and the coexistence of spin andcharge density wave orders (Fig. 1) need to beclarified [1]. A small amount of Fe substitution in La2xSrxCuO4 (LSCO) suppresses the superconducting
transition temperature (Tc) and enhances the stabilityof SDW and CDW orders [2]. Therefore, Fesubstituted LSCO is a suitable system to study theintertwining of complex orders in high-Tc cuprates.
We performed resistivity and resonant soft
X-ray scattering (RSXS) experiments on a highquality single crystal of La1.87Sr0.13Cu0.99Fe0.01O4(LSCFO). As shown in Fig. 1, anisotropic resistivity
behavior was observed at temperatures between~11 K (T2) and ~32 K (T1). Therefore, PDW fluctuations
potentially existed between T1 and T2. Furthermore,
we observed the signal from the CDW order using
RSXS measurements at low temperatures (Fig. 2).
The CDW peak grew upon cooling, and the intensity
tended to increase more markedly once the SDW
order appeared at a low temperature. Thus, thedevelopment of CDWs can be enhanced by SDWs
through intertwining. The correlation length (ξ ch) of
the CDW order evaluated from the peak width
increased with decreasing temperature below 70 K.
The ξ ch reached ~30 Å, which is approximately
eight times the in-plane lattice constant at T1, andremained constant. From the above results, it was
found that the signature of PDW starts to appear
when ξ ch grows over ~ 30 Å, suggesting the crucialrole of charge correlation in the formation of the
PDW order in LSCFO. RSXS measurements on othercopper oxides are expected to reveal the ubiquitousFig. 1 Temperature dependence of the anisotropic
resistivity [1]. ρab and ρc represent the in-plane and outof-plane resistivity.

Fig. 2 Signals from charge density waves observed byresonant soft X-ray scattering experiments at various
temperatures [1].

nature of PDW in high-Tc cuprates and the universal
relationship between CDW and PDW in cuprateoxides [3, 4].
References[1] H. Huang, S.-J. Lee, Y. Ikeda, T. Taniguchi, M. Takahama, C.C. Kao, M. Fujita, and J.-S. Lee, Phys. Rev. Lett. 126, 167001(2021).
[2] M. Fujita, M. Enoki, and K. Yamada, J. Phys. Chem. Solids 69,
3167 (2008).
[3] S. Asano, K. Ishii, D. Matsumura, K. Kudo, T. Taniguchi, S.
Saito. T. Sunohara, T. Kawamata, Y. Koike, and M. Fujita, Phys.
Rev. B 104, 214504 (2021).
[4] H. Yamase, Y. Sakurai, M. Fujita, S. Wakimoto, and K. Yamada,Nat. Commun. 12, 2223 (2021).

Masaki Fujita (Quantum Beam Materials Physics Research Laboratory)
E-mail: masaki.fujita.b5@tohoku.ac.jp
URL: http://qblab.imr.tohoku.ac.jp/index-e.html

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Electronic Materials

Magnetization Control by Angular Momentum Transfer from
Surface Acoustic Wave to Ferromagnetic Spin MomentsIn solids, there are various forms of angular momentum. Electrons have spin and orbital angular momenta. The
circular motion of atoms can be viewed as the angular momentum of phonons. The interconversion between
different forms of angular momentum is useful for spin-based information processing. Here, we demonstratethat the phonon angular momentum of surface acoustic waves can control magnetization by means of thephononic-to-electronic conversion of angular momentum in a Ni/LiNbO3 hybrid device.
The injection of spin current is thought to be an
efficient way of magnetization control in a nanoscale
ferromagnet. Although rotational symmetry is,strictly speaking, broken in the magnet, the sum ofangular momentum is nearly preserved over a shortperiod, and it is transferred from the conduction
electrons to magnetic moments in the injection
process. Whether or not phononic angularmomentum transfer is also effective for magnetization
control is an area of interest.
In this work, we show that the phonon angularmomentum of a surface acoustic wave can control
the magnetization in a Ni/LiNbO3 hybrid device. A
surface acoustic wave is the acoustic wave
propagating on a surface. It has ellipsoidal
polarization, and the rotational direction is reversed
when the wave vector is reversed. Therefore, thewave vector and angular momentum are closely
coupled in the surface acoustic wave.
We fabricated a Ni/LiNbO3 hybrid device, inwhich surface acoustic waves propagate on the Ni
ferromagnet (Fig. 1). The Ni film has an elongatedshape, and therefore the magnetization tends toalign along the elongated direction at zero magnetic
field owing to the shape anisotropy, while there is
still up/down degeneracy. In order to demonstrate
the magnetization control, we applied a strong
magnetic field perpendicular to the elongateddirection and decreased it to zero while applying
surface acoustic waves. When the angularmomentum of the surface acoustic wave is effectivelytransferred to the Ni ferromagnet, the magnetization
direction after the application of the perpendicularmagnetic field should be controlled by the angularmomentum of the surface acoustic wave coupled to
the wave vector (Fig. 2). We observed that themagnetization after this process depended on the
wave vector of the surface acoustic wave.
The present results experimentally demonstrate
an important functionality of angular momentum,
the conversion to ferromagnetic spin moments,
which shows the validity of phonon angularFig. 1 An optical micrograph of the surface acoustic wave
device used in this work [1].

Fig. 2 Schematic illustrations of the magnetization control
by angular momentum of surface acoustic wave [1].

momentum. The control of magnetization by thesurface acoustic wave is useful to transfer the
information carried by the microwave signal to themagnetic storage. In this sense, it is expected toprovide a bridge between telecommunication
technology and spintronics because surface
acoustic devices are indispensable in contemporary
telecommunications technology.
References[1] R. Sasaki, Y. Nii, Y. Onose, Nat. Commun. 12, 2599 (2021).

Yoshinori Onose (Quantum Functional Materials Physics Research Laboratory)
E-mail: yoshinori.onose.b4@tohoku.ac.jp
URL: http://www.imr.tohoku.ac.jp/en/about/divisions-and-centers/research-division/08.html

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IMR KINKEN Research Highlights 2022

Circular Polarized Light Induced Zero-Bias Photocurrent in
Chiral 2D Organic-Inorganic Hybrid Perovskites

Noncentrosymmetry opens the door to a large variety of advanced properties in functional materials, such as
ferroelectricity and nonlinear optics. In this study, a chirality-dependent circular photogalvanic effect, which isa zero-bias photocurrent-generating phenomenon by circular polarized light, was successfully discovered forthe first time in a pair of chiral 2D organic-inorganic hybrid perovskites.

Breaking spatial inversion symmetry in materials
leads to opportunities for the development of novel
functionalities [1]. In particular, noncentrosymmetryin optoelectronics presents potential applications in
the field of material science [2,3].
The circular photogalvanic effect (CPGE) is a
novel optoelectronic phenomenon induced innoncentrosymmetric materials, in which a helicitydependent steady-state photocurrent is generated
by irradiation of circularly polarized light (CPL)
without applying an external bias voltage. Although
the CPGE has attracted growing interest as anefficient technique for the detection of novel chiralelectronic states in opaque samples such as Weyl
semimetals, the chirality dependence of CPGE has
not been confirmed so far in enantiomorphic
materials. This is due to the difficulty of designingchiral inorganic materials composed of heavy atoms
with strong spin-orbit coupling (SOC). SOC in chiralsystems affording a spin-splitting band is necessary
for the induction of the CPGE.
To solve this issue, we have utilized twodimensional(2D)
organic-inorganic
hybridperovskites (OIHPs), introducing chiral organic
cations between inorganic lead-iodide layers withstrong SOC. Here, a pair of chiral 2D-OIHP lead
iodides with space groups of P41(3)212 were

investigated.
Under CPL exposure, the CPL helicity
dependent zero-bias photocurrent, which is afeature of CPGE, was observed. Furthermore, theCPGE photocurrent apparently showed sign reversal
depending on the chirality of the materials for the
first time. This could be elucidated by the radial spin
texture formed by “spin-momentum locking” ink-space for a chiral system. From the microscopic
viewpoint, the chiral 2D OIHP lead(II) halide-basedmaterial is a promising platform for opto-spintronics
applications.
References[1] K. Taniguchi, M. Nishio, N. Abe, P.-J. Huang, S. Kimura, T.
Arima, and H. Miyasaka, Angew. Chem. Int. Ed. 60, 14350(2021).
[2] P.-J. Huang, K. Taniguchi, M. Shigefuji, T. Kobayashi, M.
Matsubara, T. Sasagawa, H. Sato, and H. Miyasaka, Adv.
Mater. 33, 2008611 (2021).
[3] P.-J. Huang, K. Taniguchi, and H. Miyasaka, J. Am. Chem.
Soc. 141, 14520 (2019).

Fig. 1 Schematics of measurement configuration and photocurrent (j) versus quarter-wave plate (QWP) angle for R- andS-enantiomers.

Po-Jung Huang, Kouji Taniguchi, and Hitoshi Miyasaka (Solid-State Metal-Complex Chemistry Research Laboratory)
E-mail: huang.po.jung.c8@tohoku.ac.jp, koji.taniguchi.e2@tohoku.ac.jp, hitoshi.miyasaka.e7@tohoku.ac.jp
URL: http://www.miyasaka-lab.imr.tohoku.ac.jp/cn5/HOME-Eng.html

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Electronic Materials

Chiral Crystallization Assisted by Chiral Near-Field Force

It has been previously reported that giant crystal enantiomeric excess can be obtained by inducing chiral

crystallization of NaClO3 from an Au triangle trimer plasmonic nanostructure excited by a circularly polarized laser.
However, its mechanism remains unclear. We showed that chiral optical force originating from the strong superchiralplasmonic near-field of the plasmonic nanostructure enantioselectively influences the kinetics of chiral nucleation.
Recent progress in plasmonics has shown thatthe chiral near-field generated by the excitation of
localized surface plasmon resonance of metal
nanoparticles can significantly boost intrinsicallyweak chiral light-matter interaction between circularly
polarized light and chiral matter [1]. Recently, it has
been discovered that chiral crystallization of NaClO3
from a Au triangle trimer plasmonic nanostructure
excited by a circularly polarized laser (CPL) yields
the giant crystal enantiomeric excess, which cannot
be achieved only by CPL [2, 3] (Fig. 1). However, themechanism leading to the giant crystal enantiomeric
excess remains unclear. We have performed anumerical analysis of the optical chirality density,
which is a measure of chirality in an electromagnetic
field, in the plasmonic near-field generated by CPL
irradiation to the Au nanostructure to evaluate thecontribution of the chiral optical force exerted on
NaClO3 chiral crystalline pre-critical clusters [4]. The
analysis showed that a strong enhancement of
optical chirality density, approximately 40-fold that ofCPL, can be observed locally in the nanogap at thecenter of the Au nanostructure on a scale of a few
tens of nanometers. This ‘chiral hotspot’ of theplasmonic near-field was found to be capable ofproducing the enantioselective chiral optical force,
which acts on the chiral crystalline clusters. The
magnitude of the chiral optical force was found to becomparable to that seen in previous experiments onlaser-trapping-induced crystallization [5], where
crystallization was induced by optical trapping of
crystalline clusters, even in unsaturated solutions.
These analyses indicate that enantioselective chirally
biased diffusion of the chiral crystalline clusters
induced by the chiral optical force can occur. The
diffusion may cause fluctuations in the frequency of
attachment of chiral building units onto crystal nuclei
or in the concentration of chiral building units aroundthe nuclei between both enantiomorphs, leading to
the giant chiral enantiomeric excess.

Fig. 1 Schematic of the NaClO3 chiral crystallization
experiment using a triangle trimer plasmonic nanostructure,
which yielded a giant crystal enantiomeric excess [2].

Fig. 2 Optical chirality density distribution analyzed by finitedifference time-domain method (upper). OC and OCCPL
represents optical chirality density of near-field and ofincident CPL, respectively. Enantioselective optical potential
exerted on chiral nanoparticles (lower). κ is chirality
parameter of chiral particle and r is radius of the particle.
T. Sugiyama, J. Phys. Chem. Lett. 11, 4422 (2020).
[3] H. Niinomi, T. Sugiyama, M. Tagawa, K. Murayama, S. Harada
and T. Ujihara, CrystEngComm 18, 7441 (2016).
[4] H. Niinomi, T. Sugiyama, A.-C. Cheng, M. Tagawa, T. Ujihara,

References

H. Y. Yoshikawa, R. Kawamura, N. Nozawa, J.T. Okada and S.

[1] M. Hentschel, M. Schäferling, X. Duan, H. Giessen, and N. Liu,

Uda, J. Phys. Chem. C 125, 6209 (2021).

Sci. Adv. 3, e1602735 (2017).
[2] A. C. Cheng, H. Niinomi, T. Omatsu, S. Ishida, K. Sasaki, andHiromasa Niinomi (Crystal Chemistry Research Laboratory)
E-mail: hiromasa.niinomi.b2@tohoku.ac.jp
URL: http://www.uda-lab.imr.tohoku.ac.jp/index-e.html

34

IMR KINKEN Research Highlights 2022

[5] T. Sugiyama, K. Yuyama and H. Masuhara, Acc. Chem. Res.
45, 1946 (2012).

IMR KINKEN Research Highlights 2022

Field-Induced Superconductivity in UTe2 with Spin-Triplet StateF

ield-induced superconductivity was observed in the spin-triplet superconductor UTe2 when the pressure
was tuned above the critical pressure. The magnetic ordered phase at low field collapsed above 10T, andsuperconductivity abruptly appeared, continuing above our highest field of 28T in the spin-polarized state.
15

R (m )

4K
10

5

(a)
UTe2
H || b-axis
1.45 GPa

2K

1K

0
0

10

30

H (T)

20

30
(b)

20

SC

H (T)

Unconventional superconductivity in UTe2 is ofcurrent interest in condensed matter physics; six
papers related to UTe2 were selected as “Most cited
10 articles in 2020” in JPSJ. A highlight of UTe2 isthe emergence of multiple superconducting phases
under pressure and magnetic fields owing to thespin and orbital degrees of freedom, indicating thespin-triplet state. Spin-triplet superconductivity is
expected to be topological superconductivity. Thus
UTe2 also provides a good opportunity to study“bulk” topological superconductivity.
Another important characteristic of UTe2 is thelarge upper critical field, Hc2, which is much higher
than the so-called “Pauli limit” expected from theweak-coupling BCS theory. Therefore, an
unconventional
superconducting
mechanism,
namely, the spin-triplet state, is in effect. In particular,when the field is applied along the b-axis in theorthorhombic
structure,
field-reentrant
superconductivity is observed up to an extremely
high field of 35T. This field-robust superconductivity
has also been studied through spin susceptibility
using NMR to clarify the superconducting
mechanism from a microscopic point of view [1].
Low-temperature magnetization measurements [2]revealed that the lower critical field Hc1 is also
unusually anisotropic compared to the anisotropy of
Hc2, implying a peculiar vortex state.
Here,
we
present
another
unusualsuperconducting property of the UTe2. Figure 1(a)shows the magnetoresistance of the H || b-axis in
UTe2 when the pressure was tuned just above thecritical pressure Pc. No superconductivity isdetected at zero field, whereas a magneticallyordered phase (MO) appears. Surprisingly, when ahigh magnetic field above 10T was applied, fieldinduced superconductivity was detected. The H-T
phase diagram is shown in Fig. 1(b). At high fields,
the magnetically ordered phase, most likely due toantiferromagnetism, was suppressed, and then the
superconducting phase appeared in the spinpolarized state. These results are compatible with aspin-triplet scenario. Note that the superconductivity
in the spin-polarized state resembles that observed
above Hm~40T for H || [011] at ambient pressure.

10

0
0

MO

WMO
5
T (K)

10

Fig. 1 (a) Magnetoresistance for H || b-axis at 1.45GPa justabove the critical pressure in UTe2. Field-induced
superconductivity was detected at 1K and 2K. (b)corresponding H-T phase diagram. SC, MO and WMO
denote superconductivity, magnetic order and weakly
magnetic order, respectively [3].

The interplay between the different fluctuations may
play a crucial role.
This work was done in collaboration with CEAGrenoble, LNCMI, High field lab at IMR and Oarai
center.
References[1] G. Nakamine, K. Kinjo, S. Kitagawa, K. Ishida, Y. Tokunaga, H.
Sakai, S. Kambe, A. Nakamura, Y. Shimizu, Y. Homma, D. Li, F.
Honda, and D. Aoki, Phys. Rev. B 103, L100503 (2021).
[2] C. Paulsen, G. Knebel, G. Lapertot, D. Braithwaite, A. Pourret,
D. Aoki, F. Hardy, J. Flouquet, and J. P. Brison, Phys. Rev. B
103, L180501 (2021).
[3] D. Aoki, M. Kimata, Y. J. Sato, G. Knebel, F. Honda, A.
Nakamura, D. Li, Y. Homma, Y. Shimizu, W. Knafo, D.
Braithwaite, M. Valiska, A. Pourret, J.-P. Brison, and J. Flouquet,
J. Phys. Soc. Jpn. 90, 074705 (2021).

Dai Aoki (Actinide Materials Science Research Laboratory)
E-mail: dai.aoki.c2@tohoku.ac.jp
URL: http://www.imr.tohoku.ac.jp/en/about/divisions-and-centers/research-division/25.html

IMR KINKEN Research Highlights 2022

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Electronic Materials

Effect of Ta Substitution on the Synthesis of (K,Na)(Nb,Ta)O3
Powders by Hydrothermal ReactionTa-substituted (K,Na)NbO3 powders with K-rich composition across a polymorphic phase boundary weresynthesized at 200°C by a hydrothermal method. It was found that the synthesis behavior of (K,Na)(Nb,Ta)O3
is strongly dependent on the combination of alkaline solution and raw powder.
The morphological control of ferroelectric powders
with a perovskite-type structure has been widely
investigated as an important technique for developing
high-performance materials and devices. Pb(Zr,Ti)O3 isthe most widely investigated ferroelectrics material
because of its excellent electrical properties. The best
performance of Pb(Zr,Ti)O3 is achieved at themorphotropic phase boundary (MPB), a discontinuouschange in the crystalline phase from a tetragonal phase
to a rhombohedral one.9) However, due to the toxicity oflead in the environment and the human body, there isan ongoing demand for lead-free ferroelectrics. (K,Na)
NbO3 has attracted much attention as a promising
candidate to replace Pb(Zr,Ti)O3. In this study, we
synthesized (K,Na)(Nb,Ta)O3 powders with K-richcomposition by the hydrothermal method andinvestigated their crystal structure and microstructure.
In particular, we examined the synthesis behavior of(K,Na)(Nb,Ta)O3 powders from the viewpoints of the
combination of the alkaline solutions and raw powders[1].
Figures 1(a)-1(g) show Scanning Electron
Microscope (SEM) images of the powders obtained in
the range of C = 0-1. As seen, the morphology of
powder changed from polymorphic to square at C =0.3, and a smooth powder surface was observed. Thisobservation suggests that the {100}c planes of the oxide
become energetically stable as Ta content increases.
In addition, the size of the square-shaped powder
decreased with increasing nominal composition. SEM
images of Nb2O5 and Ta2O5 powders are shown in Fig.
1(h) and 1(i). Rod-shaped particles were observed in
Nb2O5, while Ta2O5 particles had round shapes. Thesemorphologies were significantly different from thoseobserved with (K,Na)(Nb,Ta)O3. In addition, the particle
size of Ta2O5 powder was much smaller than that of
Nb2O5 powder. Therefore, it is considered that theparticle size of the (K,Na)(Nb,Ta)O3 powder decreased
with increasing the nominal composition.
Figure 2 summarizes the volume fraction of
perovskite phase estimated from the intensity ratio. As
shown here, the synthesis behaviors of stoichiometric
KOH-Nb2O5, NaOH-Nb2O5, KOH-Ta2O5, and NaOHTa2O5 systems indicated that the formation of anFig. 1 SEM images of (a)-(g) (K,Na)(Nb,Ta)O3, (h) Nb2O5,
and (i) Ta2O5 powders.

Fig. 2 Synthesis time dependence of volume fraction of
perovskite phase: (a) KOH-Nb2O5, (b) NaOH-Nb2O5,(c) KOH-Ta2O5, and (d) NaOH-Ta2O5.

intermediate phase is the key factor to obtain aperovskite single-phase powder.
References[1] S. Sano, T. Shiraishi, T. Kiguchi, and T.J. Konno, J. Ceram. Soc.
Jpn. 129, 365 (2021).

Toyohiko J. Konno (Materials Science of Non-Stoichiometric Compounds Research Laboratory)
E-mail: tjkonno@tohoku.ac.jp
URL: http://www.imr.tohoku.ac.jp/en/about/divisions-and-centers/research-division/26.html

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IMR KINKEN Research Highlights 2022

Tailorable Magnet Creation in a Paramagnetic Metal–Organic
Framework Depending on Guest Species

Creation of magnets from nonmagnetic materials induced by external stimuli holds potential applications as

magnetic switches, memories, and sensors, yet study of guest-responsive porous magnets remains rare. We
demonstrated an electronic-state-flexible paramagnetic metal–organic framework that could change to either
the ferrimagnetic or antiferromagnetic phase by accommodating different guest molecules in the lattice.

Magnetic metal–organic frameworks (MOFs), in
which one or a few paramagnetic metal nodes andradical organic ligands are used to construct magnetic
components, have sparked tremendous interest as
switchable magnets due to their high degree ofdesignability and structural diversity. Guest moleculesthat perturb the crystal lattice of the framework arecapable of magnetic modulation in magnetic MOFs;
however, guest-driven magnetic ground state (magnetic
phase) changes with flexible lattices are surprisingly
scarce.
In this study, we synthesized a paramagnetic guestfree framework, [{Ru2(2,4-F2PhCO2)4}2 TCNQ(OEt)2] (1;2,4-F2PhCO2 - = 2,4-difluorobenzoate; TCNQ(EtO)2 =2,5-diethoxy-7,7,8,8-tetracyanoquinodimethane)(Fig.
1a), which consists of two [Ru2(2,4-F2PhCO2)4] units aselectron donors (D) and one TCNQ(OEt)2 moiety as an
acceptor (A) [1]. Compound 1 exhibited a thermallyinduced electronic state modulation at 384 K between a
two-electron-transferred state of [D+-A2--D+] ∞ (T < 384K) and a one-electron-transferred state of [D-A- -D+] ∞ (T> 384 K), indicating flexible charge states towards theexternal stimuli.
Furthermore, the crystal structure of 1 was porousand flexible. Several guest molecules such as benzene(PhH), p-xylene (PX), dichloromethane (DCM),
1,2-dichloroethane (DCE), and carbon disulfide (CS2),
could be accommodated into 1 to obtain solvatedcompounds (1-solv) concomitant with an intralatticeelectron transfer from A2- to one of the D+ moieties toform a [D-A- -D+] ∞ repeating unit and a structuralmodulation. This change in charge distribution allowed
for intralayer ferrimagnetic ordering with spin sets of S =3/2 (↑), 1 (↑), and 1/2 (↓) for D+, D, and A-, respectively.
Consequently, 1-solv with PhH, PX, DCM, and DCE
became a ferrimagnet with interlayer ferromagnetic
interactions at Curie temperatures (TC) ranging from 70
to 92 K (Fig. 1b); meanwhile, with CS2, it became an
antiferromagnet with a Neel temperature (TN) of 78 K,
owing to the presence of interlayer antiferromagnetic
interactions (Fig. 1b). The magnetic ground state offerrimagnet or antiferromagnet was influenced by theinterlayer packing environment.
This work demonstrates an “alchemy for magnets”,
in which bulk magnets are made from a nonmagnetic
material by inserting diamagnetic guest molecules. The
variable magnetism actuated by the electronic state
modulation and structural change not only makes suchstrong electron-correlated MOFs candidates for futureapplication as chemical sensors, but will also inspire thedevelopment of new magnetically and electronicallyfunctional materials.
References[1] J. Zhang, W. Kosaka, H. Sato, and H. Miyasaka, J. Am. Chem. Soc.
143, 7021 (2021).

Fig. 1 (a) Crystal structure of paramagnetic compound 1. (b) Temperature dependence of χ measured at 100 Oe for 1(black), 1-CS2 (blue), 1-DCE (green), 1-DCM (cyan), 1-PhH (red), and 1-PX (orange).

Jun Zhang (Exploratory Research Laboratory)
E-mail: jun.zhang.d2@tohoku.ac.jp
URL: http://www.imr.tohoku.ac.jp/en/about/divisions-and-centers/research-division/33.html

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Research Centers

IMR KINKEN Research Highlights 2022

ResearchResearch Centers

Longitudinal Magnetic Fluctuations Near the Superconducting
Phase in Ferromagnetic Superconductor UGe2
International Research Center for Nuclear Materials and ScienceT

he mechanism of superconductivity emerging in the ferromagnetic state has attracted much attention
because it deviates from the conventional one induced by electron-phonon coupling. We clarified that
longitudinal magnetic fluctuations develop near the superconducting phase in UGe2. Our observation strongly
supports a consensus that superconductivity in ferromagnets is mediated by anisotropic magnetic fluctuations.
The emergence of superconductivity inferromagnets was first observed in UGe2 two
decades ago [1].
In ferromagnets, the Cooper pairs must be
formed on the degeneracy-lifted Fermi surfaces,
which deviates from the conventional theory ofsuperconductivity mediated by the electron-phonon
interaction. Such unusual superconductivity has
previously been theoretically predicted to be
induced by Ising-like magnetic fluctuations [2];however, experimental evidence has been absent in
UGe2.
In UGe2, superconductivity was observed near
the first-order quantum phase transition between
the FM1 and FM2 phases, as shown in Fig. 1. The
first-order line terminates at the critical point (CP) ataround 7 K (a red point). This temperature is low
enough to expect that magnetic fluctuations induced
at the CP would survive even at low temperatures.
However, the corresponding fluctuations have notbeen observed in the previous measurements of thenuclear spin-lattice relaxation rate, 1/T1, using
nuclear magnetic resonance (NMR) [3].
Recently, we performed measurements of thespin-echo decay rate, 1/T2, to clarify a connection
betweensuperconductivity
andmagnetic
fluctuations [4]. The term 1/T1 corresponds to thetransverse magnetic fluctuations against the nuclear
quantization axis, that is, normal to the direction of
the magnetization, while 1/T2 includes thelongitudinal magnetic fluctuations. Figure 1 shows
the pressure dependence of 1/T2 at ~1.6 K. The
result demonstrates that 1/T2 is enhanced near the
first-order line. Absence of such anomaly in 1/T1
suggests that longitudinal magnetic fluctuations
develop near the quantum phase transition.
Remarkably, the enhancement of 1/T2 is not
symmetric but predominant in the high-pressure
FM1 phase. This also supports the connection

Fig. 1 Pressure-temperature phase diagram of UGe2 near
the superconducting (SC) phase (top). Pressure
dependence of 1/T2 (bottom).

betweensuperconductivity
andmagnetic
fluctuations in UGe2, because a realization of bulk
superconductivity has been suspected in the lowpressure FM2 phase. Our study provided a clear
indication that superconductivity is mediated byanisotropic
magnetic
fluctuation
inFM
superconductors.
References[1] S. S. Saxena, P. Agarwal, K. Ahilan, F. M. Grosche, R. K. W.
Haselwimmer, M. J. Steiner, E. Pugh, I. R. Walker, S. R. Julian,
P. Monthoux, G. G. Lonzarich, A. Huxley, I. Sheikin, D.
Braithwaite, and J. Flouquet, Nature 406, 587 (2000).
[2] D. Fay and J. Appel, Phys. Rev. B 22, 3173 (1980).
[3] H. Kotegawa, A. Harada, S. Kawasaki, Y. Kitaoka, Y. Haga, E.

−

Yamamoto, Y. Onuki, K. M. Itoh, E. E. Haller, and H. Harima, J.
Phys. Soc. Jpn. 74, 705 (2005).
[4] Y. Noma, H. Kotegawa, H. Tou, H. Harima, Y. Haga, E.

−

Yamamoto, Y. Onuki, K. M. Itoh, A. Nakamura, Y. Homma, F.
Honda, and D. Aoki, J. Phys. Soc. Jpn. 90, 073707 (2021).

Hisashi Kotegawa (Corresponding Author, Department of Physics, Kobe University)
E-mail: kotegawa@crystal.kobe-u.ac.jp
Yasuyoshi Nagai (Head of International Research Center for Nuclear Materials and Science)
E-mail: yasuyoshi.nagai.e2@tohoku.ac.jp
URL: http://www.imr-oarai.jp/en/40

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IMR KINKEN Research Highlights 2022

Unique Behavior of Martensitic Transformation at LowTemperature in Ti-Ni-Cu Based Shape Memory Alloys
Cooperative Research and Development Center for Advanced Materials

T

he Center contributes to research and development of new materials and their fabrication processes to
explore the possibility of their application as multi-functional materials for future technology, in collaboration
with universities and government organizations. Here, we highlight our recent research on the precursor
phenomena in Ti-Ni-Cu based shape memory alloys at low temperatures.

Fig. 1 The bright field image and selected-area electron
diffraction pattern taken from 111B2 direction at T = 89 K
in Ti48.2Ni41.8Cu10.0 alloy.
I phase trans.

0.360
0.350

position, ζThethermodynamics
ofmartensitic
transformation and mechanical property at low
temperatures in Ti-Ni based shape memory alloys
has been reported previously [1-3]. A uniquestructural phase transition called “the CommensurateIncommensurate (C-IC) transition” exists at low
temperatures in Ti-Ni-based alloys [4], and wereported that the existence of the C-IC transition for
the first time in Ti-Ni-Cu based alloys [1]. Here, we
introduce the characteristics of C-IC transition bytransmission electron microscope (TEM) observationin Ti-Ni-Cu based alloys.
The
B2/B19martensitic
transformation
temperature decreases with increasing Ni content. In
Ti50.0-x Ni40.0+x Cu10.0 alloys with Ni compositions overx = 1.4, a pre-martensitic “intermediate” phase was
detected by thermoanalysis measurements [1]. Here,the C phase in the C-IC transition corresponds to theIntermediate (I) phase. In the bright field image andselected-area diffraction pattern (SADP) obtained in
the 111B2 direction, the diffraction point derived fromthe B19 phase was observed at T = 87K and the B19
martensite plate was confirmed (Fig. 1).
The SADPs were observed at each temperaturefrom the region shown in Fig. 1, and the temperaturedependence of the diffraction point (0ζζ) due todiffuse scattering was investigated. Figure 2 shows
the temperature dependence of the diffuse scattering
position (0ζζ) of the x = 1.8 alloy. It was clarified thatthe intensity of (0ζζ) decreases with increasing
temperature. On the low temperature side, theposition of diffuse scattering is ζ ≈ 1/3, and it wasclarified that the position of diffuse scattering deviatesfrom 1/3 as the temperature rises. This tendency is ingood agreement with previous studies [2], and it isconsidered that the C-IC transition occurs even at
low temperature in Ni-rich Ti-Ni-Cu based alloy.
However, changes in the microstructure at the C-IC
transition are a topic for future study.

0.340

1/3{110}

0.330
0.320
0.310
Martensite, B19

0.300
50

100

150

Commensurate

200

250

Temperature / K

Incommensurate

300

350

Fig. 2 Temperature dependence of (0 ζζ) position in
Ti48.2Ni41.8Cu10.0 alloy.

References[1] Y. Kimura, X. Xu, K. Niitsu, T. Omori, and R. Kainuma, Mater.
Trans. 57, 269 (2016).
[2] K. Niitsu, H. Date, and R. Kainuma, Scr. Mater. 186, 263 (2020).
[3] E. E. Timofeeva, T.Y. Panchenko, A. I. Tagiltsev, N. G.
Larchenkova, A. B. Tokhmetova, Y. I. Chumlyakov, and M. N.
Volochaev, Mater. Lett. 282, 128677 (2021).
[4] M. S. Choi, T. Yamamoto, T. Fukuda, and T. Kakeshita, Philos.
Mag. 88, 2449 (2008).

Yuta Kimura (Corresponding Author, Cooperative Research and Development Center for Advanced Materials)
E-mail: yuta.kimura.b6@tohoku.ac.jp
Naoya Masahashi (Head of Cooperative Research and Development Center for Advanced Materials)
E-mail: naoya.masahashi.e6@tohoku.ac.jp
URL: http://www.crdam.imr.tohoku.ac.jp/en/index-en.html

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Research Centers

Development of YBa2Cu3Oy Based Superconducting Wire
Production for Fusion
High Field Laboratory for Superconducting Materials

For a compact fusion system, 2nd Generation-High Temperature Superconductor (2G-HTS) wire wasdeveloped successfully with a formulation based on YBCO material with Y2O3 nanoparticles acting as random
pinning centers, which were specially optimized for a maximum performance at 20-25 T in the temperature
range of 4.2-20 K. The wire consistently demonstrated the expected properties, while the best performing
samples exhibited Je (20K, 20T) > 1000 A/mm2 and Je (4.2K, 20T) > 2000 A/mm2.

The compact fusion system SPARC, which iscurrently under construction by the joint team of
Massachusetts Institute of Technology (MIT) andCommonwealth Fusion Systems (CFS) relies on theavailability of HTS wire with an engineering current
density Je of at least 700 A/mm2 at 20K and 20T. Twoyears ago, even short laboratory samples with suchcharacteristics were difficult to obtain, while theconsistent production of thousands of kilometers ofsuch wire at reasonable cost seemed unrealistic fromthe viewpoint of current science and engineering.
Our team successfully developed a highly
reproducible approach for the fabrication of 2G-HTS
wire with a formulation based on YBCO material, with
Y2O3 nanoparticles acting as random pinning
centers, specially optimized for a maximum
performance at 20-25T in the temperature range of
4.2-20K. In total, over 300 km of HTS wire with atypical piece length of 300-600 m were delivered forthe fusion application. The wire consistently
demonstrated the expected properties, while thebest performing samples exhibited Je (20K, 20T) >1000 A/mm2 and Je (4.2K, 20T) > 2000 A/mm2, asshown in Fig. 1. The consistency of the Ic performancewas confirmed by Ic measurements at different
facilities including the University of Geneva, National
High Magnetic Field Laboratoy (NHMFL), and Tohoku
University, as shown in the inset of Fig. 1, where theLift Factor is Ic under specified conditions normalizedby Ic at 77K and a self field, Ic (B)/ Ic (77K, sf). Very
good agreement of Lift Factors were confirmed at 20
and 4.2 K for B//c, leading to a consistentdemonstration of Ic properties. The detailed angulardependence of Ic could be evaluated at highmagnetic fields up to 20 T and 20 K as shown in Fig
2. This is important for the design of superconducting
magnets for high field compact fusion reactors.
Recently CFS have succeeded in the achievement of
20 T in a toroidal field coil with 2G-HTS wire [2].

Fig. 1 Field dependence of Ic at 20 and 4.2 K measured
by different facilities, University of Geneva (red), Tohoku
University (black) and NHMFL (blue). The inset shows
Lift Factor, Ic (B)/ Ic (77K, sf) [1].

Fig. 2 Angular dependence of Ic at various temperaturesand magnetic fields [1].

References[1] A. Molodyk et al., Scientific Reports 11, 2084 (2021).
[2] https://news.mit.edu/2021/MIT-CFS-major-advance-towardfusion-energy-0908 (2021).

Valery Petrykin (Corresponding Author, SuperOx Japan LLC)
E-mail: valery.petrykin@superox.co.jp
Hiroyuki Nojiri (Head of High Field Laboratory for Superconducting Materials)
E-mail: hiroyuki.nojiri.e8@tohoku.ac.jp
URL: http://www.hflsm.imr.tohoku.ac.jp/cgi-bin/index-e.cgi

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IMR KINKEN Research Highlights 2022

Creation of New Industrial Materials
Trans-Regional Corporation Center for Industrial Materials ResearchThe Institute for Materials Research (IMR) has launched the Trans-Regional Corporation Center, acomprehensive Institute-wide effort that pairs the research groups at IMR across the innovation spectrum tosolve industrial challenges of the present and address global energy problems for the future. The Center was
established in 2016 based on an agreement between the IMR, Osaka Prefecture Government, and enterprises
sponsored by the government, taking over Osaka and Kansai Center projects.
The Trans-Regional Corporation Center was
established in Osaka as a special unit of the Institute forMaterials Research (IMR), Tohoku University, in April
2016 based on an agreement with the Osaka Prefecture
Government. The Center is sponsored by the Ministry of
Education, Culture, Sports, Science, and Technology,
and takes over the Kansai Center, which carried out its
functions from 2012 to 2016. The Center has three goals.
The first is to address the technical problems thatindustries have struggled to resolve. Secondly, the Center
introduces academic output to industry, with the aim ofapplying these outputs to issues faced by society. Third,
the Center helps to educate the next generation ofmaterials scientists and researchers. We have organizeda bimonthly forum called “Monodukuri Kisokoza”, which
focuses on special topics regarding materials andprocessing. Projects are conducted through broadcollaborations between the government, universities,
research institutions, and other organizations. The Centerhas four venues in the Kansai and Tohoku area, namely,
the Osaka office at the Osaka Prefecture University, theHyogo office at the University of Hyogo, the Sendai officeat the IMR, and the Monozukuri Business Information
Center Osaka at the Creation Core Higashi-Osaka.
The Center has developed various materials andprocesses under collaboration with industry, university
and government organizations. One of these is tofabricate Cu-Ni-Al alloys for Voice Coil Motor (VCM)
systems in smartphone cameras, as shown in Fig. 1.
These have been developed by IMR and DOWAMETALTECH CO., LTD [1]. The alloys are fabricated by aunique thermo-mechanical processing comminating
severe cold-deformation and age heat-treatment, which
promotes precipitation of fine-dispersed γ’-Ni3Al particles
in the matrix phase of γ-Cu, as shown in Fig. 2 [2].
Ordering of the γ’-Ni3Al intermetallic phase can becontrolled by final aging at a low temperature. As a result,
the Cu-Ni-Al alloy plates yields excellent mechanicalproperties, with an ultimate tensile strength of more than
1,400 MPa and a Vickers hardness of 430 Hv. In addition,

Fig. 1 Structure of VCM module and shape of leaf spring [1].

Fig. 2 Transmission electron microscopy-dark field image,
together with the corresponding selected area electron
diffraction pattern (inset), taken from the parent grainsof Cu-Ni-Al alloy specimens developed in our study [2].

the Cu-Ni-Al alloys exhibit favorable features for VCM
systems such as good stiffness, springiness, corrosionresistance, and discoloration-resistance.
Similar collaborative research for practicalapplications utilizing academic knowledge and industrial
technology are in progress. The Trans-Regional
Corporation Center will make efforts to innovate in metallic
material industry through alliances with partners and topromote scientific research in materials science.
References[1] T. Shuto, S. Kasatani, H. Hyodo, H. Watanebe, H. Narieda, A.
Sugawara, and S. Semboshi, Materia Jpn. 60, 119 (2021).
[2] S. Semboshi, R. Hariki, T. Shuto, H. Hyodo, Y. Kaneno, and N.
Masahashi, Metall. Mat. Trans. A, 52, 4934 (2021).

Satoshi Semboshi (Corresponding Author, Trans-Reginal Corporation Center for Industrial Materials Research)
E-mail: satoshi.semboshi.c8@ tohoku.ac.jp
Naoya Masahashi (Head of Trans-Reginal Corporation Center for Industrial Materials Research)
E-mail: naoya.masahashi.e6@ tohoku.ac.jp
URL: http://www.imr.tohoku.ac.jp/en/about/divisions-and-centers/facilities/04.html

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Research Centers

Investigation of the Excited States and Intramolecular ChargeTransfer Transitions in Porphyrin-Based Nanostructures
Collaborative Research Center on Energy Materials

P

orphyrins have attracted research interest for many years due to their relevance in biology, catalysis and medicine.
The application of functional dyes relies on their optoelectronic properties, and the accurate prediction of excited statesin such systems is important for design of new synthetic porphyrins with desirable optical properties. Our study provided
a significant improvement in accuracy of the agreement between theoretical prediction and experiment of the localized
π−π* and intramolecular charge transfer (ICT) transitions, thus allowing confident interpretation of UV− vis−NIR spectra.
For fully conjugated oligoporphyrins (see Fig.
1a), a systematic red-shift in the near-infraredabsorption has been demonstrated which canpotentially be used in photodynamic therapy (PDT)
against cancer. These oligomers have three optical
windows: the lowest energy near-infrared or infraredtransition region (I), the low energy visible range
transition region (II) and the transition region (III)located on the edge of the ultraviolet zone. Therefore,
the accurate assignment and theoretical predictionof the major optical transitions is important in order to
identify the features of these absorption bands formolecular electronics and biomedical applications.
Recently, it was shown that for a large variety ofphthalocyanines and their analogues, the timedependent density functional theory (TDDFT)predicted energies of the Qx- and Qy-bands and their
splitting correlate well with the amount of Hartree−
Fock exchange present in the specific exchangecorrelation functional (ECF), with the LC-BP86 and
LC-wPBE ECFs providing the best agreement
between theory and experiment (<0.05 eV). The pureGGA (BP86) exchange-correlation functional
severely underestimated, while long-range corrected
LC-BP86 and LC-wPBE ECFs strongly overestimated,
the intramolecular charge-transfer (ICT) transitions
experimentally observed in the 450−650 nm region
for the -OR, -SR, and -NR2 substituted phthalocyanines
and their analogues. Hybrid CAM-B3LYP/PCM,
PBE1PBE/PCM, and B3LYP/PCM ECFs were foundto be much better in predicting the energies of such
ICT transitions. Moreover, a single exchangecorrelation functional was not found that could
accurately predict the energies and the splitting of
the Qx- and Qy-bands as well as the energies of ICTtransitions [1].
Based on previous results, our current
investigation showed a good agreement between
theory and experiment with respect to the transition

Fig. 1 (a) Structure porphyrin tapes (n=1-10); (b) experimental
and TDDFT-predicted UV-vis spectrum of tetramer.

energies and intensities (Fig. 1b).
This afforded band assignments which are morereliable than anything reported previously. It was
confirmed that with increasing size of the porphyrintape, there was an increase in ICT states between
spectral regions II and I. Moreover, the spectral
region III was dominated by a single transition statethat originated almost exclusively from a HOMO to
LUMO excitation. A quantitative correlation wasshown between the x-polarized Soret-type transition
and the most intense band that was experimentallyobserved in region II [2]. We also demonstrated, atleast for the shorter tapes (2-4), that spectral region I
was dominated by the y-polarized Soret-typetransition, as shown in Fig. 1b. In the cases ofporphyrins 1-12, our calculations agreed well with thesemi-empirical ZINDO/S spectral predictions andavailable experimental MCD data reported previously.
In
particular
TDDFT-based
sum-over-states
calculations correctly predicted the signs of the MCD
A- and B-terms in the Q-band region.
References[1] R. V. Belosludov, D. Nevonen, H. Rhoda, J. Sabin, and V. N.
Nemykin, J. Phys. Chem. A 123, 132 (2019).
[2] R. V. Belosludov, D. Nevonen and V. N. Nemykin, J. Phys.
Chem. A, 125, 2480 (2021).

Rodion Belosludov (Corresponding Author, Collaborative Research Center on Energy Materials)
E-mail: rodion@tohoku.ac.jp
Tetsu Ichitsubo (Head of Collaborative Research Center on Energy Materials)
E-mail: tichi@tohoku.ac.jp
URL: http://www.imr.tohoku.ac.jp/en/about/divisions-and-centers/facilities/05.html

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IMR KINKEN Research Highlights 2022

Magnetic Materials Design with Theoretical Analysis Tools for Magnetic
and Electronic Structures
Center for Computational Materials ScienceMagnetic materials with complex magnetic structures exhibit various physical phenomena, such as the anomalous Hall effect and themagnetoelectric effect. The occurrence of physical phenomena is dominated by the order parameters, symmetry of magnetic states, andtopology of electronic structures. We developed a new framework to predict physical phenomena in magnetic materials by suggesting new
theoretical tools for analyzing magnetic and electronic structures.
The diversity of the physical properties of magnets provides
a fascinating area of research in condensed matter physics.
Transport phenomena in antiferromagnets have essential
advantages in comparison with ferromagnets because there isno unexpected coupling at the interface and no perturbing strayfield in the devices. There are many restrictions imposed bymagnetic structures on the physical properties of magnets.
Representing a magnetic structure using symmetry, orderparameters, and topology is therefore useful for identifying
possible transport phenomena in magnetic states anddiscovering functional magnetic materials. For example, it is
known that the occurrence of response phenomena, such as theanomalous Hall effect, anomalous Nernst effect, andmagnetoelectric effect, is dominated by the magnetic point
group, which characterizes the macroscopic symmetry of themagnetic structure.
The major challenge in first-principles calculations formagnetic materials is the prediction of the experimental magnetic
structure for a given material. We recently established a theory to
generate possible high-symmetry magnetic structures for given
crystal systems [1] and developed a framework to predict stable
magnetic structures using magnetic-structure generation theory
combined with first-principles calculations [2] (see Fig. 1). We
benchmarked the predictive power of the new framework on the
supercomputing system, MASAMUNE-IMR, at the Center for
Computational Materials Science in IMR, and showed the highaccuracy of the framework for reproducing experimental
magnetic structures [2].
The mechanisms to enhance the anomalous Hall effect,
anomalous Nernst effect, and spin Hall effect in magnetic
materials were also investigated based on electronic structure
analysis of magnetic materials. We investigated in detail thecontribution of the Berry curvature around the topologicaldegeneracy to transport phenomena in hole-doped shandite
compounds Co3InxSn2-xS2 [3], which are representative magnetic
Weyl semimetals, and in orthorhombic CuMnAs [4] (Fig. 2), which
is proposed as an antiferromagnetic semimetal hosting nodal
lines and Dirac points. With these analyses, we predicted a large
anomalous Nernst effect in Co3InxSn2-xS2 and a large spin Hall
effect in orthorhombic CuMnAs caused by specific topologicalFig.1 A schematic view of magnetic structure prediction bycluster multipole method combined with the first-principles
calculations based on spin-density functional theory.

Fig.2 Berry curvature analysis for a magnetic ordered state of
CuMnAs, showing magnetic structure, spin-Berry curvature
originated from the gapped nodal line, and the spin-Hall
conductivity under the magnetic fields along different directions.

degeneracies of the electronic structure around the Fermi
surfaces. The large transport phenomena with a dominant
contribution from topological bands paves the way for the
discovery of new functional magnetic materials in the field of
spintronics.
References[1] M.-T. Suzuki, T. Nomoto, R. Arita, Y. Yanagi, S. Hayami, and H. Kusunose,
Phys. Rev. B 99, 174407 (2019).
[2] M.-T. Huebsch, T. Nomoto, M.-T. Suzuki, and R. Arita, Phys. Rev. X 11, 011031(2021).
[3] Y. Yanagi, J. Ikeda, K. Fujiwara, K. Nomura, A. Tsukazaki, and M.-T. Suzuki,
Phys. Rev. B 103, 205112 (2021).
[4] V. T. N. Huyen, Y. Yanagi, and M.-T. Suzuki, Phys. Rev. B 104, 035110 (2021).

Michi-To Suzuki (Corresponding Author, Center for Computational Materials Science)
E-mail: mts@tohoku.ac.jp
Momoji Kubo (Head of Center for Computational Materials Science)
E-mail: momoji@tohoku.ac.jp
URL: http://www.sc.imr.tohoku.ac.jp/eng/

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Research Centers

Current Status of Collaborative Research Programs of CNSAM
Center of Neutron Science for Advanced Materials

T

he Center of Neutron Science for Advanced Materials is a neutron facility with a background in novel materials
science in IMR. This center manages four neutron instruments at the research reactor facility JRR-3 and thespallation neutron source J-PARC MLF. Here, we report the current status of the research program and theoutcomes obtained from the JRR-3, which has recently started reoperation.
The Center of Neutron Science for Advanced
Materials (CNSAM) was established in 2010 topromote novel material science research using
neutrons. CNSAM operates one diffractometer(HERMES) and two neutron spectrometers (TOPAN
and AKANE) in the JRR-3 research reactor of theJapan Atomic Energy Agency. HERMES can
precisely determine the arrangement of atoms andspins, while their motions are examined by AKANE
and TOPAN. These are used for the target energy
and momentum transfer regimes. POLANO, locatedat the Materials and Life Science Experimental
Facility (MLF) at the Japan Proton Accelerator
Research Complex (J-PARC), is a new spectrometer
designed to perform polarization analysis in higherenergy regions beyond those measured byconventional triple-axis spectrometers. POLANO
and TOPAN are equipped with polarized options
and can disentangle the nuclear and magnetic
contributions. We aim to contribute to condensed
matter physics and materials science with themultipurpose neutron instruments of PATH, which isa collective term for the neutron instruments
managed by the CNSAM.
To achieve this purpose, we established aninternational collaborative research program in IMRfrom FY 2019. We provide opportunities not only forexperiments with neutron beams but also for thedevelopment of neutron devices and analysis
methods, and even for theoretical work using ourneutron data. Proposals can be submitted under
several categories, such as “Neutron experiment at
MLF/JRR-3,”“Instrumental
development,”“Development in analysis method,” “Structural
analysis and data handling,” and “Others”. Under
the category “Others,” proposals on thecomplementary use of neutron and other quantum
beams, such as X-ray and muon beams, areaccepted. In FY 2021, we received 20 and three
proposals from domestic and overseas researchers,
respectively. Furthermore, the research reactor
JRR-3 started reoperation in February 2021, and we
received 29 proposals for our neutron instrument at

Fig. 1 Powder diffraction patterns of as-sintered andreduction annealed Pr2CuO4.

JRR-3 through the user program managed by theInstitute for Solid State Physics, the University ofTokyo.
Figure 1 shows the neutron diffraction profilesof Pr2CuO4, the parent compound of a hightransition-temperature superconductor, which was
obtained at HERMES. The structural changes due
to reduction annealing were clarified using Rietveld
analysis. Combined with the results of structuralrefinement for superconducting La1.8Eu0.2CuO4, wereported the annealing effects on the crystal
structure of R2CuO4 (R: rare earth atom) and its
relationship with the appearance of superconductivity[1]. This is the first publication from JRR-3 since itbegan reoperation.
References[1] M. Fujita, T. Taniguchi, T. Wang, S. Torii, T. Kamiyama, K.
Ohashi, T. Kawamata, T. Takamatsu, T. Adachi, M. Kato, and Y.
Koike, J. Phys. Soc. Jpn. 90, 105002 (2021).

Masaki Fujita (Head of Center of Neutron Science for Advanced Materials)
E-mail: masaki.fujita.b5@tohoku.ac.jp
URL: http://nc-imr.imr.tohoku.ac.jp/index-e.html

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IMR KINKEN Research Highlights 2022

Spin Dynamics Studied by Inelastic Neutron Scattering
Experiments in Spin-Triplet Superconductor UTe2
International Collaboration Center

Superconductivity in UTe has attracted significant attention. The large upper critical field and multiple
2

superconducting phases support a scenario for the spin-triplet state. In contrast to ferromagnetic
superconductors with a spin-triplet state, ferromagnetic fluctuations were not experimentally detected in UTe2.
We investigated the spin dynamics through inelastic neutron scattering experiments and detected
antiferromagnetic fluctuations with an incommensurate wave vector.

Recently discovered superconductivity in UTe2
is a current research topic in condensed matterphysics. It is believed that UTe2 is located in theproximity of the ferromagnetic order; thus, spintriplet superconductivity is expected. In fact, theobserved large upper critical field Hc2, which greatly
exceeds the Pauli paramagnetic limit, supports aspin-triplet scenario. Superconductivity in the spintriplet state is already known in ferromagnetic
superconductors, namely UGe2, URhGe, andUCoGe, which are categorized as weak ferromagnets
with a 5f-itinerant nature. Superconductivity coexists
microscopically with ferromagnetism. Therefore,
ferromagnetic fluctuations are expected to be themechanism of superconducting Cooper pairs;
indeed, ferromagnetic fluctuations have been
experimentally detected. On the other hand, UTe2 isa heavy fermion paramagnet; thus, the ferromagnetic
fluctuations are not trivial, although they are inferredfrom the μSR experiments.
To clarify the magnetic fluctuations, we
performed inelastic neutron scattering experiments
at ILL using a large single crystal of high-quality
UTe2 [1]. As shown in Fig.1(c), antiferromagnetic
fluctuations with an incommensurate wave vector
k1=(0, 0.57, 0) were detected. These fluctuations
saturate below T*~ 15 K, implying a possible
relationship with the NMR results, thermal expansion[2], and resistivity measurements. A quasi-elastic
signal was detected, indicating that the magnetic
moment was parallel to the a-axis with sine-wave
modulations with k1. These low-dimensional
fluctuations are probably due to the unique crystal
formation with a ladder structure as shown in Fig.1(a).
The ferromagnetic fluctuations were notdetected within energy transfers from 0.6 to 7.5 meVdown to 2 K. These results constitute constraints formodels of magnetically mediated superconductivity
in UTe2.

Fig.1 (a)body-centered orthorhombic structure and (b) its Brillouinzone of UTe2. (c) (0,Qk,0) scan of UTe2 at 2.1K above Tc.

At temperatures below Tc~1.7K, a modificationof the excitation spectrum at k1 was observed,
indicating the feedback of superconductivity on themagnetic excitation [3].
This work was done in the framework ofinternational collaboration project of ICC-IMR with
CEA-Grenoble and LNCMI.
References[1] W. Knafo, G. Knebel, P. Steffens, K. Kaneko, A. Rosuel, J.-P.
Brison, J. Flouquet, D. Aoki, G. Lapertot, and S. Raymond,Phys. Rev. B 104, L100409 (2021).
[2] K. Willa, F. Hardy, D. Aoki, D. Li, P. Wiecki, G. Lapertot, and C.
Meingast, Phys. Rev. B 104, 205107 (2021).
[3] S. Raymond, W. Knafo, G. Knebel, K. Kaneko, J.-P. Brison, J.
Flouquet, D. Aoki, and G. Lapertot, J. Phys. Soc. Jpn. 90,
113706 (2021).

Dai Aoki (Corresponding Author, Actinide Materials Science Research Laboratory)
E-mail: dai.aoki.c2@tohoku.ac.jp
Hiroyuki Nojiri (Head of International Collaboration Center)
E-mail: icc-imr@grp.tohoku.ac.jp
URL: http://www.icc-imr.imr.tohoku.ac.jp/

IMR KINKEN Research Highlights 2022

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Research Centers

Local Structure of Sn in β-Ga2O3

Center for Advanced Light Source and Materials ScienceS

n-doped β -Ga2O3 single crystals were grown by the floating-zone method. We successfully investigated the
local structural features of Sn in β -Ga2O3 by X-ray absorption fine structure (XAFS) analysis. The XAFS analysis
indicated the preference of Sn4+ at the octahedral sites in the β -Ga2O3 structure.

β -Ga2O3 has recently attracted attention as an
excellent candidate for transparent conductiveoxides because of its high transmittance of morethan 80% in the wavelength range of 300–1000 nm.
The electrical and optical properties of the β -Ga2O3
could be controlled by introducing the appropriate
dopants. In this context, the interesting properties ofSn-doped β -Ga2O3 have been studied; however,the structural analysis, including the determinationof the valence and environmental structure of the
doped elements, has not been revealed. The crystal
structure of β -Ga2O3 is monoclinic with a spacegroup of C2/m and consists of two crystallographicallydistinct Ga sites denoted as Ga1 and Ga2, with fourand six-fold coordination environments, respectively.
X-ray absorption fine structure (XAFS) analysis withab initio multiple-scattering calculations using the
FEFF code is among the most effective methods for
elucidating the environmental structure of traceelements. Herein, we conducted an advanced
analysis and characterization of Sn-doped β -Ga2O3[1].
Single crystals of Sn-doped β -Ga2O3 weregrown by the floating-zone (FZ) method using adouble ellipsoid mirror furnace. The crystalline
phase of the grown crystals was confirmed using
single crystal X-ray diffraction. The amounts of Sn
were determined using inductively coupled plasma
mass spectrometry (ICP-MS). XAFS spectra at the
Sn K-absorption edges were recorded at the Photon
Factory (Institute of Material Structure Science, HighEnergy Accelerator Research Organization (KEK),
Tsukuba, Japan). Transparent and crack-free Sndoped β-Ga2O3 single crystals were successfullygrown, as shown in Fig. 1. The Sn-doped samples
were bluish in color. The concentration in the Sndoped sample was below the detection limit ofelectron probe micro analysis (EPMA), and the ICPMS results showed a value of 570 ppm.
The K-absorption edge energy of Sn in the Sndoped β -Ga2O3 was identical to that of Sn in SnO2,
suggesting that the Sn atoms are in the tetravalentstate. The Sn doping increased the vacancies of theGa sites and changed the optical properties. To

Fig. 1 Photograph of Sn doped β -Ga2O3 crystals grown
by FZ method.

Fig. 2 Experimental and simulated profiles of Sn K-edge
k3 -weighted χ(k) functions.

directly determine the site preference for Sn,
multiple-scattering EXAFS simulations wereconducted. Figure 2 shows the EXAFS spectra, andthe two models of the Sn environmental structure,
where Sn is present in either Ga1 or Ga2 sites. The
oscillation profile analysis, as shown in Fig. 2,
suggests that the oscillation peak position andintensity of the Ga2 model, in which Sn occupied
the octahedral site, are in good agreement with theexperimental signal. Similar structural analysis was
also performed for Mn-doped β -Ga2O3. Mn K-edge
XAFS spectra analysis revealed an overall
preference of Mn2+ at tetrahedral sites.
References[1] H. Arima-Osonoi, K. Yamazaki, R. Simura, T. Sugawara, K.
Yubuta, K. Sugiyama, and A. Yoshiasa, J. Cryst. Growth 570,
126223 (2021).

Kazumasa Sugiyama (Head of Center for Advanced Light Source and Materials Science)
E-mail: kazumasa.sugiyama.e6@tohoku.ac.jp
URL: http://www.imr.tohoku.ac.jp/en/about/divisions-and-centers/collaboration/08.html

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IMR KINKEN Research Highlights 2022

IMR KINKEN Research Highlights 2022

Demonstration of BCS-BEC Crossover in a Two-Dimensional
Superconductor with Diluted Carrier Density
Laboratory of Low Temperature Materials ScienceB

ardeen-Cooper-Schrieffer (BCS) condensation and Bose-Einstein condensation (BEC) are the two limitingcases describing the superfluid states of paired fermions. Recently, we have succeeded in inducing the crossover
between them in a two-dimensional superconductor, LixZrNCl. It has been demonstrated that a pseudogap phaseappears far above the superconducting transition temperature, which reaches 12% of the Fermi temperature.
(a)(b)
Electrolyte

Gate electrodeClO4VG

ZrNCl
Li +

Open
Covered
10 µm(c)

VDS Tunneling Electrodes

0.4

T*

0.3
T / TFThe condensation of paired fermions is afundamental phenomenon observed in various
systems, such as neutron stars, ultracold atomic
gases, and superconductors. There are two limitingcases for the phenomenon in terms of the couplingstrength (Fig. 1(a)). Bardeen-Cooper-Schrieffer (BCS)
condensation is the weak-coupling or high-density
limiting case in which the pairing and superfluidity
occur
almostsimultaneously.
Bose-Einsteincondensation (BEC) is the strong-coupling or lowdensity limiting case in which the fermion pairs thatare formed at a high temperature condense as thesuperfluid bosons at low temperature. The intermediate
state is referred to as the BCS-BEC crossover. It is
intriguing as well as challenging to realize the BCSBEC crossover using superconductors from the BCS
side by controlling the carrier density and the couplingstrength. This is because localization effects andmagnetic ordering of electrons would impede therealization of such an experiment.
Recently, we have overcome this difficulty with alithium-intercalated layered nitride, LixZrNCl, where Li+
supplies conduction electrons. In this system, thesuperconducting transition temperature Tc enhances
for lower electron doping concentrations, which is
crucial for inducing the BCS-BEC crossover [1]. We
performed the simultaneous measurements ofresistivity and tunneling spectra using an ionic-gating
device with a single crystalline ZrNCl (Fig. 1(b)), which
was designed for electrochemical intercalation of Li+
in the extremely low range (0.0038 ≤ x ≤ 0.28) andshowed the maximum Tc = 19 K at x = 0.011 [2]. Fromthese experiments, we obtained the electric phase
diagram as shown in Fig. 1 (c), where T/TF is thetemperature normalized by the Fermi temperature TF
and ∆ /EF is the coupling strength which increases withdecreasing x. Here, ∆ is the superconducting gap
energy at T → 0 K and EF is the Fermi energy. Notablefeatures include a remarkable increase in the gap
opening temperature T* >> Tc , indicating the

0.2
Pseudogap
0.1
0Superconductivity
0

0.1

0.2
∆ / EF

0.3

Tc
TBKT
0.4

Fig. 1 (a) Schematic concept of BCS state (upper) and
BEC state (lower). (b) Ion-gating device designed for Li
electrochemical intercalation. (c) The phase diagram of
the BCS-BEC crossover in Lix ZrNCl [2].

appearance of a pseudogap phase, and Tc/TF
approaching 0.125, which is the theoretical upper limit
for two-dimensional systems. The findings prove theoccurrence of BSC-BEC crossover, indicating that thegate-doped semiconductor provides an ideal platform
for observing such exotic phenomena.
References[1] Y. Nakagawa, Y. Saito, T. Nojima, K. Inumaru, S. Yamanaka, Y.
Kasahara, and Y. Iwasa, Phys. Rev. B 98, 064512 (2018).
[2] Y. Nakagawa, Y. Kasahara, T. Nomoto, R. Arita, T. Nojima, and Y.
Iwasa, Science 372, 190 (2021).

Tsutomu Nojima (Corresponding Author, Laboratory of Low Temperature Materials Science)
E-mail: t.nojima@tohoku.ac.jp
Takahiko Sasaki (Head of Laboratory of Low Temperature Materials Science)
E-mail: takahiko.sasaki.d3@tohoku.ac.jp
URL: http://ltsd.imr.tohoku.ac.jp/index-e.html

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Research Centers

Research Facility for Physics and Chemistry of Radioactive
and Nuclear Materials
Laboratory of Alpha-Ray Emitters

More than 170 species of radioisotopes and nuclear materials are available for study at the Laboratory ofAlpha-Ray Emitters. This laboratory is one of the most important centers worldwide for studying the physicaland chemical properties of radioactive materials such as actinide compounds. Researchers from many leading
universities and institutes all over Japan visit this facility every year to prepare a variety of materials and conduct
chemical and physical experiments.

The Laboratory of Alpha-Ray Emitters provides a
research environment for the study of 170 radionuclides
and elements, especially alpha-ray emitters, such as
actinide. This lab functions as a source for the preparationof pure crystals of actinide compounds, providing themto other universities and to synchrotron particle
accelerators. In the past decade, actinium-225 (Ac-225),
one of the actinides, has been provided as an interuniversity collaboration to other universities and research
centers. The radiation-controlled area of this laboratory
includes three chemical rooms, three physical rooms,
and other facilities that are equipped with local exhaust
ventilation systems, making the handling of various kindsof radioactive material possible. Many spectrometers,
including those for gamma rays and alpha rays, areavailable.
Hydrothermal synthesis in supercritical water has
been widely used to produce nanoparticles of single
and complex metal oxides. The size, shape, and physicalproperties of the nanoparticles were adjusted by adding
bases or acids to the starting solutions. Based on thisknowledge, a modified hydrothermal synthesis is usefulfor the preparation of UO2 with a fluorite-type crystal
structure, which is widely used as a fuel in light-water
nuclear reactors because of its high melting point.
In the present work, a series of syntheses of UO2 insupercritical water using ethanol and other organic
substances as additives were demonstrated, and thepossibility of controlling the particle size and shape wasstudied [1]. In the absence of organic additives,
uranium(IV) was oxidized to uranium(VI) by nitrate ions,and UO3 was formed. In contrast, the oxidation of
uranium(IV) was suppressed in the presence of additives
such as aldehydes, and UO2+x was formed (Fig. 1).
Oxidation reduction of uranium occurred in the presenceof aldehydes, which buffered the nucleation and crystal
growth. As a result, UO2+x crystals grew, whereas ThO2
did not. From these results, a reaction mechanism for theformation of uranium dioxide from uranyl nitrate with theintervention of organic additives such as aldehydes was
proposed, as shown in Fig. 2. Finally, in the presence ofKenji Shirasaki (Head of Laboratory of Alpha-Ray Emitters)
E-mail: kenji.shirasaki.e4@tohoku.ac.jp
URL: http://alpha.imr.tohoku.ac.jp/en.html

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IMR KINKEN Research Highlights 2022

Fig. 1 XRD patterns of prepared UO2+x with variousorganic additives.

Fig. 2 Proposed reaction mechanism for the formation of
UO2 from uranyl nitrate via the intervention of organic
additives such as aldehydes.

propionaldehyde (PA), acetaldehyde (AA), or
cyclohexanecarboxaldehyde (CA), oxygenation to form
UO2+x occurred at 100 ◦ C. By contrast, the addition of anorganic additive did not promote the hydrothermal
reaction of ThO2. In the hydrothermal synthesis of UO2+x,
an oxygenation mechanism accompanied by oxidationreduction played an important role.
References[1] C. Tabata, K. Shirasaki, A. Sunaga, H. Sakai, D. Li, M. Konaka, andT. Yamamura, CrystEngComm 23, 8660 (2021).

IMR KINKEN Research Highlights 2022

Accurate and Precise Chemical Characterizations for
Advanced Materials Using Appropriate Sample
Preparations in Instrumental Analyses
Analytical Research Core for Advanced Materials

T

he Analytical Research Core for Advanced Materials (ARCAM) measures elemental composition data of metal andinorganic materials. Analytical procedures frequently need to be improved to obtain better sensitivity and reliability.
The ARCAM assays major, minor, and traceelements in consigned samples (e.g., Ref. [1]) byusing various instrumental analyses (Table 1) andconventional chemical analyses (i.e., gravimetricand titrimetric methods). This report describes
recent contributions to improving the analyticalprocedures.
Specimen pre-treatment of pure iron andstainless-steel samples for low-content oxygen
analysis (Fig. 1) have been tested [2]. Chemical andelectrochemical polishings were superior to physicalpolishing for obtaining reliable analytical results.
Appropriate eluents for itaconic acid column inion chromatography have been confirmed [3]. Nitricacid/18-crown-6-ether was suitable for monovalentand high-content divalent cation, whereas lowcontent divalent cation required another eluent ofcopper sulfate/iminodiacetic acid.

Fig. 1 Elemental analyzer for oxygen and nitrogen model
ON836 (LECO Corp., United States).
Kawaguchi, H. Tanimura, S. Imashuku, M. Fichtner, and T.
Ichitsubo, Chem. Mater. 33, 6983 (2021).
[2] T. Chiba, Tech. Res. Rep. Tech. Serv. Cent. IMR 29, 33 (2020).

References[3] Y. Kabasawa, Tech. Res. Rep. Tech. Serv. Cent. IMR 29, 41[1] T. Hatakeyama, H. Li, N. L. Okamoto, K. Shimokawa, T.

(2020).

Table 1 Methods for chemical characterization.
Analytical method

Instrument

Inductively coupled plasma atomic emission
spectrometry (ICP-AES) [1]

AROCS FHM22 MV130 (SPECTRO Analytical Instruments GmbH,Germany) and IRIS Advantage DUO (Thermo Jarrell Ash Corp.,
United States)

Inductively coupled plasma mass spectrometry (ICPMS)

iCAP TQ (Thermo Fisher Scientific Inc., United States)

Atomic absorption spectrometry (AAS) [1]

contrAA 800 D (Analytik Jena AG, Germany)

Microwave induced plasma atomic emission
spectrometry (MIP-AES)

4210 MP-AES (Agilent Technologies, Inc., United States)

Gaseous analyses (hydrogen, carbon, nitrogen,oxygen, and sulfur) [2]CS844 (LECO Corp., United States) for carbon and sulfur; ON836(LECO Corp., United States) for nitrogen and oxygen; and EMGA821 (HORIBA, Ltd., Japan) for hydrogen

Spectrophotometry

U-2910 (Hitachi, Ltd., Japan)

Ion chromatography [3]850 Professional IC (Metrohm AG, Switzerland)

Kenichi Nakayama (Corresponding Author, Analytical Research Core for Advanced Materials)
E-mail: ken1naka@tohoku.ac.jp
Toyohiko J. Konno (Head of Analytical Research Core for Advanced Materials)
E-mail: tjkonno@tohoku.ac.jp
URL: http://www.imr.tohoku.ac.jp/en/about/divisions-and-centers/service-divisions/03.html

IMR KINKEN Research Highlights 2022

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International Collaborative Research

IMR KINKEN Research Highlights 2022

Research

International Collaborative Research

Giant Spin Hetero-Spin Complex with S=48

The third largest spin achieved on a single molecule, of S=48, was synthesized as a heterometallic system

coupling Cr and Gd ions with sizable antiferromagnetic interactions. The structure contained two magnetic
cores of Cr5Gd6, in which each Cr ion bridged the neighboring Gd ions. The two units were coupled by two
additional Gd ions, resulting in an S=48 ground state. The dominant antiferromagnetic interaction and anisotropy
were determined by high-field magnetization.

The creation of a giant artificial spin beyond
that of natural elements has been an important
target of molecular-based compounds. For larger
spins, the uncertainty originating from quantum
mechanics is smaller, and thus, quantum mechanicalmanipulation is easier. Moreover, such a giant spin
can be a candidate for molecular-based magnetic
memory with sizable anisotropy.
There have been several recipes for giant spin
synthesis. 3d mixed-valence compounds withferromagnetic
interactions
have
contained
successful examples, such as Fe42 [1]. The use of
rare-earth ions has provided another route forachievement of large molecular moments. Despite
the rare successes of homometallic compounds
associated with weak exchange interactions,heterometallic compounds are more promisingbecause of their larger exchange interactions. The
concept of a heterometallic complex is extended toa radical rare-earth compound, where the radical
spins contribute to the connecting block rather than
to the size of the total spin.
Here, we investigated a Cr10Gd18 cluster
consisting of two magnetic cores of Cr5Gd6, asshown in Fig. 1. In each core, two Gd ions of S=7/2
were coupled to the S=3/2 Cr ion, and then four
CrGd2 units were connected through a Cr ion at thecenter. Strong magnetic coupling between Cr andGd caused the entire molecule to be an S=48 giant
spin cluster.
To examine the magnetic parameters of thesystem, we measured the magnetization at 0.4 K up
to 25 T. The magnetization curve shows two distinct
features, namely the low field saturation at around
95 µB and the increase above 8 T. The former showsthat the Cr and Gd are antiferromagnetically aligned
and form a ferrimagnetic ground state. The lattershows the strength of the antiferromagnetic
interactions. The analysis using classical MonteCalro simulation with a four exchange coupling
parameter model shows that the two types of
exchange couplings between Cr and Gd are
antiferromagnetic and the other two exchange
couplings between Gd ions are ferromagnetic. The
Hiroyuki Nojiri (Magnetism Research Laboratory)
E-mail: hiroyuki.nojiri.e8@tohoku.ac.jp
URL: http://www.hfpm.imr.tohoku.ac.jp

54

IMR KINKEN Research Highlights 2022

Fig. 1 Schematic view of the Cr10Gd18 cluster [2]. Greenand pink balls are Gd and Cr ions, respectively.

Fig. 2 Magnetization curve of Cr10Gd18 cluster at 0.4 K [2].

presence of four different exchange coupling aswell as the anisotropy causes the magnetization
curve to be linear between 8 and 18 T.
It is notable that both Cr and Gd have very
isotropic spins and thus the total spin of S=48
represents the ground state of the system. This is anadvantage of using Gd without orbital moments.
References[1] S. Kang et al., Nat. Commun. 6, 5955 (2015).
[2] L. Qin, H.-L. Shang, Y.-Q. Zhai, H. Nojiri, C. Schröder, and Y.Z. Zheng, iScience 24, 102350 (2021).

IMR KINKEN Research Highlights 2022

Role of Cementite and Retained Austenite in Austenite Reversion
from Martensite and Bainite in Fe-2Mn-1.5Si-0.3C AlloyT

he effect of cementite (θ) and retained austenite (RA) on the morphology and kinetics of reverted austenite (γ) in Fe-MnSi-C alloys and its mechanisms have not been well understood yet. Therefore, the γ reversion behaviors were comparatively
investigated by changing θ and RA distributions in initial microstructures in this study. Pre-tempering or prolonged
austempering coarsened the θ particles, which promoted the formation of globular austenite. Retained austenite inhibitedthe formation of globular austenite, and the acicular austenite was formed by its thickening.
It is possible to improve fuel consumption and electric
power efficiencies as well as the collision safety of automobiles
by developing higher strength steels. One of the candidates is
the transformation-induced plasticity (TRIP) steel, whichcontains a large amount of retained austenite (RA) and yields
high strength; in addition, it has good ductility for absorption ofenergy in a collision. TRIP steels are produced by austenite
reversion treatment followed by austempering. The mechanicalproperties of TRIP steel largely depend on the phase fraction
and stability of the RA formed during austempering, which arestrongly influenced by the composition, size, and morphologyof the reverted austenite (γ). In γ reversion from lath martensite,
two typical morphologies, namely, fine acicular and coarse
globular, which have different crystal structures and alloying
element partitioning were widely observed [1-4]. It was reported
that cementite (θ) particles and pre-existed RA play crucial
roles in the γ reversion from martensite. θ precipitates during theheating of the as-quenched martensite, which can act as anucleation site for globular γ [4]. Meanwhile, RA enhances the γmemory effect by promoting the formation of acicular γ in thereversion process from martensite.
Therefore, the effects of θ and RA on the kinetics andmicrostructure evolution in austenite reversion of an Fe-2Mn1.5Si-0.3C (mass%) alloy have been studied by investigating
the γ reversion from as-quenched martensite, tempered
martensite, and bainite [5].
As shown in Fig. 1, pre-tempering or prolonged
austempering coarsened the θ particles, which promoted theformation of globular γ. Theoretical calculation showed that thelarger θ particles with high density increased the nucleation
potency of globular γ. Pre-existed RA suppressed theprecipitation of θ particles, which inhibited the formation of
globular γ, and the acicular γ formed by its thickening.
High-temperature
pre-temperingor
prolonged
austempering retarded the reversion kinetics, while lowtemperature pre-tempering or the presence of RA havenegligible influences on the kinetics. Thermodynamical
calculation suggests that the supression of reversion kinetics by
pre-tempering or austempering was not due to its suppression
upon nucleation but due to the growth of reverted γ.

Fig. 1 Schematic illustration of the influences of cementite
particles and pre-existed retained austenite on reversion
behavior of globular and acicular austenite.

The present results demonstrate that the kinetics andstructure of γ reversion can be controlled by changing the
microstructure before the reversion treatment, without changing
the alloying element or reversion treatment condition. Further,
the results guide the design for optimizing the microstructure of
the TRIP steels to obtain excellent properties.
References[1] S. Matsuda and Y. Okamura, Tetsu-to-Hagané 60, 226 (1974).
[2] M. R. Plichata and H. I. Aaronson, Metall. Trans. 5, 2611 (1974).
[3] X. Zhang, G. Miyamoto, Y. Toji, S. Nambu, T. Koseki, and T. Furuhara, Acta
Mater. 144, 601 (2018).
[4] X. Zhang, G. Miyamoto, T. Kaneshita, Y. Yoshida, Y. Toji, and T. Furuhara.
Acta Mater. 154, 1 (2018).
[5] X. Zhang, G. Miyamoto, Y. Toji, Y. Zhang, and T. Furuhara, Acta Mater., 209,
116772 (2021).

Goro Miyamoto (Corresponding Author, Microstructure Design of Structural Metallic Materials Research Laboratory)
E-mail: goro.miyamoto.e8@tohoku.ac.jp
Tadashi Furuhara (Microstructure Design of Structural Metallic Materials Research Laboratory)
E-mail: tadashi.furuhara.c3@tohoku.ac.jp
URL: http://www.st-mat.imr.tohoku.ac.jp/en/index.html

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International Collaborative Research

Development of a Novel Pyrosilicate Scintillator and an
Investigation of its Thermal Quenching MechanismIn order to develop a novel rare-earth (RE) pyrosilicate scintillator, we focused on a complex RE pyrosilicate
and grew a Ce-doped (La,Y)2Si2O7 single crystal by the micro-pulling-down method. We succeeded in growing
a transparent crystal and found that the thermal quenching of Ce3+ emission is caused by a combination ofthermally activated ionization and thermally activated crossover.
Scintillation crystals convert energy of ionizing
radiation to ultra-violet or visible light, and are widely usedin radiation detector applications such as oil well logging,medical imaging and high energy physics. We havefocused on Ce-doped RE2Si2O7 as promising oxide
scintillators, which have excellent scintillation properties
but are difficult to grow into single crystals from the melt
because of the incongruent melting composition of most
RE2Si2O7. In order to develop RE2Si2O7 single crystals, we
designed materials based on Pauling’s electrostatic
valence rule and demonstrated that a partial substitution of
Gd with La in Gd2Si2O7 crystals (Ce:La-GPS) transforms
the originally incongruent melting compound to acongruently melting one without any remarkable negative
effects [1,2]. In the development of other RE2Si2O7
scintillators, we focused on (La0.6Y0.4)2Si2O7 and tried to
grow a single crystal [3].
(Ce0.015La0.600Y0.385)2Si2O7 (Ce:La-YPS) crystal wasgrown by the micro-pulling-down method and is shown in
Fig. 1. The grown crystal was 3.5 mm in diameter and 25
mm in length. In the initially grown section of the crystal(i.e., on the left-hand side of Fig. 1), many micro-cracks
were present because of the difference in the lattice
constants between the seed crystal and the grown crystal.
However, we succeeded in growing a transparent crystal in
the central section. The final section of the crystal, as seenon the right-hand side of Fig. 1, was opaque. When thechemical composition of the opaque part in the final section
was evaluated, a Si-rich phase and a pyrosilicate phasewere detected.
For the evaluation of the thermal quenching

Fig. 1 Grown crystal by micropulling-down methodmechanism of Ce:La-YPS, the photoluminescence (PL)decay curves under an excitation by a 339 nm nanosecond
LED were measured at different temperatures. These
results were fitted with a single-barrier model, and theactivation energy of the thermal quenching and thequenching temperature (T50%) were determined to be 0.62
eV and 526 K, respectively. The T50% of Ce:La-YPS isrelatively high compared to other Ce-doped crystals suchas Lu2SiO5 [4].
The temperature dependence of the background
intensity of the PL decay curve is shown in Fig. 2 (a), whichindicates that the background intensity increases with anincreasing temperature starting from approximately 400 K.
This increase is most likely caused by the escape of theelectrons from the Ce3+ 5d1 state into the conduction band,
resulting in delayed radiative recombination. Therefore, it isthought that a thermal ionization is one contributor to thethermal quenching mechanism in Ce:La-YPS. Anothercontributor could be the classical thermal quenching due
to the thermally activated nonradiative crossover from theCe3+ 5d1 excited level to the 4f ground state.
References[1] A. Yoshikawa, S. Kurosawa, Y. Shoji, V. I. Chani, K. Kamada, Y. Yokota,
and Y. Ohashi, Cryst. Growth Des. 15, 1642 (2015).
[2] M. Nikl and A. Yoshikawa, Adv. Opt. Mater. 3, 463 (2015).
[3] T. Horiai, J. Paterek, M. Jarosova, J. Rohlicek, S. Kurosawa, T. Hanada,
M. Yoshino, A. Yamaji, S. Toyoda, H. Sato, Y. Ohashi, K. Kamada, Y.
Yokota, A. Yoshikawa, and M. Nikl, J. Cryst. Growth 573, 126252 (2021).
[4] V. Babin, V. V. Laguta, M. Nikl, J. Pejchal, A. Yoshikawa, and S.
Zazubovich, Opt. Mater. 103, 109832 (2020).

Fig. 2 (a) Temperature dependence of PL decay time and background intensity,(b) schematic view of thermal quenching

Akira Yoshikawa (Advanced Chrystal Engineering Research Laboratory)
E-mail: akira.yoshikawa.d8@tohoku.ac.jp
URL: http://yoshikawa-lab.imr.tohoku.ac.jp/index-e.html

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IMR KINKEN Research Highlights 2022

Anomalous Compliance of Interpenetrating-Phase Composite
of Ti and Mg Synthesized by Liquid Metal Dealloying

Low modulus biomaterials, which can ensure fast healing of hard tissues are potential candidates forbiomedical implants. In this work, a low modulus (17.6 MPa) interpenetrating-phase composite of Ti and Mg,
mimicking the elastic behavior of human bone was synthesized. It has been demonstrated that the origin of the
low modulus of the composite can be related to a weakened interface between the constituents.

Dealloying-based composites demonstrate asignificant deviation of their mechanical behavior
from that estimated using various rules of mixtures[1-2]. For example, nanoporous metal and polymer
composites are substantially stronger and harderthan the individual nanoporous metal or polymer [1].
Moreover, these metal-polymer composites exhibit
extremely low Young’s modulus values comparedwith theoretical predictions [1]. In a recent study, it
was demonstrated that the Young's modulus of thedealloying-based composite, which contains both
Fe and Mg is significantly lower than that of eachconstituent [2]. This anomalous behavior isassociated with interfacial phenomena.
In nanoscale materials, interfaces and interfacial
areas play a crucial role in determining the effective
mechanical properties of materials. It is possible toaccount for a significant reduction of Young's
modulus compared to perfect cohesion in inclusioncomposites, which have large interface-to-volume
ratios; this is achieved by using interface elasticity
theory modeling. The magnitude of the effectdepends on the structure morphology and thecharacteristic length scale; that is, with increasing
structure size, the interfacial influence on theeffective modulus decreases.
The characteristic length scale in the recent
dealloying-based interpenetrating-phase Ti-Mg
composite that possesses an anomalously low

effective elastic modulus is in the micron-scale
regime [3], which is several orders of magnitude
higher compared to the abovementioned
nanomaterials; this indicates a different origin of alow modulus value. The composite of Ti and Mg(synthesized by liquid metal dealloying) features ananomalously low Young's modulus of 17.6 ± 0.5 GPa(several times lower than that of each constituent)and moderate yield strength of 180 ± 10 MPa [3].
The origin of the anomalously low modulus isassociated with the weak interface between
constituent Ti and Mg phases, as confirmed using
micromechanical modeling. The result suggeststhat even moderate porosity in the Ti-Mg composite
affects the overall behavior drastically if localized,
e.g., homogeneously distributed at the interface.
This localized porosity is likely due to the shrinkageof the Mg phase upon solidification and unequal
shrinkage of the Ti and Mg phases upon cooling,caused by unequal coefficients of volumetric
thermal expansion.
References[1] A.V. Okulov, A.S. Volegov, J. Weissmüller, J. Markmann, and
I.V. Okulov, Scripta Mater. 146, 290294 (2018).
[2] I.V. Okulov, P.-A. Geslin, I.V. Soldatov, H. Ovri, S.-H. Joo, and
H. Kato, Scripta Mater. 163, 133136 (2019).
[3] I.V. Okulov J. Wilmers, S.-H. Joo, S. Bargmann, H. S. Kim, and
H. Kato, Scripta Mater. 194, 113660 (2021).

Ilya Okulov (Corresponding Author, Leibniz-Institut für Werkstofforientierte Technologien – IWT Bremen)
E-mail: i.okulov@iwt.uni-bremen.de
Hidemi Kato (Non-Equilibrium Materials Research Laboratory)
E-mail: hidemi.kato.b7@tohoku.ac.jp
URL: http://www.nem2.imr.tohoku.ac.jp/index-e.html

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International Collaborative Research

Evaluation of Edge Domains in Giant Magnetoresistive Junctions

In nanoelectronic devices, miniaturization increases the total length of the current paths and the associated
Joule heating. Even with optimization of the chip design, waste heat cannot be ignored in the total power
consumption of the device. In this work, we propose a new method to use the waste heat to generate additional
spin-transfer torque in a magnetic insulator to assist current-induced magnetization reversal used in magnetic
random access memory, which meets the policy of sustainable development recently set by the United Nations.
Recent progress in spin caloritronics has revealed
that spin waves can be efficiently induced in a magnetic
insulator [1, 2], which can be used for energy
harvesting. However, the spin-transfer torque inducedby spin waves has not been investigated. In this study[3], we demonstrated spin-wave-assisted magnetization
reversal in a current-perpendicular-to-plane (CPP)
giant magnetoresistive (GMR) nanopillar.
A GMR multilayer, consisting of Co2Fe0.4Mn0.6Si(CFMS) (5)/Ag0.78Mg0.22 (5)/CFMS (5), was grown on a
Cr (20)/Ag (40) seed layer on a MgO(001) substrate by
ultrahigh vacuum magnetron sputtering (all thicknesses
are given in nanometers). The Heusler-alloy CPP-GMR
junction was then patterned into elongated nanopillars
with long axes between 100 and 800 nm using photoand electron-beam lithography, as well as Ar-ion
milling. These nanopillars were encapsulated by a
5-nm-thick magnetic insulator of Fe2O3 with a Cr (1)/
AlO (2) layer to enhance adhesion, followed by the top
electrode of Ag (2)/Au (5). The magnetic transport
properties were measured using a probe station inboth field- and current-induced modes.
The CPP-GMR junctions were evaluated in astandard manner using an applied external field. With
Fe2O3, an asymmetric GMR curve was obtained with
GMR ratios of (32.8±0.1)% and (10.2±0.1)%. Thisasymmetry was induced by the formation of edge
domains coupled with the spin-wave induced in Fe2O3,
as shown in Fig. 1(a). Without Fe2O3, a symmetric GMR
curve was observed, as shown in Fig. 1(b).
In Fig. 1(c), the corresponding current-induced
magnetization reversal was measured under amagnetic field of -10 Oe, forming an antiparallel
configuration. The switching current density wasestimated to be (8.0±0.7)×107 A/cm2 owing to (i)conventional spin-transfer torque by the pinned layer,and (ii) the influence of the edge domains exchangecoupled with a spin wave in Fe2O3. Here, currentinduced magnetization switching from parallel toantiparallel configurations could not be achieved
because of contribution (ii).

Fig. 1 GMR curves for a pillar (120 and 60 nm in long andshort axes, respectively) (a) with and (b) without Fe2O3
with a sensing current of 100 µA. The corresponding
current-induced magnetisation switching profiles (c)with Fe2O3 under a magnetic field of -10 Oe and (d)without Fe2O3 under a field of 3 Oe.

Without Fe2O3, the current switching in Fig. 1(d) is
dominated by contribution (i), with switching current
densities of (1.1±0.1)×107 A/cm2 and (2.2±0.2)×107 A/
cm2 for the negative and positive currents, respectively.
These results indicate that the presence of thespin wave in Fe2O3 can assist in magnetization reversal
only when the spin wave is parallel to the free-layer
magnetization. By comparing Figs. 1(c) and (d), theedge domain volume can be estimated to be almost
1/3 of that of the free layer. Further control of the GMR
behavior can be achieved to reduce the power
consumption in magnetization reversal.
References[1] H. Chang, P. A. Praveen Janantha, J. Ding, T. Liu, K. Cline, J. N.
Gelfand, W. Li, M. C. Marconi, and M. Wu, Sci. Adv. 3, e1601614(2017).
[2] P. Jiménez-Cavero, I. Lucas, A. Anadón, R. Ramos, T. Niizeki, M.
H. Aguirre, P. A. Algarabel, K. Uchida, M. R. Ibarra, E. Saitoh, and
L. Morellón, APL Mater. 5, 026103 (2017).
[3] W. Frost, T. Seki, T. Kubota, R. Ramos, E. Saitoh, K. Takanashi,and A. Hirohata, Appl. Phys. Lett. 118, 172405 (2021).

Atsufumi Hirohata (Corresponding Author, University of York)E-mail: atsufumi.hirohata@york.ac.uk
Koki Takanashi and Takeshi Seki (Magnetic Materials Research Laboratory)
E-mail: koki.takanashi.d2@tohoku.ac.jp, takeshi.seki@tohoku.ac.jp
URL: http://magmatelab.imr.tohoku.ac.jp/

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IMR KINKEN Research Highlights 2022

Alloying Effects on Deuterium Retention in Ion-Irradiated Tungsten
International Research Center for Nuclear Materials and ScienceThe alloying effects of molybdenum, tantalum, and rhenium on deuterium retention in ion-irradiated tungsten alloys were investigated.
A significant decrease of irradiation-induced deuterium retention by rhenium doping was observed, but there were almost no effects
in molybdenum and tantalum doping. This was attributed to the interaction between solute and irradiation-induced defects.
Tungsten (W) and its alloys are recognized as leading
candidates for plasma-facing material in a fusion reactor
because of their attractive physical and chemical properties,
such as high melting point, high thermal conductivity, highthreshold energy for sputtering and low solubility of hydrogenisotopes. During service in a fusion reactor, W experiences
irradiation of high-energy neutrons and energetic particles of
deuterium (D) and tritium (T). High-energy neutrons induce
displacement damage in W. Previous neutron-irradiation
experiments have shown that irradiation-induced defects inpure W act as strong traps for hydrogen isotopes, and hence
neutron irradiation should lead to a significant increase in T
inventory in the vacuum vessel of a fusion reactor. Here, weinvestigated the effects of alloying elements such as
molybdenum (Mo), tantalum (Ta), and rhenium (Re) on theretention of hydrogen isotopes in W after irradiation.
The samples were plates of W-2.5%Mo, W-5%Ta, and
W-5%Re alloys (in atomic percent). They were heated in
vacuum at 1273 K for 1 h to relieve strain potentially induced
during fabrication and to remove hydrogen present in thesamples as an impurity. Displacement damages were
induced by irradiation of 6.4 MeV iron (Fe) ions to 0.26 dpa
at 1073 K by using the Dual-Beam Facility for Energy Scienceand Technology at Kyoto University. The depth of thedamaged region was estimated to be ~2 μm using Monte
Carlo simulation. The irradiated samples were exposed to D2
gas at 0.1 MPa at 673 K for 10 h. The D retention was thenmeasured with thermal desorption spectrometry (TDS), as
shown in Fig. 1. The D retention in the non-irradiated W
sample was small but it increased significantly after Fe ion
irradiation due to the trapping effect of irradiation-induced
defects. The irradiated W-5Ta and W-2.5Mo alloys showed D
retention comparable with that of irradiated W [2], while the Dretention in irradiated W-5Re alloy was far smaller [1]. As
previously mentioned, the thickness of the damaged zone
was ~2 μm, while the sample thickness was 500 μm. Boththe damaged zone and the non-irradiated volume therefore
contributed to thermal desorption spectra. Hence, the Dretention in the damaged zone was evaluated as thedifference in D retention between non-irradiated andirradiated samples of the same material, as shown in Fig. 2.
The addition of Re was effective in mitigating the irradiation-

Fig. 1 Desorption spectra of D by TDS measurement. [1,2]Fig. 2 Deuterium retention in W and W alloys.

induced increase in hydrogen isotope retention, while Mo
and Ta showed no significant effects [1, 2]. Theseobservations roughly agreed with the order of binding
energy of a solute atom and W self-interstitial atom reported
by Suzudo et al. in Ref. [3].
References[1] Y. Hatano, K. Ami, V. K. Alimov, S. Kondo, T. Hinoki, T. Toyama, M.
Fukuda, A. Hasegawa, K. Sugiyama, Y. Oya, M. Oyaidzu, and T. Hayashi,
Nucl. Mater. Energy, 9, 93 (2016).
[2] J. Wang, Y. Hatano, T. Hinoki, V. Kh. Alimov, A. V. Spitsyn, N. P. Bobyr, S.
Kondo, T. Toyama, H. T. Lee, Y. Ueda, and T. Schwarz-Selinger, J. Nucl.
Mater., 545, 152749 (2021).
[3] T. Suzudo, T. Tsuru, and A. Hasegawa, J. Nucl. Mater., 505, 15 (2018).

Yuji Hatano (Corresponding Author, University of Toyama)
E-mail: hatano@ctg.u-toyama.ac.jp
Yasuyoshi Nagai (Head of International Research Center for Nuclear Materials and Science)
E-mail: yasuyoshi.nagai.e2@tohoku.ac.jp
URL: http://www.imr-oarai.jp/en/

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International Collaborative Research

Determination of Magnetic, Electronic and Lattice Contributions
to Low-Temperature Specific Heat
Cooperative Research and Development Center for Advanced Materials

T

he separation of magnetic and non-magnetic contributions to the specific heat of ferromagnetic (FM) solids wasapplied to Ni-Mn-In alloys. It is shown that the disregard of magnetic contribution results in a noticeable underestimationof the Debye temperature and overestimation of the specific heat of the electron subsystem of a FM solid.
Experimental and theoretical research has shownthat the low-temperature state of Ni50Mn50-xInx alloys isferromagnetic (FM) austenite if x > 16 andantiferromagnetic (AFM) martensite if x < 15 (see [1,2]and references therein). The specific heat of Ni50Mn50xInx alloys was measured at low temperatures in a wide
composition range [1]. It has been shown that the
specific heat value measured for Ni50Mn50-xInx alloys
with x < 15 was significantly different from that measured
for alloys with x > 16 [1].
The low-temperature specific heat of a magnetic
solid can be expressed by a sum
C(T) = γT + βT 2 + CM (T),(1)where the first summand is the specific heat of theelectronic subsystem, the second summand is a Debye
term describing the specific heat of the crystal lattice
and the third summand describes the specific heat ofmagnetic excitations (magnons) [2]. In the absence ofthe magnetic term, the C(T)/T is a linear function of T2.
In this connection the coefficients β and γ are usually
determined as the slope and intercept of experimental
C(T)/T vs T 2 dependence. The Debye temperature TD isthen estimated from the determined β value.
It was shown very recently that the determinationof β and γ values is impossible if CM (T) is disregarded[2]. This conclusion is explained here for the FM phaseof Ni50Mn50-xInx.
For an FM solid, the specific heat of magnetic
excitations is equal to CM (T) = ΚFMT 3/2, where thetemperature-independent coefficient ΚFM is inversely
proportional to the third power of the Curie temperature(see [2] and references therein). Figure 1 shows
experimental and theoretical determinations of the total
C(T)/T value vs T 2 obtained for the ferromagnetic stateof an Ni50Mn33.8In16.2 alloy (x = 16.2). The magnetic andelectronic contributions to the C(T)/T function are
shown for comparison. It is seen that the magnetic
contribution exceeds all others in the temperature
range from 2 K to 8 K. Due to this, the value γ = 2.3
mJ(mol)-1K-2, determined by the Eq. (1) fit is strongly
different from the value of 5.1 mJ(mol) -1K-2 that results

Fig. 1 The experimental (open circles) and theoretical(lines) dependencies of C(T)/T ratio on the squared
temperature determined for Ni50Mn33.8In16.2 alloy.
Magnetic (red solid line), electronic (pink dashed line)
and lattice contributions (brown dotted line) to this ratio
are shown for comparison.

from the linear extrapolation of experimental
dependence C(T)/T to zero temperature. The differenceis caused by the magnetic contribution to specific heat,
which, in turn, causes the noticeable nonlinearity ofC(T)/T vs T 2.
For the AFM phase of Ni50Mn50-xInx with x < 15,
the magnetic contribution strongly depends on the
Néel temperature TN [2]. This contribution exceeds the
Debye term if TN < 0.3TD. The magnon and latticecontributions to the specific heat are cubic functions of
the temperature, and so the separation of thesecontributions from the specific heat of an AFM solid is
an open problem.
It can be concluded that the magnetic subsystem
noticeably contributes to the low-temperature specificheat and cannot be disregarded.
References[1] R. Y. Umetsu, X. Xu, W. Ito, and R. Kainuma, Metals 7, 414 (2017).
[2] A. Kosogor, V.A. L'vov, R.Y. Umetsu, X. Xu, and R. Kainuma, J.
Magn. Magn. Mater. 541, 168549 (2022).

Anna Kosogor (Corresponding Author, Institute of Magnetism National Academy of Sciences of Ukraine)
E-mail: annakosogor@gmail.com
Naoya Masahashi (Head of Cooperative Research and Development Center for Advanced Materials)
E-mail: naoya.masahashi.e6@tohoku.ac.jp
URL: http://www.crdam.imr.tohoku.ac.jp/en/index-en.html

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Spin Reorientation and Unusual Tetra-Critical Point in MnCr2S4High Field Laboratory for Superconducting MaterialsT

he high magnetic phase diagram of the spinel compound MnCr2S4 was investigated by combining elementspecific magnetization measurements of X-ray magnetic circular dichroism (XMCD) and macroscopic
thermodynamic measurements. The re-orientation of the sublattice magnetic moments was determined by
XMCD and combined with macroscopic results. The present study shows the importance of the combinationof microscopic and macroscopic analyses, which has been enabled by the collaboration of several laboratories.
Spinel compounds exhibit a variety of physicalproperties owing to spin-lattice coupling andcompetition for exchange interactions. MnCr2S4 hasstrong spin frustrations and shows successive
phase transitions from paramagnetic to ferrimagnetic
at 65 K and then to a canting phase at 5 K. Sequential
phase transitions occur at 3.5 T, 11 T, and 23.5 T. To
understandthiscomplicatedmagnetization
process, we used the bridge proposal of GIMRT to
combine measurements in high-field laboratories
and the 40 T soft X-ray magnetic circular dichroism
at SPring8.
Figure 1 shows the XMCD at the L3 edge of Mn[1]. At low temperatures, a few anomalies of the Mn
signal were observed, indicating rearrangement of
the Mn spins. In contrast, the Cr signal decreased
toward 11 T and then increased again. It clearlyshows the complex process of increasing tilt fromthe external magnetic field and then re-aligning
along it. Detailed investigations indicated that thismaterial has a quadruple critical point.
Generally, a quadruple critical point is notexpected in an isotropic spin system with threesites. In this material, ultrasonic anomalies havebeen observed in the phase transition; therefore, theexistence of spin-lattice coupling is considered tobe the key. In such a case, the Monte Carlocalculation shows that the symmetry of Z2 isspontaneously broken and a staggered magnetic
field of two components causes the phase diagram
to have a tetra-critical point owing to the interplay ofthe symmetries of O(3) and O(2) and the recovery ofO(2) symmetry above 23.5 T.
The present result shows the complexity ofspinel compounds as well as the potential tuning of
their magnetic properties by spin-lattice coupling.

Fig. 1 Magnetic field dependence of Mn and Cr L3 edge
XMCD
signalcomparedwithmacroscopic
magnetization curve. After Ref. [1].

References[1] S. Yamamoto, H. Suwa, T. Kihara, T. Nomura, Y. Kotani, T.
Nakamura, Y. Skourski, S. Zherlitsyn, L. Prodan, V. Tsurkan, H.
Nojiri, A. Loidl, and J. Wosnitza, Phys. Rev. B 103, L020408(2021).

Hiroyuki Nojiri (Head of High Field Laboratory for Superconducting Materials)
E-mail: hiroyuki.nojiri.e8@tohoku.ac.jp
URL: http://www.hflsm.imr.tohoku.ac.jp/cgi-bin/index-e.cgi

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International Collaborative Research

Ab Initio Design of Effective Magnetostriction Materials forElectric Power Generation
Center for Computational Materials ScienceAlthough magnetostriction is expected to contribute to electric power generation in SDGs, it is still necessary
to increase the magnetostriction coefficient. We theoretically investigated the efficient doping effect in a Ga-Fe
magnetostriction alloy (galfenol). Transition metal elements were unsuccessful, but La-doped galfenol showeda satisfactory increase in the magnetostriction property.
Materials with large magnetostrictions areextensively used as magnetic field sensors, magnetomechanical actuators, and energy harvesters. A large(and preferably linear) magnetic field response isessential. Here, we proposed a consistent descriptionof the effect of various types of doping with transition
metals (TM) and rare-earth (RE) elements. We explain
why the experimentally measured values of the λ001
coefficients did not change or even decreased in thecase of TM doping, whereas in the RE type of doping,they increased.
The first-principles calculations of the structuraland magnetic properties of the Fe-Ga alloy systems
were performed using the Vienna Ab initio Simulation
Package (VASP) with the supercell approach. A
4×4×4 cubic supercell (128 atoms/cell) was used formodeling. In the Fe–Ga alloy with an A2 structure(Fig. 1(a)), the probability of finding Ga atoms atneighboring sites is negligible. There are two types of
Fe atoms in the Fe–Ga alloy: those with Ga atoms in
the nearest-neighbouring positions (Fe(1)) and thosewith Ga atoms in the next-nearest-neighbouring
positions (Fe(2)). The fundamental difference is thatthe density of antibonding d-states (DOS) on atoms of
the Fe(1) type is much higher than that on atoms of
the Fe(2) type. We focused on two limiting
configurations, referred to as structures A and B. The
Fe(1) atom was replaced, and there were no Ga atoms
around the dopant (type A, Fig. 1(b)). The Fe(2) atomwith four Ga atoms in the nearest neighboring
positions was substituted (type B, Fig. 1(c)).
The simulation revealed two factors that affectedmagnetostriction [1]. First, it was energeticallyfavorable for TM and La atoms to have a different
local environment relative to atoms of the host lattice.
The La atom preferentially occupied a position in thelattice surrounded only by Fe atoms, whereas TM
atoms occupied sites in a local environment of four Fe
atoms and four Ga atoms. The atoms closest to theFig. 1(a) Atomic configuration of Fe84.4Ga14.8X0.8. Local
atomic ordering around the dopant atoms in first andsecond coordination spheres for structures of (b) type A
and (c) type B.

dopant Fe atoms had different electronic properties.
Second, the Fe atoms of the first and second
coordination shells changed their electronic
properties differently, depending on the type of local
ordering and impurities. The increase inmagnetostriction owing to the antibonding nature of
the Fe-TM bond was partially compensated by adecrease in DOSFe(d) (type A ordering) or a low
DOSFe(d) (type B) near the Fermi level. The stronger
bonding nature of the interaction between the Featoms of the first and second coordination spheres
also reduced λ001. In La-doping, the La–Fe bond hasa binding character in the local ordering of type A andantibonding in structure B. Because the Fe-Fe
interaction between atoms in the dopant’s first andsecond coordination spheres is antibonding, it should
enhance λ001. The results obtained explained theexperimental observations.
References[1] T. Inerbaev, A. Abuova, Y. Kawazoe, and R. Umetsu, Comp.
Mater. Sci. 202, 110934 (2022).

Talgat Inerbaev (Corresponding Author, L.N. Gumilyov Eurasian National University)
E-mail: talgat.inerbaev@gmail.com
Momoji Kubo (Head of Center for Computational Materials Science)
E-mail: momoji@tohoku.ac.jp
URL: http://www.sc.imr.tohoku.ac.jp/eng/

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Post-Growth Annealing Effect on Electronic State in T’-Type R2CuO4
Center of Neutron Science for Advanced MaterialsA

mong the single-layer R2CuO4 (R: rare earth) with three structural isomers, the T-type cuprate with four oxygen atoms
coordinated around the Cu ion exhibits superconductivity due to post-growth annealing. Therefore, it is essential to clarify the roleof annealing in the ground state. Here, we studied the annealing effects on the electronic state by X-ray scattering measurements
and revealed that the anneal-induced doping of electrons in La1.8Eu0.2CuO4 is associated with the appearance of superconductivity.
Superconductivity in cuprate oxides has been
attributed to carrier doping into Mott insulators. However,after the report of superconductivity in R2CuO4 (R : rareearth element) without effective carrier doping, the varietyof ground states in R2CuO4 has attracted tremendous
attention. The importance of the coordination of oxygen
atoms around the Cu ions on the physical properties was
highlighted, and R2CuO4 with a T’-type structure (fouroxygen coordination) can have a metallic ground state.
However, since post-growth annealing treatment isnecessary for the emergence of superconductivity in aT’-type structure, the actual ground state of R2CuO4
remains controversial.
To clarify the role of annealing and the ground stateof R2CuO4, we performed complemental X-ray scattering
measurements on La1.8Eu0.2CuO4 (LECO) and Nd2CuO4(NCO) [1, 2]. The former exhibits superconductivity due
to annealing, whereas the latter is a non-superconductor
even after annealing. Therefore, a comparison of theresults would provide crucial information.
Figure 1 shows the Cu L3 -edge resonant inelastic
X-ray scattering (RIXS) spectra of the as-grown andannealed NCO. The variation in the spectra due toannealing is quite similar to that induced by Ce doping,suggesting electron doping in the annealing procedure.
Consistent results for NCO were obtained using Cu
K-edge X-ray absorption near-edge structure (XANES)
measurements (Fig. 2). However, the spectral change
due to annealing was much more drastic in LECO. The
number of induced electrons due to annealing is ~0.4
and ~0.05 per Cu atoms in LECO and NCO, respectively,
while the removed oxygen value is comparable [3]. These
results suggest distinct electron-doping processes in thetwo compounds and that a variation in the electronic
band structure causes self-doping of carriers in LECO.

Fig. 1 Cu L3 -edge RIXS spectra of as-grown and annealed
Nd2-x Cex CuO4 with x = 0 [1].

References[1] K. Ishii, S. Asano, M. Ashida, M. Fujita, B. Yu, M. Greven, J. Okamoto,D.-J. Huang, and J. Mizuki, Phys. Rev. Materials 5, 024803 (2021).
[2] S. Asano, K. Ishii, D. Matsumura, T. Tsuji, K. Kudo, T. Taniguchi, S.

Fig. 2 Cu K-edge XANES spectra of as-grown andannealed La1.8Eu0.2CuO4 and Nd2CuO4 [2].

Saito, T. Sunohara, T. Kawamata, Y. Koike, and M. Fujita, Phys. Rev. B
104, 214504 (2021).
[3] M. Fujita, T. Taniguchi, T. Wang, S. Torii, T. Kamiyama, K. Ohashi, T.

Kawamata, T. Takamatsu , T. Adachi, M. Kato, and Y. Koike, J. Phys.
Soc. Jpn. 90, 105002 (2021).

Masaki Fujita (Head of Center of Neutron Science for Advanced Materials)
E-mail: masaki.fujita.b5@tohoku.ac.jp
URL: http://nc-imr.imr.tohoku.ac.jp/index-e.html

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Editors
 yuta Kasada, Yoshinori Onose, Rie Umetsu, R
Shigeyuki Takagi, Haruhiko Morito, and
Motomichi Koyama

Editorial Staff
Misa Y. Tomimatsu, Aki Oikawa, and Yuko Godart

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