KINKEN
Research Highlights
2018

Institute for Materials Research, Tohoku University

KINKEN Research Highlights 2018
Contents
Preface���������������������������������������������������������������������������������������������������������������������������������������������������������� 4

Research Highlights

1. Infrastructural Materials
Crystal Physics Division������������������������������������������������������������������������������������������������������������������������������� 8
Microstructure Design of Structural Metallic Materials Division�������������������������������������������������������������������� 9
Materials Design by Computer Simulation Division������������������������������������������������������������������������������������ 10
Environmentally Robust Materials Division��������������������������������������������������������������������������������������������������11
Chemical Physics of Non-Crystalline Materials Division���������������������������������������������������������������������������� 12
Deformation Processing Division��������������������������������������������������������������������������������������������������������������� 13
Analytical Science Division������������������������������������������������������������������������������������������������������������������������ 14
Creation of Life Innovation Materials for Interdisciplinary and International Researcher Development������ 15

2. Energy-Related Materials
Physics of Crystal Defects Division������������������������������������������������������������������������������������������������������������ 18
Irradiation Effects in Nuclear and Their Related Materials Division������������������������������������������������������������ 19
Physics of Electronic Materials Division����������������������������������������������������������������������������������������������������� 20
Structure-Controlled Functional Materials Division������������������������������������������������������������������������������������� 21
Non-Equilibrium Materials Division������������������������������������������������������������������������������������������������������������� 22
Hydrogen Functional Materials Division����������������������������������������������������������������������������������������������������� 23
Advanced Crystal Engineering Laboratory������������������������������������������������������������������������������������������������ 24
Multi-Functional Materials Science Division����������������������������������������������������������������������������������������������� 25

3. Electronic Materials
Theory of Solid State Physics Division������������������������������������������������������������������������������������������������������� 28
Magnetism Division������������������������������������������������������������������������������������������������������������������������������������ 29
Surface and Interface Research Division��������������������������������������������������������������������������������������������������� 30
Low Temperature Physics Division������������������������������������������������������������������������������������������������������������� 31
Low Temperature Condensed State Physics Division�������������������������������������������������������������������������������� 32
Quantum Beam Materials Physics Division������������������������������������������������������������������������������������������������ 33
Solid-State Metal-Complex Chemistry Division������������������������������������������������������������������������������������������ 34
Magnetic Materials Division������������������������������������������������������������������������������������������������������������������������ 35
Crystal Chemistry Division������������������������������������������������������������������������������������������������������������������������� 36
Actinide Materials Science Division����������������������������������������������������������������������������������������������������������� 37
Materials Science of Non-Stoichiometric Compounds Division����������������������������������������������������������������� 38
Professional development Consortium for Computational Materials Scientists (PCoMS)�������������������������� 39

Research Centers
International Research Center for Nuclear Materials Science�������������������������������������������������������������������� 42
Cooperative Research and Development Center for Advanced Materials������������������������������������������������ 44
High Field Laboratory for Superconducting Materials�������������������������������������������������������������������������������� 45
Trans-Regional Corporation Center for Industrial Materials Research������������������������������������������������������� 46
Center for Computational Materials Science���������������������������������������������������������������������������������������������� 47
Collaborative Research Center on Energy Materials���������������������������������������������������������������������������������� 48
International Collaboration Center (ICC-IMR)��������������������������������������������������������������������������������������������� 49
Center of Neutron Science for Advanced Materials����������������������������������������������������������������������������������� 50
Laboratory of Low Temperature Materials Science������������������������������������������������������������������������������������ 51
Laboratory of Alpha-Ray Emitters�������������������������������������������������������������������������������������������������������������� 52
Analytical Research Core for Advanced Materials������������������������������������������������������������������������������������� 53

Author Index����������������������������������������������������������������������������������������������������������������������������������������������� 54

Keyword Index������������������������������������������������������������������������������������������������������������������������������������������� 55

Preface

Dear Colleagues,

We are pleased to present KINKEN Research Highlights 2018, 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 celebrated its centenary in 2016. Professor Kotaro Honda established the IMR at the Tohoku
Imperial University in 1916 as the 2nd Division of the Provisional Institute of Physical and Chemical
Research. At that time the primary research focus was steel. Thereafter, the research domains graduallybroadened to include various types of alloys and metals. The name was changed into the ResearchInstitute for Iron, Steel and Other Metals (RIISOM) in 1922. Subsequently, the institute developed into a
global center for fundamental and applied research covering all types of materials, including nonmetals.
In 1987 the institute was reorganized into a national collaborative research institute affiliated with Tohoku
University, and consequently renamed to the present Institute for Materials Research (IMR).

IMR has greatly contributed to the advancement of materials science and engineering. The inventionof KS steel in 1916, the strongest permanent magnet at that time, was the first great achievement. In
subsequent years, many different types of practically useable materials have successfully beendeveloped, including new KS steel, Sendust alloy, SiC fibers, various intermetallic compounds, andmore recently, amorphous alloys. In addition, considerable effort was dedicated to basic research formaterials development, which paved the way for pioneering research in magnetism, superconductivity,

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IMR KINKEN Research Highlights 2018

Director Prof. Koki Takanashi

optical properties, and microstructure analyses of materials. Recently, IMR has created a wide array of
new materials, including high-performance, high-quality, and multifunctional materials such as bulk
metallic glasses, nanostructured materials, nanocomposites, ceramics, crystals, oxides, nitrides,
hydrides, complexes, organic materials, etc., which are useful for electronic, optical, magnetic, spintronic,
biological, energetic, and infrastructural applications.

In the 21st Century, we face worldwide environmental problems such as global warming and thedepletion of resources and energy. There is an increasing need to preserve the environment and work
towards achieving sustainable societies. IMR upholds these themes with the objective of “contributing
to the well being of the human race and the development of civilization through the creation of newmaterials that are truly useful to society”.

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 20185

Infrastructural Materials

IMR KINKEN Research Highlights 2018

Research

Infrastructural Materials

Subgrain Boundary Energy of Copper at Melting Temperature

Grain boundary energy influences the morphology of the crystal/melt interface of polycrystalline materials
during solidification. However, it is quite hard to experimentally measure the grain boundary energy of metals
at their melting temperature. We overcame the experimental difficulties and determined the grain boundary
energy of copper by an in-situ observation method.

The shape of the grain boundary groove isdetermined by the force balance between the
crystal/melt interface energy (σsl) and the grainboundary energy (σgb). Therefore, if we could
observe the grain boundary groove at an equilibrated
crystal/melt interface, we could measure σgb at themelting temperature. In this study, we attempted todirectly observe the grain boundary groove at the
crystal/melt interface in pure copper (Cu).
The experiment was conducted with an in-situ
observation system consisting of a furnace and adigital optical microscope.
Figure 1 shows the morphological change in
the grain boundary groove during the directional
solidification of pure Cu [1]. Clearly, the groove
gradually deepened, and its shape changed. This
indicated that we had to maintain the interface underequilibrium conditions to be able to measure σgbfrom the groove shape. Thus, we attempted to keep
the interface in equilibrium. If, for an extended
period of time, the crystal/melt interface does not
move, melt, or grow, the interface can be assumed
to be at the melting temperature.
Thus, we adjusted the temperature precisely bymonitoring the crystal/melt interface. Figure 2 shows
the stationary crystal/melt interface [1]. To determine
the shape of the groove, the contrast and brightnessof each image was changed prior to the analysis.
It was shown that the position of the planarinterface did not change, which indicated that thetemperature at the crystal/melt interface wasmaintained at the melting temperature of Cu (1358 K).
The shape of the grain boundary groove is determinedby the force balance indicated in Fig. 2, which can be
expressed as σgb = (cosθ 1 + cosθ 2) σsl.
The crystal/melt interfacial energy of Cu at its
melting temperature was reported to be σsl =0. 2724
(J m−2), and θ 1 and θ 2 could be measured from theimages in Fig. 2. Thus, we could estimate σgb. The
observed grain boundary was found to be a
subgrain boundary by electron backscattering
pattern analysis. The values of the σgb estimates arelisted in Fig. 2. The estimates of σgb (subgrainboundary) ranged between 0.234 and 0.296 J m−2.
Keywords: crystal growth, interface
Kozo Fujiwara (Crystal Physics Division)
E-mail: kozo@imr.tohoku.ac.jp
URL: http://www.xtalphys.imr.tohoku.ac.jp/

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IMR KINKEN Research Highlights 2018

Fig. 1 Grain boundary groove during the directional
solidification of pure Cu.

Fig. 2 (left) Equilibrated crystal/melt interface. (right)
Measurement of grain boundary energy.

In this way, the equilibrated crystal/meltinterface with a grain boundary groove wasestablished by controlling the temperature throughmonitoring the sample state, which enabled themeasurement of the grain boundary energy, σgb.
References[1] K. Maeda, A. Niitsu, H. Morito, K. Shiga, and K. Fujiwara, Scr.
Mater. 146, 169 (2018).

IMR KINKEN Research Highlights 2018

Influence of Driving Force for Precipitation on Dispersion of
Vanadium Carbide Interphase Precipitation in Low-Carbon Steels

As a controlling factor on the dispersion of nanosized interphase precipitation formed at the migrating ferrite/
austenite interface during ferrite transformation, the driving force for its precipitation is estimated in this study
by quantitatively measuring the interfacial composition in vanadium-microalloyed low-carbon steels. Following
our expectation, the estimated driving force shows good correlation with both the number density and averageradius of vanadium carbide.

The interphase precipitation of nanosized alloy
carbide occurs at the migrating ferrite/austenite
interface during ferrite transformation in steels
containing strong carbide-forming elements, e.g.,
vanadium, niobium, or titanium. Compared withnormal precipitation by aging from a supersaturated
matrix, interphase precipitation features rapid
precipitation kinetics, facilitated by both local
enrichment in the solute and higher diffusivity at theinterphase boundary.
In this study, we try to correlate the driving force
for interphase precipitation with the resultant
dispersion of nanosized alloy carbide in vanadiummicroalloyed low-carbon steels. The driving force
was quantitatively estimated based on the interfacialcomposition measured by using electron probe
microanalysis. In order to eliminate the influence ofinterfacial coherency [1], only ferrite grains without aspecific highly coherent orientation relationshipwere purposely selected to quantify the dispersionof vanadium carbide interphase precipitation byatomic probe tomography.
Figure 1 shows a vanadium atom map of ferrite
with nanosized vanadium carbide as a typicalexample of interphase precipitation. Figure 2 shows
the variations in number density and average radiusof vanadium carbide with estimated driving force,
respectively, which is formed under various
conditions, e.g., at different transformation
temperatures or with different bulk alloy
compositions. The overall tendency can besummarized as: interphase precipitation increases
in number density and decreases in size with larger
driving force, which is reasonable from the viewpointof facilitated nucleation [2]. Based on this result, thestrategy for further strengthening the interphase
precipitation-strengthened automobile steels should
be refinement in particle dispersion by increasing
the driving force through better alloy design andprocessing.

Fig. 1 Typical vanadium atom map of ferrite with vanadium
carbide interphase precipitation.

(a)

(b)

Fig. 2 Relationship between (a) number density and (b)average radius of vanadium carbide with driving force
for interphase precipitation formed under various
conditions.

References[1] Y.-J. Zhang, G. Miyamoto, K. Shinbo, and T. Furuhara, Scr.
Mater. 69, 17 (2013).
[2] Y.-J. Zhang, G. Miyamoto, K. Shinbo, and T. Furuhara, Acta
Mater. 128, 166 (2017).

Keywords: phase transformation, interface, steel
Yongjie Zhang (Microstructure Design of Structural Metallic Materials Division)
E-mail: yongjie@imr.tohoku.ac.jp
URL: http://www.st-mat.imr.tohoku.ac.jp

IMR KINKEN Research Highlights 20189

Infrastructural Materials

Superlarge-Scale Molecular Dynamics Simulation for
Fracture of Materials

T

he novel development of high-performance and long-life materials needs a deep understanding of thefracture processes of materials. These processes consist of multiphysics and multiscale phenomena including
chemical reactions on the nanoscale and physical phenomena such as friction, impact, stress, and fluid on themacroscale. We are pioneering advanced materials design based on superlarge-scale simulation for the
elucidation of multiphysics and multiscale phenomena.
To realize a safe and secure society, the novel
development of high-performance and long-lifematerials is necessary. These material technologies
require a deep understanding of fracture processes,
which consist of multiphysics and multiscale
phenomena including chemical reactions on thenanoscale and physical phenomena such as
friction, stress, and fluid on the macroscale. Thus,
we have investigated multiphysics and multiscale
phenomena by computational simulation methods.
[1-3] Here, superlarge-scale simulations canprecisely elucidate the multiphysics and multiscale
phenomena in the fracture process. Then, weapplied our superlarge-scale molecular dynamics
code for pioneering next-generation materials
design.
In order to reveal fracture processes of thelamellar structure in polyethylene, we performedcoarse-grained
superlarge-scale
molecular
dynamics simulations, which can be directlycompared with electron microscopy images. Here,we constructed a large-scale lamellar structure
consisting of three million monomers (Fig. 1). While
stretching parallel to the crystal direction, thestructural change from amorphous to crystalline
layers increases the compression and the generationof voids in the amorphous layers. We found that thechange in the polymer lamella structure lowers thestress in the polymer materials [1].
Ni sintering in the Ni/YSZ porous anode of asolid oxide fuel cell changes the porous structure,
leading to degradation. To prevent the sintering anddegradation, we need to elucidate the effects of theparticle size on sintering. In this study, we developed
a superlarge-scale molecular dynamics simulator
with a multimillion-atom Ni/YSZ multi-nanoparticle
model and investigated the effects of YSZ particle
size on the sintering and degradation in the Ni/YSZ
anodes. At first, we compared the sinterng
processes in the Ni/YSZ models with YSZ particle
diameters of 6 and 2 nm. When the diameter is 6

Fig. 1 Fracture simulation of polymer lamella structure withthree million monomers.

Fig. 2 Snapshots of Ni sintering simulations of themultimillion-atom Ni/YSZ multi-nanoparticle model withYSZ particle diameter of 6 nm.

nm, some Ni nanoparticles form a large compact
aggregate owing to sintering (Fig. 2). Moreover, thepores in the Ni/YSZ multi-nanoparticle model
coalesce because of the sintering and the diffusion
path of hydrogen gas is blocked. In contrast, when
the diameter is 2 nm, pore coalescence is notobserved. Thus, we found that the gas diffusion
performance degrades as the YSZ particle size
increases [2].
References[1] Y. Higuchi and M. Kubo, Macromolecules. 50, 3690 (2017).
[2] J. Xu, Y. Higuchi, N. Ozawa, K. Sato, T. Hashida, and M. Kubo,
ACS Appl. Mater. Interfaces. 9, 31816 (2017).
[3] Y. Wang, J. Xu, Y. Ootani, S. Bai, Y. Higuchi, N. Ozawa, K.
Adachi, J.M. Martin, and M. Kubo, ACS Appl. Mater. Interfaces.
9, 34396 (2017).

Keywords: simulation, molecular dynamics, fracture
Momoji Kubo (Materials Design by Computer Simulation Division)
E-mail: momoji@imr.tohoku.ac.jp
URL: http://www.simulation.imr.tohoku.ac.jp/

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IMR KINKEN Research Highlights 2018

IMR KINKEN Research Highlights 2018

Hydrogen Uptake Under Conventional Electrochemical
Hydrogen Charging

H

ydrogen uptake behaviors under galvanostatic and potentiostatic hydrogen charging conventionally used
for hydrogen embrittlement studies have been examined by using an electrochemical hydrogen permeation
technique. A guideline for efficient hydrogen charging covering a wide range of hydrogen content by changing
the catalyst poison concentration and current density or potential has been obtained.
Electrochemical hydrogen charging is commonly
utilized in order to charge specimens of highstrength steels and other metals with hydrogen for
the examination of their hydrogen embrittlement
properties, owing to its ease and low cost.
Furthermore, cathodic hydrogen charging has ahigh fugacity of hydrogen compared to that in highpressure hydrogen gas at high temperature.
However, the details of the procedures of hydrogencharging are barely reported, and the hydrogencontent in specimens is often controlled in a trialand-error manner.
To understand the hydrogen uptake behavior
underelectrochemicalhydrogencharging
conditions, we adopted an electrochemicalhydrogen permeation technique using pure Fe
sheet specimens in some conventionally usedaqueous solutions with varied concentrations of
NH4SCN, which enhances hydrogen entry.
Figure 1 shows that various hydrogen
permeation current densities can be obtained bycontrolling the hydrogen charging current density[1] or potential [2], and NH4SCN concentration.
Essentially, the hydrogen permeation current
density varies with the logarithm of the current
density and similarly with potential, because thelogarithm of the current density and potential on thehydrogen input side are linearly related, suggesting
a potential-dependent surface coverage ofadsorbed hydrogen.
Because the hydrogen permeation current
density is considered to be proportional to the
diffusible hydrogen content, the resulting hydrogencontent for any given hydrogen charging condition
can be estimated if the hydrogen content obtainedin one condition is measured by means of thermal
desorption analysis. Therefore, the relationships canbe used as a guideline for hydrogen charging.
However, the hydrogen permeation current
density tended to increase with time in a NH4SCNcontaining solution during both galvanostatic andpotentiostatic hydrogen charging, suggesting that it

Fig. 1 Relationship between hydrogen permeation current
density and logarithm of applied current density (top)and applied potential (bottom) of hydrogen input sidefor galvanostatic and potentiostatic hydrogen charging,in various aqueous solutions with/without NH4SCN.

is recommended to measure the resulting hydrogencontent by means of thermal desorption analysis for
accuracy, although the obtained relationship can beused as an approximate standard.
References[1] E. Akiyama and S. Li, Corros. Rev. 34, 103 (2016).
[2] E. Akiyama and S. Li, ECS Trans. 75, 22 (2017).

Keywords: corrosion, high-strength steel, surface reaction
Eiji Akiyama (Environmentally Robust Materials Divison)E-mail: akiyama@imr.tohoku.ac.jp
URL: https://akiyamaimr.amebaownd.com/

IMR KINKEN Research Highlights 201811

Infrastructural Materials

Crystal Structure of C-AlRuNi with Pseudo-Mackay ClusterThe structure of C-AlRuNi (1/0 approximant) is composed by the alternative linkage of the type-A pseudoMackay cluster (pMC-A) and the mini-Bergman cluster (mini-BC) with a regular Al-icosahedron (Al-IC). The
chemical variation of a series of 1/0 approximants is also discussed by using the unique shell structure of pMCs.
Mackay clusters and mini-Bergman clusters(mini-BCs) are common building units for the
icosahedral phase and their distribution provides aninteresting overview of the structures of crystalline
approximants. As an example, recent analyses of
R-AlPdCo and F-AlPdCoGe [1-2] demonstrated theunique linkage of pseudo-Mackay clusters (pMCs)
and mini-BCs connected by sharing the edges of
their inner heavy metal icosahedra (HM-ICO).
Knowledge of the approximant structures also
allows us to suggest the importance of an Al
icosahedron with a TM center (Al-ICO) as a glue unit
in the connection of pMCs.
In the phase diagrams of Al–(Cu, Ni, or Pd)–
(Co, Ru, Rh, Fe, or Ir), three types of 1/0 cubic
approximants (C, C1, and C2) were recognized in
the composition range of 60–80mol% Al. The C
phase is located in the relatively Al-rich and HMpoor region compared to that for the C2 phase, andthe C1 phase is realized in the middle region. Thisfinding strongly suggests a significant relationshipbetween the crystal structures and the chemicalcompositions of these approximants.
The structure of C-AlNiRu [3] is composed of a
3-D framework consisting of the regular heavy metal
icosahedron (H-rICO) and a rather irregular shapedone (H-iICO), as shown in Fig. 1. H-rICO has theinner shell of an Al-cube with a heavy metal centerand the outer shell of an Al-icosi-dodecahedron,indicating an atomic arrangement similar to pMC.
However, H-iICO has an inner shell of an Al-ICO
and could be ranked by mini-BC. In other words,
pMC is located at the origin of the unit cell and theglue unit of an Al-ICO with a Ni center is located at
the center of the unit cell.
It is interesting to note the chemical composition
for the 1/0 approximants by using the structuralvariation of pMCs. The atomic arrangement of theinner shell of pMCs could be classified into three
types (hereafter pMC-A, pMC-B, and pMC-C) [1-2].
The pMC-A type has an Al-polyhedron with a HM
center, pMC-B shows a harmony of an Al-cube andan octahedron of HM and Al, and pMC-C has arather distorted Al icosahedron. The pMC of theFig. 1 Linkage of the two types of heavy metal icosahedra.

Fig. 2 Shell structure of pseudo-Mackay cluster and miniBergman cluster.

C-phase is categorized as pMC-A and this structuralfeature is attributed to the relatively Al-rich nature of
the C-phase. On the contrary, the HM-rich pMC-B
could be found in the structures of the C1 and C2
phases, and the unique arrangement of pMC-A andpMC-B leads to the chemical and structuralvariations of the 1/0 approximants.
References[1] R. Simura, S. Suzuki, K. Yubuta, and K. Sugiyama, Mater.
Trans. 54, 1385 (2013).
[2] K. Sugiyama, K. Yubuta, Y. Yokoyama, S. Suzuki, and R.
Simura, Acta Phys. Pol. A 126, 588 (2014).
[3] R. Simura, K. Sugiyama, S. Suzuki, and T. Kawamata, Mater.
Trans. 58, 1101 (2017).

Keywords: X-ray diffraction (XRD), crystal structure, quasicrystal,
Kazumasa Sugiyama and Rayko Simura (Chemical Physics of Non-Crystalline Materials Division)
E-mail: kazumasa@imr.tohoku.ac.jp
URL: http://www.xraylab.imr.tohoku.ac.jp/

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IMR KINKEN Research Highlights 2018

IMR KINKEN Research Highlights 2018

Strengthening of Biomedical Co−Cr−Mo Alloys by
Introducing Stacking FaultsT

he strengthening of biomedical Co−Cr−Mo alloys is of crucial importance to the improvement of the durabilityof orthopedic implants. Here, we demonstrate for the first time that a substantial increase in the number ofstacking faults occurs during multipass hot deformation, resulting in a significant strengthening of the alloys.
Owing to their superior corrosion and wear
resistance, Co−Cr−Mo alloys are widely used inorthopedic implants such as artificial hip joints andspinal systems. Recently, much attention has been
paid to the strengthening of these alloys to improvethe durability of such implants. We recently reported
that a superior combination of high yield strength(~1.5 GPa) and good ductility (>10%) can beachieved by multipass hot rolling [1]. In this study,
we evaluated the hot-rolled microstructures using
an advanced X-ray diffraction line-profile analysis
based on the extended convolutional multiple whole
profile (eCMWP) fitting to analyze the relevant
strengthening mechanisms [2].
Figure 1 shows the results of the eCMWP
analysis of the hot-rolled specimens, plotted as afunction of the applied equivalent strain (εeq). As
shown in Fig. 1(a), the dislocation density (ρdis) firststrongly increased with εeq and then became
saturated to a very high dislocation density of 8.5 ×1015 m−2 at εeq = 2.66. In contrast, the stacking fault(SF) probability (PSF) was almost zero up to εeq =0.41 and then increased sharply with further
increases in εeq (Fig. 1(b)). PSF was substantiallyhigher at εeq = 2.66, reaching approximately 1.6%.
Using the eCMWP results, we ascertained thecontribution of SFs (σSF) to the yield stress of the
prepared specimens at different values of εeq (Fig.
2). A physical model, which was proposed for hcp
Mg alloys [3], was used to evaluate the SF
strengthening. The σSF was not evident in the initialand εeq = 0.41 specimens, but became significant atgreater εeq. Surprisingly, the σSF finally reachedapproximately 500 MPa, which is superior to thosefrom the other strengthening mechanisms
considered. These results shed light on theimportance of the SF strengthening, which has not
yet been directly considered in these alloys, and will
help in guiding the design and manufacturing
strategy for high-strength Co−Cr−Mo alloys using
lattice defects.

Fig. 1 Results of eCMWP analysis of the multipass hotrolled specimens

Fig. 2 Contributions of grain boundaries (σGB), dislocations(σdis), and stacking faults (σSF) to the yield stress of themultipass hot-rolled specimens.

References[1] M. Mori, K. Yamanaka, S. Sato, S. Tsubaki, K. Satoh, M.
Kumagai, M. Imafuku, T. Shobu, and A. Chiba, Acta Biomater.
28, 215 (2015).
[2] K. Yamanaka, M. Mori, S. Sato, and A. Chiba, Sci. Rep. 8,10808 (2017).
[3] W. W. Jian, G. M. Cheng, W. Z. Xu, H. Yuan, M. H. Tsai, Q. D.
Wang, C. C. Koch, Y. T. Zhu, and S. N. Mathaudhu, Mater. Res.
Lett. 1, 61 (2013).

Keywords: alloy, defects, strength
Kenta Yamanaka and Akihiko Chiba (Deformation Processing Division)
E-mail: k_yamanaka@imr.tohoku.ac.jp
URL: http://www.chibalab.imr.tohoku.ac.jp/

IMR KINKEN Research Highlights 201813

Infrastructural Materials

Emission Characteristics of 6.78-MHz Radio-Frequency
Glow Discharge Plasma in a Pulsed ModeBoltzmann plots for atomic emission lines of iron in an argon glow discharge plasma driven by a 6.78-MHz
radio-frequency (RF) voltage in a pulsed operation were investigated to discuss how the excitation/ionization
process was affected by the pulsation. The excitation temperature was obtained in a narrow range of 3300–
3400 K, which was hardly affected by the duty ratio of the pulsed RF glow discharge plasma.
Glow discharge optical emission spectrometry (GDOES) is extensively employed for the direct analysis of solid
samples, because the glow discharge plasma is self-sustained
under a stable condition, which can provide the emission
spectra with small intensity variations as well as with low
background levels. GD-OES can be operated using both
direct-current (DC) and radio-frequency (RF) power supplies;in particular, the latter can contribute to wider analyticalapplications of GD-OES, principally because it enables
nonconductive samples to be analyzed. In this study [1], weselected a driving frequency of 6.78 MHz for an RF excitation
source in GD-OES, mainly because it has a larger self-bias
voltage than that of 13.56 MHz and thus may provide larger
numbers of samples sputtered into the plasma.
The concept of local thermodynamic equilibrium (LTE)is described as follows: a plasma in the LTE state ischaracterized by a unique temperature that can be determinedby a Maxwell-like distribution of collision partners in adominant thermal collision of the first kind, such as collisions
with energetic electrons. In this case, excitation and ionization
processes occurring in the LTE plasma, resulting in theemission spectrum, could be predicted from the Boltzmann
distribution among the corresponding excited energy levels.
However, glow discharge plasma is not in an LTE condition
and thus the excitation/ionization phenomena in GD-OES
cannot be explained from the Boltzmann distribution. Our
previous studies indicated that deviations from the Boltzmann
distribution, which were observed in both atomic and ionicemission lines of iron, gave useful information on the excitation/
ionization processes in argon GD-OES [2, 3]. In the analysisof the iron atomic lines, it was found that the excited energy
levels of the iron atom above ca. 6 eV were more populated
than a Boltzmann distribution over excitation energies of 3.4–
4.6 eV, probably through stepwise de-excitation processes
from higher energy levels [2].
This paper discusses Boltzmann plots for both atomic
and ionic emission lines of iron, when a pulsed 6.78-MHz
glow discharge plasma is employed, in comparison to thecontinuous RF mode. Few studies have been publishedregarding the plasma diagnostics of 6.78-MHz RF glow
discharge in a pulsed mode. The objective of this study is toconsider the Boltzmann distribution of iron emission lines inFig. 1 Variation in the excitation temperature as a functionof the duty ratio in the pulsed RF glow discharge plasma
at a pulse frequency of 77 Hz.

order to understand how their characteristics can be
explained by the excitation mechanism of iron species in thepulsed RF glow discharge plasma.
The excitation temperature in the pulsed RF plasma canbe estimated from the slope of the linear part, the excitationenergy of which ranges from 3.3 to 4.3 eV in the Boltzmann
plot. Figure 1 shows a variation in the excitation temperaturewhen different duty ratios (ratio of the power-on period to thepulse width) are selected at a pulse frequency of 77 Hz in an
Ar plasma of 530 Pa, and then the excitation temperature
became almost unchanged (ca. 3350 K), whereas the net
emission intensities were drastically reduced at lower duty
ratios. This effect implied that a glow discharge plasma could
be sustained by a self-stabilized negative glow zone in which
the kinetic energy of the electron would be hardly changed
under a uniform potential distribution. , thus determining theexcitation of iron atoms principally.
References[1] X. Zhang and K. Wagatsuma, Spectrochim. Acta Part B 133, 72 (2017).
[2] L. Zhang, S. Kashiwakura, and K. Wagatsuma, Spectrochim. Acta Part B
66, 785 (2011).
[3] L. Zhang, S. Kashiwakura, and K. Wagatsuma, Spectrochim. Acta Part B
67, 24 (2012).

Keywords: atomic emission spectrometry, glow discharge plasma, plasma diagnostic
Kazuaki Wagatsuma (Analytical Science Division)
E-mail: wagatuma@imr.tohoku.ac.jp
URL: http://wagatsuma.imr.tohoku.ac.jp/

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IMR KINKEN Research Highlights 2018

Preparation of Bioactive Porous Surfaces in Biomedical
Co-Cr-Mo AlloyN

ano- or submicron porous surfaces can significantly enhance cell attachment, which accelerates theformation of new bone tissue. We recently presented a novel method for preparing such porous surfaces inbiomedical Co-Cr-Mo alloy, which involves local dealloying in a pure Zn melt and selective removal of the Znrich phase formed in the dealloying products.
Biomedical Co-Cr-Mo (CCM) alloys have been
widely used in orthopedic implants such as artificial
knee and hip joints. Nevertheless, they are
considered inferior to Ti-based alloys in terms ofosseointegration and bone anchorage, for which
chemical and electrochemical methods are
generally utilized for introducing nano/submicron
porous surface structures.
We designed a novel method to prepare Znincorporated nano/submicron porous surface
structures in CCM alloy by a combination of local
dealloying and selective dissolution [1]. First, areaction layer was formed by a dealloying reactionof CCM alloy in Zn melt, which was significantly
affected by the dealloying temperature and period.
Co in the alloy was selectively dealloyed, anddispersoids and filamentary structures were formed,
which grew vertically from the CCM matrix, as
shown in Fig. 1(a).
Two types of phases with different compositions
are evident; one phase is rich in Co and Zn (Zn-richphase), and the other phase is rich in Co and Cr(Zn-lean phase). According to Figs. 1(a) and 1(b),the compositions of the Zn-rich and Zn-lean phases
are Co-Cr2.3–2.8 -Mo0.3–0.8 -Zn45–47 (wt.%) and CoCr36–39 -Mo8–10 -Zn4–9 (wt.%). A portion of the Zn
atoms diffused into the CCM matrix and formed acompound of Co-Cr22-Mo2.6 -Zn9.7 (wt.%).
Homogeneous porous structures are produced
by selectively dissolving the Zn-rich phase, as
shown in Fig. 1(c). The pores are on the submicronscale, and the thickness of the porous structure isapproximately 4 μm. The bioactivity of CCM alloy is
expected to be improved by the porous surfaces
introduced in present study, because the roughsurfaces generally resulted in enhanced cellattachment onto biomaterial surfaces.
References[1] D. Wei, Y. Koizumi, and A. Chiba, Mater. Lett. 219, 256 (2018).

Fig. 1(a) Cross-sectional STEM-HAADF (high-angle
angular dark field scanning transmission electron
microscopy) image of CCM alloy dealloyed in a pure Zn
melt at 800 °C for 5 h; (b) corresponding EDS (energy
dispersive X-ray spectrometry) line scan along the redarrow; (c) SEM (scanning electron microscope) imageof CCM alloy surface after dealloying in pure Zn melt
and subsequent selective dissolution [1].

Keywords: surface reaction, nanostructure, corrosion
Daixiu Wei (Creation of Life Innovation Materials for Interdisciplinary and International Researcher Development)
E-mail: wei1987xiu@imr.tohoku.ac.jp
URL: http://life-pro.imr.tohoku.ac.jp/index.html

IMR KINKEN Research Highlights 201815

Energy-Related Materials

IMR KINKEN Research Highlights 2018

Research

Energy-Related Materials

Origin of Resistance at Si/GaAs Heterointerfaces for Tandem Solar
Cells Fabricated by Surface-Activated Bonding at Room TemperatureThe intrinsic microstructure of Si/GaAs heterointerfaces for tandem solar cells, fabricated by surface-activatedbonding at room temperature, is examined. The bonded heterointerfaces include an arsenic-deficient crystalline
GaAs layer and an amorphous Si layer of approximate thicknesses less than 1 nm and 3 nm, respectively,
introduced by the irradiation of an argon atom beam for surface activation before bonding. It is hypothesizedthat the intrinsic interface resistance mainly originates from the arsenic-deficient defects in the former layer.
Tandem solar cells consisting of silicon (Si) and
III-V compounds are one of the promising candidates
for next-generation terrestrial photovoltaic systems,
which can surpass the efficiency milestone of 30%
for non-concentrating solar cells without using
expensive Ge or GaAs substrates. Recently, as a
low-cost process, surface-activated bonding (SAB)at room temperature (RT), in which the surfaces ofsubstrates are activated before bonding by creating
dangling bonds via the removal of contaminants
under an energetic particle bombardment in highvacuum (using an argon fast atom beam), has been
applied to form Si/GaAs heterointerfaces for hybrid
triple-junction solar cells with a high conversion
efficiency above 26% [1]. Even though the interface
resistance (~10−1 Ωcm2) is low enough for solar
cells, it is still higher than the ideal value at defectfree heterointerfaces (~10−4 Ωcm2). A comprehensive
understanding of the electrical properties at theheterointerfaces depending on their atomic structure
is indispensable to establish low-cost fabrication
processes of high-efficiency tandem solar cells by
optimizing the interface structure.
In the present work [2], we examined the Si/
GaAs heterointerfaces fabricated at RT under a
SAB condition [1], with the substrates of B-doped(100) p-type Si (with a carrier concentration of
2×1014 cm−3) and Si-doped (100) n-type GaAs
(2×1016 cm−3) which was 5° off from (001) toward[110]. Some of them were then annealed at 673 K for
1 min. The structural properties were determined bytransmission electron microscopy (TEM).
As-bonded heterointerfaces included anarsenic-deficient crystalline GaAs layer less thanapproximately 1 nm thick and an amorphous Si
layer of approximate thickness 3 nm. Dimples wereintroduced on the entire GaAs surface at thebonding heterointerface, via the introduction ofarsenic vacancies during the surface activation
process, and they disappeared after annealing at
673 K. Moreover, small number of dumps due to
Keywords: solar cells, defects, interface
Yutaka Ohno (Physics of Crystal Defects Division)
E-mail: yutakaohno@imr.tohoku.ac.jp
URL: http://lab-defects.imr.tohoku.ac.jp

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IMR KINKEN Research Highlights 2018

Fig. 1 Dark-field TEM of (a) GaAs and (b) Si at aheterointerface taken with the (220) reflection for GaAs
and Si, respectively. The inset in (a) shows thecorresponding electron diffraction. (c, d) Bright-field
TEM of the interface taken with both the (2-20) reflectionsfor Si and GaAs due to (c) a dislocation in GaAs
cropping out the interface and (d) arsenic-deficient
dimples on the GaAs surface. The inset in (c) indicatesthe calculated hydrostatic stress field for dislocations in
GaAs.

dislocations existed on the surface. The density inthe amorphous Si layer was lower than in theconventional amorphous Si, owing to the introductionof Si vacancies during the surface activation
process, and it was recovered by annealing at 673
K. The interface resistance can be reduced bysuppressing those defects via the optimization ofSAB conditions.
References[1] N. Shigekawa, J. Liang, R. Onitsuka, T. Agui, H. Juso, and T.
Takamoto, Jpn. J. Appl. Phys. 54, 08KE03 (2015).
[2] Y. Ohno, H. Yoshida, S. Takeda, J. Liang, and N. Shigekawa,
Jpn. J. Appl. Phys. 57, 02BA01 (2018).

IMR KINKEN Research Highlights 2018

Direct Observation of Deuterium Trapping at Irradiation-Induced
Vacancy Clusters in Tungsten by Positron Annihilation SpectroscopyDeuterium trapping at vacancy clusters in neutron-irradiated tungsten, a primary candidate material for plasmafacing components in fusion reactors, was revealed by positron annihilation spectroscopy. This is the first direct
observation of the potential origin of the significant increase in hydrogen retention in irradiated tungsten.
The development of fusion reactors such as
International Thermonuclear Experimental Reactor(ITER) has been improving. In plasma-facing
components, energetic hydrogen is induced
together with radiation damage due to exposure tofusion plasma. Because tritium is an essential fusion
reaction source, it is necessary to constrain its
retention in the plasma-facing components. Such
constraints are also of great importance from asafety perspective. Tungsten is a primary candidate
material for the plasma-facing components, owing
to its high melting point and high sputtering
resistance to energetic particles. The solubility oftritium in tungsten is very low (the lowest amongmetals), which is an advantage in reducing tritium
retention during the operation of fusion reactors.
However, recent studies have reported that
irradiation causes significant enhancement ofhydrogen retention in tungsten. This is ascribed tohydrogen trapping at irradiation-induced defects
such as vacancies and vacancy clusters; however,it has not yet been clarified. We employed positronannihilation spectroscopy (PAS) to reveal both
irradiation-induced defects and hydrogen inneutron-irradiated tungsten [1].
Pure tungsten (4N) was neutron-irradiated at~573 K for ~40 days to the dose of ~0.3 dpa,
followed by post-irradiation annealing (PIA) at 573 K
for 100 hours. The PIA was performed undervacuum or in deuterium gas at ~0.1 MPa. In the asirradiated state, the formation of vacancy clusters
with the size of ~V40 was revealed by positron lifetime
measurements. After the PIA in vacuum, the positron
lifetime was almost the same as that in the asirradiated state, indicating no change in the vacancy
clusters. However, after the PIA in deuterium gas,
the positron lifetime was significantly shorter thanthat in the as-irradiated state, strongly suggesting
positron annihilation with deuterium electrons at thevacancy clusters. To analyze the chemical
environment at the positron trapping sites,
coincidence
Dopplerbroadening(CDB)

Fig. 1 Correlation of low- and high-momentum component
fractions of CDB measurements for neutron-irradiatedpure tungsten.

measurements were performed. Figure 1 shows thecorrelation between the low- and high-momentum
fractions in the CDB spectra. It should be noted thatthe correlation point for the PIA in deuterium, shown
as a red point, was not located on the dashed line
connecting the unirradiated and as-irradiated states.
This clearly indicates positron annihilation with
deuterium electrons, and thus deuterium trapping at
irradiation-induced vacancy clusters was revealed.
This gives the first direct observation of deuterium
trapping at irradiation-induced defects, which issuggested to be the main origin of the significant
increase in hydrogen isotope retention in irradiatedtungsten.
References[1] T. Toyama, K. Ami, K. Inoue, Y. Nagai, K. Sato, Q. Xu, and Y.
Hatano, J. Nucl. Mater. 499, 464 (2018).

Keywords: positron annihilation, nuclear materials, vacancy
Yasuyoshi Nagai, Koji Inoue, Yasuo Shimizu, and Kazuaki Nagumo (Irradiation Effects in Nuclear and Their RelatedMaterials Division)
E-mail: nagai@imr.tohoku.ac.jp
URL: http://wani.imr.tohoku.ac.jp/

IMR KINKEN Research Highlights 201819

Energy-Related Materials

Three-Dimensional Imaging of Threading Dislocations in
GaN Using Multiphoton-Excitation PhotoluminescenceThree-dimensional imaging of threading dislocations in GaN was demonstrated by using multiphotonexcitation photoluminescence. Threading dislocations have nonradiative characteristics, and thus these arevisualized as dark lines in the photoluminescence images. This can be considered as a novel method forcharacterizing defects in GaN films without any destructive preparations.
Nitride semiconductors have been widely used
for the applications of optoelectronic devices, suchas blue light-emitting diodes, violet laser diodes,
and high-electron-mobility transistors. Recently, theGaN-based vertical devices have attracted muchattention for hybrid and electric vehicles. Thesevehicles require power electronics to drive highpower motors. GaN-based vertical transistors canachieve both high breakdown voltage larger than 1
kV and low on-resistance. Because these properties
are superior to the current electronic devices basedon Si, GaN-based vertical devices are expected for
power electronics. For fabricating GaN-based
power devices, a GaN wafer with low defect density
is indispensable. Currently, a GaN wafer has been
fabricated from a thick GaN film grown on a foreign
substrate. The density of threading dislocations(TDs) in a GaN depends on the growth method,
growth conditions, and the thickness. To achieve
many fewer TDs in bulk GaN, it is important to clarify
how TDs propagate in GaN crystal. In this study,
multiphoton-excitation photoluminescence, which
does not require special sample preparation, is
proposed to analyze the three-dimensional
distribution of TDs in GaN.
Unintentionally doped n-type c-plane GaN
templates, which are grown by halide vapor phase
epitaxy on a sapphire substrate, are used for themeasurement of TDs. A Ti: Sapphire laser with awavelength of 700 nm was used as an excitation
source. The laser beam was focused into the interiorof the sample with an objective lens.
Photoluminescence occurs at the focal point in
GaN, and it is extracted from the sample. Only anear-band-edge emission of GaN is corrected byusing a bandpass filter and it is detected with aphotomultipliertube.
Three-dimensional
photoluminescence images are obtained byscanning the focal point of the laser beam in the inplane and depth directions.
The in-plane photoluminescence image
measured at a fixed focal depth showed dark spots,
Keywords: 3D structure, optical properties, defects
Takashi Matsuoka (Physics of Electronic Materials Division)
E-mail: matsuoka@imr.tohoku.ac.jp
URL: http://www.matsuoka-lab.imr.tohoku.ac.jp/?TOPPAGE20

IMR KINKEN Research Highlights 2018

Fig. 1 Three-dimensional photoluminescence image ofGaN. Contrast is inverted: dark lines are shown asbright.

which corresponded to TDs. The diameter of thedark spots was approximately 0.6 µm, which was
determined by the diffusion length of minority
carriers in the sample. The distribution of dark spots
in the in-plane image changed with the focal depth.
The three-dimensional images were constructed bystacking the depth-dependent in-plane images, as
shown in Fig. 1 [1]. All the dark spots connected toform dark lines in the three-dimensional image. This
reflects the propagation behavior of the TDs. By
comparing the TD density, the thickness
dependence of the TD density can be obtained.
The densities of TDs at the depths of 0 µm (surface),
50 µm, and 100 µm were 6.6 × 107, 8.0 × 107, and1.2 × 108 cm−2, respectively. The change in the TD
density showed the annihilation properties of TDs
during the crystal growth.
It can be concluded that this method is powerfulfor characterizing defects in GaN films.
References[1] T. Tanikawa, K. Ohnishi, M. Kanoh, T. Mukai, and T. Matsuoka,
Appl. Phys. Express 11, 031004 (2018).

IMR KINKEN Research Highlights 2018

Toward Constructing Novel Rechargeable Battery Using Mg Cation

We are currently constructing a new type of rechargeable battery using divalent Mg cation as one topic of ourlaboratory. Recently, we have found that Mg insertion into spinel lattices occurs via an “intercalation and pushout” process to form a rocksalt phase in the spinel mother phase. For example, by utilizing the valence change
from Co(III) to Co(II) in MgCo2O4, the Mg insertion occurs at a considerably high potential of approximately 2.9
V vs. Mg2+/Mg, being comparable to the ab initio calculation.

In terms of energy and environmental concerns,
modern industrial society strongly demands highenergy-density rechargeable storage batteries.
Currently, lithium ion batteries (LIBs) are widely used
for many practical applications, and their energy
density has been enlarged year by year, but thisgrowth rate has recently tended to saturate. If lithium
metal itself could be used as an anode material,instead of the currently used carbonaceous materials,
LIBs would have shown significantly high energy
densities. However, this is difficult at present, owing
to the well-known fatal problem, “dendritic growth” ofLi metal on charging that leads to dangerous shortcircuits. Therefore, to further enhance the energy
density of storage batteries, we must develop new
types of metal-anode battery systems.
As an alternative to Li metal-anode batteries,
polyvalent-metal storage batteries have attracted
increased attention owing to their large capacities;
for example, in the case of Mg, its capacity (~2200
mAhg−1) greatly exceeds that of the current
carbonaceous anode materials (~370 mAhg−1). In
particular, Mg electrodeposition tends to occur with
nondendritic formation; therefore, Mg metal can be
expected to work as an anode material. However,Mg rechargeable battery (MRB) research is still avery challenging and unestablished field. Unlesshigh-performance cathode materials are sought
out, MRBs would not be comparable to LIBs in
terms of energy density. Thus, to alter the energy
storage paradigm, we must seek cathode materials
for polyvalent cations.
With several magnesium spinel oxides,
MgCo2O4, MgMn2O4, MgFe2O4, MgCr2O4, andCo3O4, we demonstrated that some of the spineloxides can allow the insertion of Mg cations at highpotentials (~3 V vs. Mg2+/Mg) via an “intercalationand pushout” mechanism in Figs. 1a–1d. Figure 1eshows the results of the cathode performance test[1]. Based on these signifiant results, we are now
trying to construct a new type of dual-carrier battery
using Li and Mg cations [2].

Fig. 1 (a–d) Schematic figure illustrating the insertion
mechanism of Mg cations into the spinel lattice. (e)Discharge test using the MgCo2O4 cathode material.

References[1] S. Okamoto, T. Ichitsubo, T. Kawaguchi, Y. Kumagai, F. Oba,
S. Yagi, K. Shimokawa, N. Goto, T. Doi, and E. Matsubara, Adv.
Sci. 2, 1500072 (2015).
[2] H. Li, T. Ichitsubo, S. Yagi, and E. Matsubara, J. Mater. Chem.
A 5, 3534 (2017).

Keywords: energy storage, oxide, crystal structure
Tetsu Ichitsubo (Structure-Controlled Functional Materials Division)
E-mail: tichi@imr.tohoku.ac.jp
URL: http://ilab.imr.tohoku.ac.jp/index.html

IMR KINKEN Research Highlights 201821

Energy-Related Materials

Effect of the Cooling Rate on the Mechanical Properties of
Ti-Ni-Cu-Zr-Based Glassy/Crystalline Alloys

Ti-Ni-Cu-Zr-based glassy-crystalline dual-phase alloy samples with different sizes and good mechanicalproperties were manufactured. Their deformation curves had a double sigmoidal shape with three deformation
stages. The interplay between dislocation slip and shear deformation of the homogeneous dual-phase structure
contributed the good combination of strength and ductility, in conjunction with the superelastic behavior andthe transformation-induced plasticity effect during martensitic transformation.

The glassy-crystalline dual-phase of bulk
metallic glass composites (BMGCs) emerged at theend of the 20th century to overcome the sudden
fracture of bulk metallic glasses (BMGs) [1]. The
present work investigates the cooling rate effect on
Y-, Co-, and Nb-containing Ti-Ni-Cu-Zr-based
BMGCs. The cooling rate has a significant impact
on the formation of the glassy phase as well as thedeformation behavior via different casting diameters(2 mm, 3 mm, and 5 mm) of cylindrical specimens(length: 50 mm) [2].
Figure 1(a) was taken from the polished crosssectional surface of the as-cast 3-mm diameter
Ti40Ni39.5Cu8Zr10Co2Y0.5 alloy. The alternating
glassy and crystalline phases form the homogeneous
net-like structure.
The mechanical properties are shown in Fig.
1(b). The specimens were deformed to a fairly large
strain of 20% and tolerated a high stress of 2500
MPa prior to fracture. The structures of the Ti-Ni-CuZr based alloys contain a glassy phase with a cP2(Pearson symbol)-type crystalline phase. This cP2TiNi phase coincides with the high-temperature
austenitic phase, which may transform into the lowtemperature martensitic mP4-phase at relatively low
stresses. Furthermore, unlike the serrated plastic
flow typical for BMGs, the massive shear banding
behavior was prevented. Additionally, catastrophic
failure was delayed.
The crystalline phases act as obstacles toshear band propagation and, in conjunction with thesuperelastic and transformation-induced plasticity(TRIP) effects, induce ductility and strength
enhancement. Higher fractions of the mP4 phaseoccur in the larger samples (lower cooling rate) thanin their smaller counterparts. The relatively slow
cooling rate of the large samples promotes
equilibrium-phase formation.
The three stages in the work-hardening curves
correspond to (I) elastic deformation, (II) stressinduced martensitic transformation, and (III) plastic

Fig. 1 (a) SEM images of the polished cross-section of
Ti40Ni39.5Cu8Zr10 Co2Y0.5 alloy. (b) Compressive stress–
strain curves. (c) Curves showing the work-hardening
rate with different diameters.

deformation (Fig. 1(c)). The martensitic transformationis reversible and, hence, the elastic transformationis constrained by the amorphous matrix anddislocation, and shear band propagation is difficult.
Therefore, the martensitic transformation (stage II)
finishes earlier in the 2-mm-diameter sample, whichcontains a larger fraction of the amorphous phase.
The work-hardening rate increases at the plastic
deformation (stage III), and the strain–stress curves
plateau with increasing volume fraction of themartensitic phase.
References[1] C. C. Hays, C. P. Kim, and W. L. Johnson, Phys. Rev. Lett. 84,
2901 (2000).
[2] J. Jiang, S. Ketov, H. Kato, and D. V. Louzguine-Luzgin, Mater.
Sci. Eng. A 704, 147 (2017).

Keywords: bulk metallic glass, deformation, mechanical properties
Hidemi Kato (Non-Equilibrium Materials Division)
E-mail: hikato@imr.tohoku.ac.jp
URL: http://www.nem.imr.tohoku.ac.jp

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IMR KINKEN Research Highlights 2018

Nine Hydrogen Atoms Binding to Transition Metals

Nine-fold hydrogen (H-) coordination is very rare, and has been observed only in two different transition-metal

hydride complexes comprising Group 7 elements, rhenium ([ReH9]2−) and technetium ([TcH9]2−). Here, we
introduce our recent findings in the exploration of novel nine-fold H-coordination hydride complexes.
Despite have the simplest form of any element,
hydrogen has an exceptionally rich chemistry,
forming various chemical bonds in materials. It is
the source of many functionalities in hydrides; thus,
materials containing a large amount of hydrogen
could be promising candidates for the emergenceof latent functionalities [1].
Complex transition-metal hydrides represent aclass of hydrogen-rich materials, wherein a numberof H atoms covalently bind to transition metals toform a varied set of hydride complexes with a richvariety of H-coordination modes. At the same time,nine-fold H-coordination is very rare, and has been
observed only in the Group 7 hydride complexes,[ReH9]2− and [TcH9]2−.
In this regard, by means of a combined
theoretical and experimental approach, we have
explored other nine-fold H-coordination hydridecomplexes. Our density functional theory (DFT)
calculations predicted that a tricapped trigonal
prismatic H-coordination allows the formation ofGroup 5 and 6 hydride complexes of [NbH9]4−/[TaH9]4− and [MoH9]3−/[WH9]3− in Li6NbH11/Li6TaH11
and Li5MoH11/Li5WH11, respectively, as shown in
Fig. 1. The prediction is strongly supported by X-ray
diffraction (XRD) and Raman spectroscopic
measurements of the samples prepared by a highpressure and high-temperature (HPHT) technique[2].
Furthermore, from the results of first-principles
molecular dynamics (FPMD) calculations andneutron diffraction (ND) measurements of thedeuteride analogue, Li5MoD11, we found that thenine-fold H-coordination hydride complexes exhibit
significant rotations at room temperature, as
depicted in the inset of Fig. 2(b). This is strongly
reminiscent of the reorientation jumps of closopolyboranes observed in alkali–metal closopolyborane salts, which are often discussed inrelation to the translational diffusion of alkali metals.
As such, the emergence of fast lithium ion conduction
may be expected in the present materials, even atroom temperature.

Fig. 1 DFT structures of (a) Li6NbH11/Li6TaH11 and (b)Li5MoH11/Li5WH11.

Fig. 2 ND profiles. (a) Experimental profile of Li5MoH11
measured at room temperature. (b) Simulated profile
from FPMD trajectory at 298 K (red line) and Rietveld fitof experimental profile (black line). The inset depicts thetime-averaged atomic-density profile from the FPMD
trajectory of D atoms at 298 K, showing the occurrenceof significant rotations of the hydride complexes.

References[1] S. Takagi and S. Orimo, Scr. Mater. 109, 1 (2015).
[2] S. Takagi, Y. Iijima, T. Sato, H. Saitoh, K. Ikeda, T. Otomo, K.
Miwa, T. Ikeshoji, and S. Orimo, Sci. Rep. 7, 44253 (2017).

Keywords: hydride, first-principles calculations, crystal structure
Shigeyuki Takagi and Shin-ichi Orimo (Hydrogen Functional Materials Division)
E-mail: shigeyuki.takagi@imr.tohoku.ac.jp
URL: http://www.hydrogen.imr.tohoku.ac.jp/index.html

IMR KINKEN Research Highlights 201823

Energy-Related Materials

Growth of Metals and Alloys by the A-μ-PD Method

An innovative method acceptable for the production of iridium (Ir) and ruthenium (Ru) metal fibers with highmelting point and poor workability is developed using an alloy-micro-pulling-down (A-μ-PD) method. Both Ir
and Ru fibers were composed of number of elongated grains oriented along the growth direction, which is
attributable to the unidirectional solidification.

In the case of wire-shaped products, Ir and Iralloy wires have been made from Ir columnar ingots
by multiple hot-working processes using dies withholes of the intended diameter. However, such hotworking processes increase the manufacturing costowing to the yield loss, especially for metals andalloys with difficult workability such as Ir and its
alloys. In addition, the manufacturing cost increases
as a result of losses of starting materials andincreases in labor cost in the working processes.
In this report, Ir and Ru fibers with poor
workability were grown from the melt by the A-μ-PD
method [1]. The key differences between the A-μPD method and traditional μ-PD method areassociated with the crucible design, heating ofstarting materials, and pulling-down system. The
growths were performed from dense-pour ZrO2
crucibles with high mechanical strength and thermal
shock resistance. An Ir fiber exceeding 15 m inlength was grown using a pinch-roller (Fig. 2). The
as-grown Ir and Ru fibers were composed ofelongated grains that demonstrated aligned crystal
orientations along to the growth direction. The
flexibility of the Ir fiber grown by the A-μ-PD method
was considerably improved as compared to acommercial Ir wire made by a wire-drawing process.
This improvement in flexibility is associated with theelongated grains. Therefore, the A-μ-PD method
can be used for improvement in mechanical andchemical properties of the grown fibers, in addition
to the innovative growth of the fibers of metals andalloys with poor workability. Fabrication by the A-μPD method will be applied to the development ofvarious functional metals and alloys in our futurework.
For example, Fe-Ga alloy polycrystals subject
to cross-sectional shape control, such as fiber andplate shape, were successfully grown using the
A-μ-PD method [2]. A prototype vibration energy
harvester showed good performance comparable
to or greater than the device using commerciallyavailable Fe-Ga alloys. Despite the need to improvethe crystal orientation, leveraging the advantages of
Keywords: crystal growth, metal, alloy
Akira Yoshikawa (Advanced Crystal Engineering Laboratory)
E-mail: yoshikawa@imr.tohoku.ac.jp
URL: http://yoshikawa-lab.imr.tohoku.ac.jp/index-e.html

24

IMR KINKEN Research Highlights 2018

Fig. 1 Schematic diagram of the developed A-µ-PD
apparatus.

Fig. 2 Ir fiber grown by the A-μ-PD method and EBSD
image of a cross-sectional plane of the Ir fiber.

the near net-shape controlling and a growth rate
vastly superior to other crystal growth techniques is
expected to underline the role of the shapecontrolled μ-PD method as a promising technique
for the mass-production of Fe-Ga alloys as energy
harvester application materials.
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] M. Ito, K. Kamada, A. Yoshikawa, T. Kawamata, S. Fujieda, S.
Suzuki, T. Minamitani, and T. Ueno, J. Alloys Compd. 731, 898(2018).

IMR KINKEN Research Highlights 2018

Laser Chemical Vapor Deposition of Photocatalytic
Perovskite Films

Photocatalytic NaTaO , SrZrO , and SrTiO perovskite films were prepared by laser chemical vapor deposition
3

3

3(LCVD). The (001) oriented orthorhombic NaTaO3 film showed hydrogen evolution at a rate of 5672 mol g-1 h-1
upon irradiating with a 254-nm UV light. The solar to hydrogen conversion efficiency of the NaTaO3 film is
1.93%, almost three times higher than the previously reported value.

Perovskite-related compounds such as SrTiO3,
SrZrO3, and NaTaO3 are promising photocatalytic
materials for water-splitting under ultraviolet light. In
earlier studies, these films were prepared by wet
chemical route and flux coating. However, it isdifficult to control the orientations and morphologyof these films by wet chemical routes. The
photocatalytic activity is strongly affected by the
crystallinity and crystal orientation of such perovskite
films. A highly crystalline and oriented film is requiredfor high photocatalytic activity. Further, it normallytakes hours to prepare films, which significantly
inhibits the synthesis efficiency. Physical vapor
deposition (PVD) and chemical vapor deposition(CVD) have been widely used to prepare both thinand thick films. However, it is very difficult to control
the composition of alkaline and alkaline-earth
elements, particularly Na composition, in the films
because of the volatility and instability of Na. No
study has so far reported the use of either PVD or
CVD method to prepare NaTaO3 and SrZrO3 films.
Laser CVD is an advantageous method toprepare oxide films as it allows the control of phases,
significant orientations, and morphologies at a very
high deposition rate. The SrTiO3, NaTaO3, and
SrZrO3 films were prepared on polycrystalline AlN
substrates. A continuous wave of Nd:YAG laser(wavelength: 1064 nm) was employed at a laser
output of 10–150 W. The substrate was heated on aheating stage at a pre-heating temperature of 873 K.
The Na(dpm), Sr(dpm)2, Ti(O-i-C3H7)2(dpm)2, andTa(O-i-C3H7)5 were used as precursors. The totalpressure in the CVD chamber was held at 800 Pa.
The deposition process was conducted for 600 s.
Figure 1 shows the surface and cross-sectionalscanning electron microscopy (SEM) images of
NaTaO3 films prepared at Tdep = 793 K (Fig. 1(a) and(c)) and 853 K (Fig. 1(b) and (d)) [1]. The(001)-oriented orthorhombic NaTaO3 film preparedat Tdep = 793 K had a columnar cross-section with atilted roof-like surface. The (100)-oriented monoclinic
NaTaO3 film prepared at Tdep = 853 K had a columnar

(a)

(b)

1 μm

1 μm
(c)

(d)

5 μm

5 μm

Fig. 1 SEM images of NaTaO3 films prepared onpolycrystalline AlN substrates at Tdep = 793 K (a and c)and 853 K (b and d).

cross-section with a plate-like surface. The
photocatalytic hydrogen evolution rate of(001)-NaTaO3 film reached 5672 mol g-1 h-1, which is
6.4 times higher than that of the (112)-oriented
NaTaO3 film and 3 times higher than that of the films
prepared through wet-chemical routes because of
the terraced step structure of the (001)-oriented
NaTaO3 film. The solar to hydrogen conversion
efficiency of the (001) NaTaO3 film was 1.93%.
Highly (121)- and (h21)-oriented SrZrO3 films wereprepared by laser CVD. The hydrogen evolution rateof the SrZrO3 film prepared by laser CVD reached
960 mol g-1 h-1, which is 20 times higher than that of
the film prepared by the solid-state method [2].
References[1] A. M. Huerta-Flores, J. Chen, A. Ito, L. M. Torres-Martínez, E.
Moctezuma, and T. Goto, Mater. Lett. 184, 257 (2016).
[2] A. M. Huerta-Flores, J. Chen, L. M. Torres-Martínez, A. Ito, E.
Moctezuma, and T. Goto, Fuel 197, 174 (2017).

Keywords: photocatalytic, chemical vapor deposition (CVD), hydrogen evolution
Takashi Goto (Multi-Functional Materials Science Division)
E-mail: goto@imr.tohoku.ac.jp
URL: http://www.goto.imr.tohoku.ac.jp/

IMR KINKEN Research Highlights 201825

Electronic Materials

IMR KINKEN Research Highlights 2018

ResearchElectronic Materials

Toward Rare-Earth Spintronics

S

pintronics studies the flow and conversion of the charge and spin of electrons. Rare earths are heavy atoms
characterized by a large spin–orbit interaction that can strongly lock the charge and spin degrees of freedom.
This phenomenon allows the manipulation of rare-earth magnetic moments by electric field gradients, which
occur naturally at the interfaces of gated magnetic-insulator–nonmagnetic-metal heterostructures. A timedependent voltage can induce, for example, magnetization reversal and ferromagnetic resonance.
The exponential growth of computational capacity
yields smaller and denser electric circuits, in whichenergy dissipation becomes increasingly important. To
continue developing more powerful and efficientsystems, we need to envision new mechanisms totransmit, read, and write information with lower energy
losses. The science and technology called spintronics
is pushing these aims by focusing on the coupling,
flow, and conversion of the charge and spin of electrons.
A promising research direction is devoted to thevoltage-induced magnetic dynamics discovered inmagnetic semiconductors [1] and transition metals [2].
We propose to investigate spintronic effects usingheavier atoms, such as rare earths or lanthanides,
which have an extra degree of freedom, namely orbital
momentum, even in the solid state. The orbital
momentum of rare earths is generated by the net
rotation of their inner (4f) electrons and couples to thetotal atomic spin by the strong spin–orbit interaction.
Except when empty, full, or half-filled, 4f shells form anasymmetric charge cloud such as prolate and oblate
ellipsoids oriented along the (principal) symmetry axis
and the electron spin (see Fig. 1). Gadolinium is the
exception, as it is spherical with zero orbital momentum.
Because an electric quadrupole can be manipulated
by electric fields with large gradients, the magnetic
properties that encode the information in computers
can be controlled by pure electric fields as well.
Proceeding from these insights, we theoreticallyanalyzed heterostructures containing rare-earth atoms,
such as dysprosium and holmium, with an emphasis on
the interface of magnetic insulators and nonmagnetic
metals, such as copper [3]. An electric field applied in
the device cannot penetrate in the metal, which implies
that the interface atoms are subject to a nonuniform
field that can re-orient a charge quadrupole. This, via
the spin–orbit-induced spin–charge locking, generates
a torque on the magnetization. We formulate thecoupling between the magnetic moment and theapplied voltage as the electrostatic energy of charged
ellipsoids (the 4f-sub shells), oriented along themagnetization. Our estimates of the coupling strength
find a superior efficiency compared to the known values
Keywords: rare earths, spintronics, voltage
Alejandro León (Theory of Solid State Physics Division)
E-mail: aoleon@imr.tohoku.ac.jp
URL: http://www.bauer-lab.imr.tohoku.ac.jp/

28

IMR KINKEN Research Highlights 2018

Fig. 1 (a) The magnetic subshell of rare earths is elongated(or compressed) along the direction of the orbital
momentum L, which is locked to the spin S. Their
dynamics are therefore rigidly coupled. The curved
arrow illustrates the orbital motion of the 4f electrons.

for transition-metal-based devices [1,2]. Interface
moments are embedded into the magnetization bystrong exchange interactions, such that the interface
torque acts on the total magnetic order. When thevoltage is time-dependent, a plethora of dynamical
responses mediated by interface rare earths, such as
ferromagnetic and parametric resonances, and fast
precessional magnetization switching, can begenerated.
Large deposits of rare earths have been found in
the Japan Exclusive Economic Zone [4], which
represents a unique opportunity for the development ofmany rare-earth-based devices and strong permanent
magnets. We hope that our findings invigorate theresearch for new spintronic effects based on the uniqueproperties of rare-earth-based materials.
References[1] D. Chiba, M. Sawicki, Y. Nishitani, Y. Nakatani, F. Matsukura, and
H. Ohno, Nature 455, 515 (2008).
[2] Y. Shiota, T. Maruyama, T. Nozaki, T. Shinjo, M. Shiraishi, and Y
Suzuki, Appl. Phys. Express. 2, 063001 (2008).
[3] A. O. Leon, A. B. Cahaya, and G. E. W. Bauer, Phys. Rev. Lett. 120,02720 (2018).
[4] Y. Kato, K. Fujinaga, K. Nakamura, Y. Takaya, K. Kitamura, J. Ohta,
R. Toda, T. Nakashima, and H. Iwamori, Nat. Geosci. 4, 535 (2011).

IMR KINKEN Research Highlights 2018

Investigating Successive Phase Transition in LiNiPO4 byPulsed-High-Magnetic-Field Neutron DiffractionS

uccessive magnetic-field-induced phase transition of multiferroic compound LiNiPO4 has been studied byneutron diffraction up to 30 T in pulsed magnetic fields. Alternations of commensurate and incommensurate
magnetic structures are observed in accordance with the appearances of polarizations. Of particular interestis that the polarization appears only in commensurate magnetic phases. Such behavior is significantly different
from conventional multiferric compounds originated from noncollinear magnetic structures. This shows that a
new type of spin–lattice coupling is responsible for multiferroicity in LiNiPO4.
LiNiPO4 has been known as one of the importantbattery-related materials. Moreover, it showsinteresting properties in the magnetic and dielectric
behaviors in high magnetic fields, as shown in Fig.
1(a). The magnetization curve shows several metamagnetic anomalies followed by states with nearlyflat magnetization. The small fraction of themagnetization to the saturation value suggests theexistence of magnetic phases with a long period
modulation. When the dielectric constant ismeasured, it is found that some of the phases areferroelectric. The central question arising from thesebehaviors is: What is the magnetic structure of eachphase and what is the origin of the successive
phase transition?
To determine the magnetic structures inmagnetic fields up to 30 T, we have combined apulsed magnetic field with white pulsed neutron.
The experiment was performed at the SEQUIA
spectrometer in SNS, USA [1]. With the white neutron
beam, we can obtain the Laue diffraction in highmagnetic fields. Figure 1(b) shows the intensity map
along the b-axis, which is indexed by K. The thinlines are the magnetic field traces as functions of K.
Note that the wavevector K or the wavelength of theneutron is related to the time axis of a pulsed
magnetic field through the time-of-flight spectrum of
the white neutron. To scan a particular magnetic
wavevector at a particular magnetic field intensity,
the timing between the pulsed magnetic field andthe pulsed neutron is adjusted. We found a complex
field variation of magnetic wavevectors, as shown in
the graph.
Above 12 T, K = 0.8 appears and it disappears
at approximately 19 T. The K = 1.2 peak is observed
between 16 T and 19 T. There is also intensity at K~1
between 17 and 22 T. Above 22 T, we found a peakat K = 1.33. More precisely, K = 1.2 is commensurate
and others are incommensurate. Such a complex
magnetic field variation of magnetic wave theFig. 1(a) Magenetization curve and the field dependenceof the electric polarization. (b) The intensity map ofneutron scattering along the b*-axis.

neutron Laue method in the pulsed magnetic vector
can be determined only with white neutron Lauediffraction in pulsed magnetic fields. The present
result shows that the interplay among the competingexchange couplings and the magnetic-fielddependent anisotropy of Ni ions are responsible forthe successive phase transition. The contribution of
the field-dependent single ion anisotropy may bringa new mechanism for multiferroics.
References[1] R. Toft-Petersen, E. Fogh, T. Kihara, J. Jensen, K. Fritsch, J.
Lee, G. E. Granroth, M. B. Stone, D. Vaknin, H. Nojiri, and N. B.
Christensen, Phys. Rev. B. 95, 064221 (2017).

Keywords: multi-ferroics, neutron diffraction, high magnetic field
Hiroyuki Nojiri (Magnetism Division)
E-mail: nojiri@imr.tohoku.ac.jp
URL: http://www.hfpm.imr.tohoku.ac.jp/

IMR KINKEN Research Highlights 201829

Electronic Materials

Reconstruction of Spin-Wave Dispersion by Light

We have developed a new method, named spin-wave tomography, to characterize the propagation dynamics
The wave motion of atomic spins in a magnet
serves as an elementary excitation, a so-called spinwave. To know the properties of the spin wave, one
should measure how its frequency changes with its
wavenumber vector. This relation is called thedispersion relation, which represents essential
information of spin waves. Spin waves whose
dispersions are dominated by a dipole–diploe
coupling are called pure-magnetostatic waves.
These are characterized by anisotropic dispersion
relations, representing the anisotropic nature of thedipole–dipole coupling. Although magnetostatic
waves have attracted much attention for theapplication in spintronic and magnonic devices, theobservation of dispersion relations of puremagnetostatic waves has been a challenge.
Recently, we developed a new system for the direct
observation of the dispersion relation of puremagnetostatic waves by a table-top all-optical
spectroscopic method, which we named spin-wave
tomography [1]. Spin waves are excited by theillumination of an ultrashort light pulse focused on
the surface of a magnet. When the duration of thepulse and the excitation area are infinitesimallysmall, the pulse includes all temporal and spatial
wave components according to the Fourier theorem.
Then, spin waves of all frequency and wavenumber
vector can be created and propagate from theexcitation point. The created spin waves aredetected with a time-resolved magneto–opticalimaging system [2]. By Fourier transformation of theobserved spin waves with respect to time andspatial coordinates, we obtain the power spectra of
the spin waves as a function of frequency andwavenumber vector. By the spectra, the dispersion
relation of the spin waves in the pure-magnetostatic
region is determined as clearly demonstrated in Fig.
1. This is the basic concept of spin-wave tomography[1]. Afterwards, we used this method to investigate
the excitation and the propagation dynamics of
optically-excited magnetoelastic waves, which are
the hybridized modes of elastic waves and spinwaves [3]. Moreover, we developed an advanced
procedure of spin-wave tomography, which gives

Frequency [GHz]of spin waves within the long-wavelength regime, which has been difficult with the conventional methods ofspin-wave spectroscopy, with a table-top all-optical method.

1.5
1.0
0.5
0.0

0.0

0.5

1.0
4

-1

1.5

Wavenumber [10 cm ]Fig. 1 Dispersion relation of spin waves observed by spinwave tomography

the phase information of spin waves, and named itphase-resolved spin-wave tomography [4]. The
phase-resolved spin-wave tomography was thenused to investigate the phase of magnetoelastic
waves [5].
References[1] Y. Hashimoto, S. Daimon, R. Iguchi, Y. Oikawa, K. Shen, K.
Sato, D. Bossini, Y. Tabuchi, T. Satoh, B. Hillebrands, G. E. W.
Bauer, T. H. Johansen, A. Kirilyuk, T. Rasing, and E. Saitoh,Nat. Commun. 8, 15859 (2017).
[2] Y. Hashimoto, A. R. Khorsand, M. Savoini, B. Koene, D.
Bossini, A. Tsukamoto, A. Itoh, Y. Ohtsuka, K. Aoshima, A. V.
Kimel, A. Kirilyuk, and T. Rasing, Rev. Sci. Instrum. 85, 063702(2014).
[3] Y. Hashimoto, D. Bossini, T. H. Johansen, E. Saitoh, A. Kirilyuk,
and T. Rasing, Phys. Rev. B 97, 140404 (2018).
[4] Y. Hashimoto, T. H. Johansen, and E. Saitoh, App. Phys. Lett.
112, 072410 (2018).
[5] Y. Hashimoto, T. H. Johansen, and E. Saitoh, Appl. Phys. Lett.
112, 232403 (2018).

Keywords: spin wave, spectroscopy, magnetism
Yusuke Hashimoto1 and Eiji Saitoh1,2,3 (1AIMR, Tohoku Univ., 2Surface and Interface Research Division, IMR, 3 JAEA)
E-mail: yusuke.hashimoto.b8@tohoku.ac.jp
URL: http://saitoh.imr.tohoku.ac.jp/30

IMR KINKEN Research Highlights 2018

IMR KINKEN Research Highlights 2018

Instant lithography by Water Rinse

Modern electronics is based on various types of nanometer-scale devices fabricated by advanced

microfabrication processes. If new materials discovered in laboratories are successfully incorporated into
nanodevices, we will utilize new functionalities of electronic devices. The microfabrication of complex materials,
however, is not straightforward because process damage usually causes a serious deterioration of the physicalproperties of the materials. Developing a device process for each new material requires optimization of theprocess parameters, which often takes much time for a continuous trial-and-error process. Recently, we havedeveloped a versatile microfabrication process using a water-soluble template layer, by which we can pattern
an arbitrary material into a desired shape by rinsing in water.
(a)Target thin ﬁlm growth
Substrate

LaAlO3BaOx(b)

Template

Water rinse

Device(c) 0.5
0.4

SeFe

Rs (kΩ)

New materials have been continuously
discovered in the material science research field,
some of which possess characteristic physicalproperties such as magnetism, ferroelectricity, andsuperconductivity. Making a functional device out ofthe discovered new materials is the next step toward
their application. Material scientists have expended
much effort to develop superior or completely new
functionalities for electronic devices by utilizing avariety of emerging materials.
To develop an electronic device out of a newmaterial, we need to pattern the material into a small
structure, often on the micrometer or even nanometerscale. However, the physical properties of newmaterials are often affected by the formation of
defects and/or distortions during the device
fabrication process. In this study, we developed aversatile damage-free patterning process using awater-soluble template layer, displayed in Fig. 1(a)[1]. First, the LaAlO3/BaOx templates (blue layer) areprepared on oxide substrates by room-temperature
pulsed laser deposition and a standard
photolithography process. Second, the target thinfilms (red layer) are grown at high temperature.
Because of the high melting points of LaAlO3/BaOx,
the device structure of the template layer can be
maintained even in rather extreme conditions, suchas several hundred degrees Celsius under highoxygen pressure. Then, the sample is rinsed inwater using ultrasonic cleaning. As BaOx has highwater solubility, the LaAlO3/BaOx layer is removed
together with the unnecessary part of the target
films. By applying this method, we can patternarbitrary materials into small structures. Different
from the conventional process, severe chemicaltreatment or plasma treatment are not necessary.
We applied the LaAlO3/BaOx process to an ironbased superconductor FeSe (Fig. 1(b)) to fabricate
micron-scale Hall-bar devices.
The FeSe Hall-bar microdevices exhibit identical

0.3

400 µm As-grown

0.2

Patterned

0.1
0

0

100
200
300
Temperature (K)Fig. 1 (a) Process scheme using a LaAlO3/BaOx watersoluble template. (b) Crystal structure of FeSe. (c)Temperature dependence of sheet resistance for thepatterned (red) and pristine (blue) FeSe films. Inset:
optical image of the FeSe Hall-bar.

transport properties with sharp superconducting
transition (black arrow) to those of the pristine films(Fig. 1(c)), indicating essentially no damage during
the process. We have also succeeded in patterninga representative oxide magnet SrRuO3, which
demonstrates the versatility of the patterning
process. We are now exploiting the LaAlO3/BaOx
process to fabricate various types of devices.
Recently, we have discovered an anomalous
behavior of critical current density in ultrathin FeSe
devices [2]. The water-based soft-lithography
process would expand the range of application of
emerging materials in electronic devices.
References[1] T. Harada and A. Tsukazaki, AIP Adv. 7, 085011 (2017).
[2] T. Harada, J. Shiogai, T. Miyakawa, T. Nojima, and A. Tsukazaki,
Supercond. Sci. Technol. 31, 055003 (2018).

Keywords: devices, thin films, oxide
Takayuki Harada (Low Temperature Physics Division)
E-mail: t.harada@imr.tohoku.ac.jp
URL: http://mu.imr.tohoku.ac.jp/

IMR KINKEN Research Highlights 201831

Electronic Materials

Understanding How Itinerant Electrons in Solids Turn to GlassN

ew insights into the behavior of itinerant electrons in an organic crystal as liquids transform to the chargeglass state are deepening our understanding of the universal nature of the liquid-to-glass transition.
Glassy materials are ubiquitous in nature. The
history of glassmaking traces back thousands ofyears and sophisticated glass-forming technology
has been utilized by mankind for centuries. Yet, thefundamental understanding of glassy dynamics
remains one of the most important unresolved
problems in both physics and materials science. We
focus on a unique glassy state of electrons in solids
realized in an organic molecular conductor [1],schematically shown in Fig. 1, where the lack ofperiodicity of the strongly correlated electrons on
the triangular lattice is caused by geometricalfrustration and strong quantum effects.
The quasi-two-dimensional organic compoundθm-(BEDT-TTF)2TlZn(SCN)4 undergoes a chargeordering (CO) transition at Tm ~ 170 K owing tostrong electron correlations, where the charge
carriers on the BEDT-TTF molecules are localized
periodically. Such a CO state can be regarded as a“charge-crystal” state. In contrast, above the COtransition temperature, the charge is distributed
uniformly in space, which is referred to as a “chargeliquid” state. When the sample is cooled faster thana critical cooling rate (~50 K/min), charge
crystallization is kinetically avoided, leading to a“charge-glass” state in which the charges are
randomly quenched.
We quantitatively evaluated the CO volume
fraction from the time evolution of the resistivity
during the charge crystallization process from thesuper-cooled charge-liquid or charge-glass state.
Figure 2 displays a contour map of the CO fraction
plotted in the time–temperature plane, which is a
so-called time–temperature-transformation (TTT)
diagram. The relaxation time becomes faster withdecreasing temperature, and then slower below~160 K, which is referred to as the “nosetemperature”; this characteristic temperaturedependence of the relaxation time can be explainedby the theory of nucleation and growth at a firstorder liquid-crystal phase transition. Our observation
demonstrates that the crystallization process ofelectrons in solids can be described by the
nucleation and growth process of a liquid, as
observed in conventional glass-forming liquids.

Fig. 1 Electrons transition from a liquid state (top) to a
glassy state (bottom) upon cooling.

Fig. 2 TTT diagram of the organic compound θm-(BEDTTTF)2TlZn(SCN)4 derived from the time evolution of theresistivity reflecting the CO volume fraction.

Surprising similarities between our system andconventional glass formers highlight the universal
nature of the liquid–glass transition.
References[1] S. Sasaki, K. Hashimoto, R. Kobayashi, K. Itoh, S. Iguchi, Y.
Nishio, Y. Ikemoto, T. Moriwaki, N. Yoneyama, M. Watanabe, A.
Ueda, H. Mori, K. Kobayashi, R. Kumai, Y. Murakami, J. Müller,
and T. Sasaki, Science 357, 1381 (2017).

Keywords: glass, organic, metal–insulator transition
Kenichiro Hashimoto (Low Temperature Condensed State Physics Division)
E-mail: hashimoto@imr.tohoku.ac.jp
URL: http://cond-phys.imr.tohoku.ac.jp/

32

IMR KINKEN Research Highlights 2018

IMR KINKEN Research Highlights 2018

Charge Density Wave Order Insensitive to Superconductivity
in Electron-Doped High-Tc SuperconductorT

he interplay between charge density wave (CDW) and superconductivity have attracted much attention in the
research of high-Tc superconductivity. We have revealed that in an electron-doped system, the CDW isinsensitive to superconductivity, suggesting a different nature from the CDW order in hole-doped systems.
The high-temperature superconductivity in copperoxides appears with carrier doping into an
antiferromagnetic Mott insulator (Fig. (a)). There are two
types of the superconductors: hole-doped and electrondoped systems, where the carrier charge is positive andnegative, respectively. The electron–hole asymmetry is
one of most important issues for the unified understandingof high-Tc superconductivity. Recent developments insynchrotron X-ray scattering measurements have been
revealing the existence of charge density wave (CDW)
order [1,2]. The detailed nature of the CDW is still underinvestigation, particularly in electron-doped systems,
whereas in the hole-doped systems, it has been
established that the CDW formation is due to an instabilityof the electronic structure at the Fermi surface andcompetes with the superconductivity.
Here, we first performed Cu L3-edge resonant soft
X-ray scattering (RSXS) measurements for representativeelectron-doped high-Tc superconductors Nd2-x Cex CuO4
(NCCO) [3]. Annealed NCCO shows superconductivity,
whereas as-grown (non-annealed) NCCO does not.
Therefore, NCCO is suitable for investigating the relation
between superconductivity and CDW. Figure (c) shows
RSXS scans along the h direction in q = (h, 0) for
superconducting annealed NCCO. A clear peak isobserved at h = 0.26, which is indicative of the putative
CDW order in electron-doped systems [2]. A new findingis that the peak is also observed in nonsuperconducting
as-grown NCCO at the same position. Detailed studies oftemperature, energy, and angle dependencies further
confirm the insensitive nature to superconductivity.
Moreover, to investigate the origin of the peak, wehave carried out angle-resolved photoemission
spectroscopy (ARPES) on the same crystal as used in
RSXS. Figure (e) shows an ARPES spectrum along the ky
direction at (π, 0) of the Fermi surface. The peaks are
positioned definitely off outwardly from ky = 0.26,
corresponding to the wavevector in the RSXS results.
Furthermore, the peak position depends on the annealing
condition. These ARPES results suggest that the
instability of the electronic structure cannot account forthe peak observed in RSXS. These combined results of
RSXS and ARPES call into question the universality of theFig. Phase diagram of (a) annealed and (b) as-grown NCCO asa function of Ce doping. Antiferromagnetic order (AFM)
disappears with Ce doping and the superconductivity (SC)and charge density wave (CDW) appear in the annealed
NCCO. (c)(d) RSXS intensities for annealed and as-grown
NCCO, respectively. The peak indicated by the dashed line
demonstrates the existence of CDW. (e) ARPES spectra alongky at the Fermi surface. The peak positions are definitely off
outwardly from ky = 0.26, which is the RSXS peak position.

CDW in high-Tc superconductivity [3].
References[1] G. Ghiringhelli, M. Le Tacon, M. Minola, S. Blanco-Canosa, C.
Mazzoli, N. B. Brookes, G. M. De Luca, A. Frano, D. G. Hawthorn, F.
He, T. Loew, M. Moretti Sala, D. C. Peets, M. Salluzzo, E. Schierle, R.
Sutarto, G. a. Sawatzky, E. Weschke, B. Keimer, and L. Braicovich,
Science 337, 821 (2012).
[2] E. H. da Silva Neto, R. Comin, F. He, R. Sutarto, Y. Jiang, R. L.
Greene, G. A. Sawatzky, and A. Damascelli, Science 347, 282 (2015).
[3] H. Jang, S. Asano, M. Fujita, M. Hashimoto, D. H. Lu, C. A. Burns, C.
C. Kao, and J. S. Lee, Phys. Rev. X 7, 2 (2017).

Keywords: superconducting, X-ray scattering, electronic structure
Masaki Fujita (Quantum Beam Materials Physics Division)
E-mail: qblab@imr.tohoku.ac.jp
URL: http://qblab.imr.tohoku.ac.jp

IMR KINKEN Research Highlights 201833

Electronic Materials

Magneto–Ionic Control in a Honeycomb-Layer Metal–
Organic Framework Using a Li-Ion Battery SystemMagnetic phase stability was modulated by controlling the radical spin generation/annihilation via electron
doping to a metal–organic framework using a Li-ion battery system. The electron(spin)-inserted state generated
in the discharge process had a higher magnetic phase transition temperature (Tc2 = 33 K) than that of thepristine form (Tc1 < 10 K), which demonstrated reversible phase switching between para- and ferri-magnetic
phases in the range of Tc1 < T < Tc2 by repeating charge/discharge treatments.
In recent years, there has been growing interestin electrical magnetism control based on redoxreactions accompanied by ion transportation; i.e.,magneto–ionic control [1-5]. Magneto–ionic control
achieves an electrochemical equilibrium in amaterial, such that the electrically modulated
magnetic phase should be nonvolatile. This situation
inspires possible applications of functional devices,such as magnetoelectric memory with a low power
consumption.
The Li+-ion battery (LIB) is a representative iontransporting redox system, in which Li+ ions andelectrons simultaneously migrate between twoelectrodes. Hence, we could control the electron
density of the electrode material; e.g., the cathode isfilled with electrons (and Li+ ions) in the discharge
process. Using this concept, we have attempted tocontrol the radical spin generation/annihilation in thebridging ligands of metal–organic frameworks(MOFs) through discharge/charge cycles of a LIB
system [3-5].
As a MOF-cathode, we have focused on a wellknown honeycomb-layer ferrimagnet; (NBu4)[MnIICrIII(Cl2 An)3] (NBu4+ = tetra(n-butyl)ammonium
ion, Cl2 An2– = chloranilate), which underwent
ferrimagnetic ordering at Tc1 < 10 K because of thesuperexchange interaction between Mn2+ (S = 5/2)
and Cr3+ (S = 3/2) via the nonmagnetic bridging
ligand Cl2 An2– (S = 0). Because Cl2 An2– experiences
a reduction to a radical state Cl2 An3•– (S = 1/2), thismaterial was used as a cathode, which could control
the magnetic phase stability tuned by a newly
produced exchange pathway associated withselective electron-filing at the bridging ligand basedon LIB.
The ferrimagnetic phase was indeed stabilized
in the discharged state with an increase in transition
temperature (Tc2 ~33 K). However, in the charged
state, Tc went back to the initial Tc1 state (Fig. 1).
Reflecting the different states between the
discharged and charged states, the reversible

Fig. 1 (a) Schematic figure of magnetism control in MOF
by LIB system. (b) Reversible control of magnetic
phase stability by in situ LIB cell.

magnetic
phaseswitching
betweentheparamagnetic and ferrimagnetic states wasdemonstrated in the temperature range of Tc1 < T <Tc2 [5].
These results could pave the way to theemerging field of magneto–ionics.
References[1] N. Lu et al. Nature. 546, 124 (2017).
[2] U. Bauer et al. Nat. Mat. 14, 174 (2015).
[3] K. Taniguchi, K. Narushima, J. Mahin, W. Kosaka, and H.
Miyasaka, Angew. Chem. Int. Ed. 55, 5238 (2016).
[4] K. Taniguchi, K. Narushima, H. Sagayama, W. Kosaka, N.
Shito, and H. Miyasaka, Adv. Funct. Mater. 27, 1604990 (2017).
[5] K. Taniguchi, J. Chen, Y. Sekine, and H. Miyasaka, Chem.
Mater. 29, 10053 (2017).

Keywords: magnetic properties, molecular devices, electron doping
Kouji Taniguchi and Hitoshi Miyasaka (Solid-State Metal-Complex Chemistry Division)
E-mail: taniguchi@imr.tohoku.ac.jp (K. T.), miyasaka@imr.tohoku.ac.jp (H. M.)
URL: http://www.miyasaka-lab.imr.tohoku.ac.jp/

34

IMR KINKEN Research Highlights 2018

IMR KINKEN Research Highlights 2018

Monolayer-Controlled Co | Ni Epitaxial Superlattices withHigh Magnetic Anisotropy and Low Magnetic DampingH

igh magnetic anisotropy energy (K) and low magnetic damping constant (α) are key properties for materials
of future spintronic devices. Here, we show that monolayer-controlled Co | Ni epitaxial superlattices
simultaneously exhibit higher K and lower α than conventional textured superlattices. Our systematicinvestigation revealed the origin of magnetic anisotropy and magnetic damping for Co | Ni superlattices.
(a)

0

(b)

χ

CoNi 200

50

φ

Au 200
Al2O3 Subs.

40

Qz [nm-1]

Al2O3 Subs.

Au 22030

Al2O3 Subs.

Al2O3 Subs.

2D detector

CoNi 200
20

Diffracted X-ray

Au 20010

0

φ

Al2O3 Subs.

Al2O3 Subs.

Direct BeamSub

te
Incident X-ray

90º
10

20

χ

stra

DirectBeam
0

K

CoNi 111

Au 111

Qxy [nm ]
-1

30

40

Fig. 1 (a) Two-dimensional (2D) diffraction intensity
mapping for x = 1 grown on the Al2O3 (11-20) single
crystal substrate. (b) Cross-section of reciprocal space
for the CoNi 200 and the Au 200 diffractions.
(a)

6

3

K eff (erg/cm )6x10

Epitaxial Co|Ni

4
2
Textured Co|Ni

0

-2
-2
4x10

αeff,min

Magnetic materials with high magnetic
anisotropy (K) and low magnetic damping (α) haveattracted much attention, because both are key
properties to realize a high storage density and low
power consumption for operation in spintronic
devices, and a perpendicularly magnetized Co | Ni
multilayer is one of the promising candidates [1].
The main purpose of this study is to develop Co | Ni
epitaxial superlattices with simultaneously high K
and low α by utilizing a monolayer (ML)-controlled
deposition technique [2].
A molecular beam epitaxy (MBE) system was
employed to grow the ML-controlled Co | Ni
multilayers. The epitaxial Co | Ni superlattices weregrown on an Al2O3 (11-20) single-crystal substratewith V | Au buffer layers and a Au capping layer. The
number of MLs for each Ni layer (x) was varied in
the range from 1 to 4 and the Co layer thickness was
fixed at 1 ML, where 1 ML corresponded to 0.2 nm
for both Co and Ni layers. For comparison, textured
Co | Ni were prepared on a thermally oxidized Si
substrate.
Figure 1(a) displays a two-dimensional (2D)diffraction intensity mapping for x = 1 grown on the
Al2O3 (11-20) single-crystal substrate. We also
constructed the cross-section of reciprocal space
for the CoNi 200 and the Au 200 diffractions (Fig.
1(b)). The six-fold rotational symmetries for both the
CoNi 200 and the Au 200 indicate that the Co | Ni
multilayer was epitaxially grown on the Al2O3 (11-20)
single-crystal substrate with the Au / V buffers.
The effective K (Keff) and effective minimum α(αeff,min) as functions of x are summarized in Figs.
2(a) and 2(b), respectively. For each x, the epitaxial
Co | Ni shows higher Keff and lower αeff,min thanthose for the textured one, resulting in theperpendicular magnetization with low α, even for
the 1 ML-Ni | 1 ML-Co. The first-principles calculation
indicated that the Ni atoms largely contributed to K
for the Co | Ni multilayers. We also found that α wasrelated to the density of states at the Fermi energy.
The present results suggest that the epitaxial Co | Ni

3(b)Textured Co|Ni

2

Epitaxial Co|Ni

1
0
0

1

2

3

4

5

Ni thickness, x (ML)

Fig. 2 (a) Effective K (Keff) and (b) effective minimum α(αeff,min) as functions of x for the epitaxial Co | Ni and the
textured Co | Ni.

superlattice is a promising material to simultaneously
achieve high Ku and low α.
References[1] A. D. Kent, and D. C. Worledge, Nature Nanotech. 10, 187(2015).
[2] T. Seki, J. Shimada, S. Iihama, M. Tsujikawa, T. Koganezawa,
A. Shioda, T. Tashiro, W. Zhou, S. Mizukami, M. Shirai, and K.
Takanashi, J. Phys. Soc. Jpn. 86, 074710 (2017).

Keywords: magnetic properties, molecular beam epitaxy (MBE), spin dynamics
Koki Takanashi (Magnetic Materials Division)
E-mail: koki@imr.tohoku.ac.jp
http://magmatelab.imr.tohoku.ac.jp/

IMR KINKEN Research Highlights 201835

Electronic Materials

Mechanism of Two-Dimensional Nucleation of Colloidal Crystals

Understanding the nucleation and growth mechanism of a colloidal crystal is critical for applying it to novel
functional devices such as photonic crystals. In-situ observations at single-particle resolution enable us tomeasure the steady-state homogeneous two-dimensional nucleation rate and the critical size of nuclei, and therelationship between them and particle concentration is found to agree well with the classical nucleation theory.
The step free energy deduced from the nucleation theory is found to change according to the strength of
attraction between particles.

Because the lattice constant of colloidal crystals
is comparable to the wavelength of visible light, they
are expected to be applied to novel photonic
devices. Particle interactions, such as repulsive,
attractive and hard-sphere, are a significant key
factor for fabricating these novel nanostructured
materials. Attractive interactions have recently been
well utilized. The attractive forces can be used tofabricate a variety of structures that are not obtained
only by repulsive interactions between particles.
However, the growth mechanism of colloidal crystals
with attractive interaction has not been clarified. We
have investigated two-dimensional (2D) nucleationon the terrace of colloidal crystals, in which added
polymers generate a depletion attraction for abalance between colloidal particles [1].
We found that 2D nucleation is the predominant
growth mechanism in the system, where 2D islands
nucleate repeatedly and spread on the surface (Fig.
1(A)). Particles are brought to the terrace from thesolution, diffuse there over a certain length andtime, and then return to solution. When a particle on
the terrace reaches a step, it is incorporated into the
crystal, which advances a step of 2D islands. Someparticles occasionally form clusters, and a nucleus
is formed when those clusters grow. We recognizeda critical size of nucleation, that is, smaller embryos
shrink and then disappear, whereas larger embryos
keep growing. This nucleation process follows theframework of the classical nucleation theory (CNT).
We introduce the area fraction, φarea, as thesurface area concentration of colloidal particles.
The relationship between the nucleation rate, J, andthe critical radius, r*, versus φarea is investigated.
Based on the CNT, J and r*/a are plotted, as in Fig.
1(B) and (C) respectively. The equilibrium volume
fraction, φeq, is measured experimentally as thevalue of φarea at which the growth rate of the steps of
two-dimensional islands is zero. The linear relation
between lnJ and 1/ln(φarea /φeq) indicates that thenucleation behavior is the nucleation process of
Keywords: colloid, crystal growth, nucleation & growth
Jun Nozawa (Crystal Chemistry Division)
E-mail: nozawa@imr.tohoku.ac.jp
URL: http://www.uda-lab.imr.tohoku.ac.jp/index.html

36

IMR KINKEN Research Highlights 2018

Fig. 1 (A) Nucleation and growth of 2D islands observedwith single-particle resolution. (B) lnJ as a function of 1/ln(φarea /φeq). (C) r*/a, as a function of 1/ln(φarea /φeq).

colloidal crystals, which agrees well with the CNT.
We investigated the 2D nucleation of colloidal
crystals on a glass slide [2], which also essentiallyfollows the CNT, and the interfacial energy between
the substrate and crystal is found to play animportant role in the nucleation process.
References[1] J. Nozawa, S. Uda, S. Guo, S. Hu, A. Toyotama, J. Yamanaka,
J. Okada, and H. Koizumi, Langmuir. 33, 3262 (2017).
[2] S. Guo, J. Nozawa, S. Hu, H. Koizumi, J. Okada, and S. Uda,
Langmuir. 33, 10543 (2017).

IMR KINKEN Research Highlights 2018

Field-Tuned Cooper Pairs in Ferromagnetic SuperconductivityT

he coexistence of ferromagnetism and superconductivity attracts much attention, because novel quantum
phenomena based on the novel superconducting mechanism are expected. The field-reentrant or fieldreinforced superconductivity is one of the highlights in unconventional superconductivity. Here, we found that
the Cooper pairs in the ferromagnetic superconductor UCoGe become robust with increasing field when thefield is applied along the hard-magnetization axis. The enigma of ferromagnetic superconductivity was unveiledby means of low-temperaute high-field experiments using high quality single crystals.

20

UCoGe

15
Hc2 (T)

Superconductivity
andmagnetismareantagonistic in the conventional theory ofsuperconductivity. In particular, ferromagnetism isharmful, because the large internal field easily
destroys the superconducting Cooper pairs. The
discovery of ferromagnetic superconductivity in
UGe2, URhGe, and UCoGe introduced a newparadigm for unconventional superconductivity. The
spin-triplet state with equal spin pairing is naturally
expected, because the pair-breaking due to theferromagnetism does not occur. Furthermore, thespectacularfield-reentrant(field-reinforced)
superconductivity was discovered in these threecompounds. The mechanism for this phenomenon
remains unclear.
In order to investigate the field-reinforced
superconductivity, we grew high-quality single
crystals of UCoGe and performed transportmeasurements at very low temperature down to 10
mK and at high field up to 15 T, with fine tuning of
the field direction [1]. Figure 1 shows the temperaturedependence of the upper critical field Hc2 for thefield along the b-axis in the orthorhombic structure
in UCoGe. The Hc2 curve shows the so-called
S-shape, indicating that superconductivity is
abruptly enhanced at high field. As schematicallyshown in Fig. 1, it is found that the strength of the
Cooper pairs, which stabilizes superconductivity, isfield-dependent and becomes large at high field.
Furthermore, it was also demonstrated that the
Ising-type ferromagnetic fluctuations are strongly
enhanced for the field along the b-axis. The
ferromagnetic fluctuations are very sensitive to thefield direction. When the field is applied along theeasy magnetization c-axis instead, the ferromagnetic
fluctuations are immediately suppressed, leading toa small Hc2. The anisotropic field response is incontrast to the case for the A1-phase of 3He, where
the electrons with only one direction are paired.
This work was done in collaboration with G.
Knebel, A. Pourret, B. Wu, G. Bastien, M. Taupin, C.

10 Superconductivity
5
0
0

0.2
0.4
Temperature (K)0.6

Fig. 1 Temperature dependence of the upper critical field
Hc2 for H // b-axis in the ferromagnetic superconductor
UCoGe. The strength of superconducting Cooper pairs
increases with the field.

Paulsen, L. Howald, J. P. Brison, and J. Flouquet in
CEA-Grenoble.
References[1] B. Wu, G. Bastien, M. Taupin, C. Paulsen, L. Howald, D. Aoki,
and J. P. Brison, Nat. Commun. 8, 14480 (2017).

Keywords: superconducting, heavy fermion
Dai Aoki (Actinide Materials Science Division)
E-mail: aoki@imr.tohoku.ac.jp
http://actinide.imr.tohoku.ac.jp/

IMR KINKEN Research Highlights 201837

Electronic Materials

Low-Temperature Deposition of Piezo-Films Using
Hydrothermal Method

Flexible piezo-films have been widely investigated in a variety of applications. To fabricate such films, it isKNbO3{001}
KNbO3{002}
240°C
150°C
120°C
SrRuO3//SrTiO3 sub.

20

30

40

50

2θ, CuKα1 (deg.)

Fig. 1 XRD 2θ – ω profiles of films deposited at various
temperature.
● KNbO3● ▲ K3Nb7O19●

Log[Intensity (arb. unit)]

KNbO3 films, which is one of the piezo-films
with a perovskite structure, were deposited on (100)c SrRuO3//(100)SrTiO3 substrates as well as KNbO3
powders for 6 h by a hydrothermal method. The raw
materials were Nb2O5 powder and KOH solution.
These source materials and substrates were sealed
in an autoclave, which was set in a thermostat bathmaintained at a fixed temperature. After preparation,
the KNbO3 films and powders were ultrasonicallywashed, and then dried under the deposition
temperature in air.
Figure 1 shows XRD 2θ – ω profiles of films
deposited at various temperatures. All XRD profiles
showed only {001}c diffraction peaks of theperovskite structure. In addition, these films were
epitaxially grown on substrates. Therefore,{001}-oriented epitaxial KNbO3 films were obtainedeven at a low temperature of 120 °C. Figure 2 shows
XRD 2θ – ω profiles of powders prepared
simultaneously in the same batch shown in Fig. 1. In
the case of 240 °C deposition, only KNbO3 powder
was obtained. However, the diffraction peaks arisingfrom the secondary phase, such as Nb2O5 andK3Nb7O19, were observed with decreasing
deposition temperature. This means that it is difficult
to obtain KNbO3 powders at a synthesis temperature
lower than 150 °C.
From above results, it is considered that KNbO3
films can be obtained even at a low temperature of
120 °C, because the SrRuO3 layer with a perovskite
structureaccelerated
theinhomogeneous
nucleation. In fact, the homogeneous nucleation of
the perovskite structure has not been achieved atsuch a low temperature. Therefore, it was found thatthe design of the surface layer of a substrate is a key
to obtaining piezo-films at a low temperature by ahydrothermal method. Using this technique, it ispossible to fabricate flexible piezo-films. [1,2]Log[Intensity (arb. unit)]

essential to deposit piezo-films on organic substrates. Normally, the heatproof temperature of organic substrates
is less than 200 °C, whereas most of the deposition methods require temperatures higher than 500 °C to form
piezo-films. Therefore, it is difficult to realize flexible piezo-films. In this study, the possibility of low-temperaturedeposition of piezo-films using a hydrothermal method was investigated.

240°C
●

●

150°C

●

●

●
●

20

120°C

▲

▲

Nb2O5

30

40

2θ, CuKα1 (deg.)50

Fig. 2 XRD 2θ – ω profiles of powders simultaneously
synthesized with KNbO3 films.

References[1] T. Shiraishi, N. Kaneko, M. Ishikawa, M. Kurosawa, H. Uchida,and H. Funakubo, Jpn. J. Appl. Phys. 53, 09PA10 (2014).
[2] T. Shiraishi, M. Ishikawa, H. Uchida, T. Kiguchi, M. K.
Kurosawa, H. Funakubo, and T. J. Konno, Jpn. J. Appl. Phys.
56, 10PF04 (2017).

Keywords: hydrothermal, piezoelectric, thin films
Takahisa Shiraishi (Materials Science of Non-Stoichiometric Compounds Division)
E-mail: takahisa.shiraishi@imr.tohoku.ac.jp
URL: http://konno-lab.imr.tohoku.ac.jp/index.html

38

IMR KINKEN Research Highlights 2018

IMR KINKEN Research Highlights 2018

Different Photoisomerization Routes in the Structural
Isomers of Cinnamate-Based SunscreensThe Professional development Consortium for Computational Materials Scientists (PCoMS) supports young
researchers in computational materials science to develop their broader view and extensive knowledge ofinterdisciplinary areas among materials science, condensed matter physics, molecular science, and materials
design. Introduced bellow is a recent study by one of the key members of PCoMS. Prof. Yamazaki and coauthors
both theoretically and experimentally found that the photoisomerization pathways of cinnamate-based
sunscreens depend on their substitution positions.
Cinnamate derivatives are widely usedmolecules in nature and industry, as the chromophoreof photo-active yellow protein, sunscreens of many
plants to protect their DNA, UV absorber ofsunscreen cosmetics, etc. Understanding thenonradiative decay (NRD) mechanisms should
enable the realization of new effective sunscreensand other photofunctional materials. In this study,
we investigated the NRD pathways of jet-cooled
para-methoxy methylcinnamate (p-MMC) and paramethoxy ethylcinnamate (p-MEC), ortho-, meta-,
and para-hydroxy methylcinnamate (o-, m-, andp-HMC, respectively) by picosecond andnanosecond pump-probe spectroscopy, and lowtemperature matrix-isolation Fourier Transform
Infrared Spectroscopy (FTIR) spectroscopy. The
possible NRD pathways were calculated by thesingle-component artificial force induced reaction(SC-AFIR) method combined with the timedependent density functional theory.
We found that the all investigated cinnamatebased sunscreens undergo trans → cis photoisomerization under UV irradiation, but differ in theisomerization pathway. p-MMC, p-MEC, andp-HMC are isomerized via multistep intersystemcrossing (ISC) from the bright 1ππ* state to the 3ππ*state, mostly via stepwise ISC followed by theinternal conversion (IC) from 1ππ* to the dark 1nπ*state (Fig. 1) [1,2].
However, m- and o-HMC are directly isomerizedby twisting along the C=C double bond to 90° on
the S1 state and subsequent IC to the electronic
ground (S0) state (Fig. 2) [2]. These results suggestthat controlling the substitution position is essential
for designing the cinnamate-based photofunctional
materials.

Fig. 1 Multistep intersystem crossing (ISC) pathway of
p-MMC, which is followed by the internal conversion(IC) from 1ππ* to the dark 1nπ* state.

Fig. 2. Schematic of the photo-isomerization pathway of
HMC-based sunscreens with different substitution
positions [2]. p-HMC are isomerized via multistep
intersystem crossing (ISC) from the bright 1ππ* state to
the 3ππ* state. In contrast, m- and o-HMC are directlyisomerized by twisting along the C=C double bond to
90° on the S1 state and subsequent IC to the S0 state.
Maeda, Y. Inokuchi, S. Kinoshita, M. Sumida, Y. Onitsuka, H.
Kohguchi, M. Ehara, and T. Ebata, J. Phys. Chem. Lett. 7, 4001
(2016).
[2] S. Kinoshita, Y. Miyazaki, M. Sumida, Y. Onitsuka, H. Kohguchi,
Y. Inokuchi, N. Akai, T. Shiraogawa, M. Ehara, K. Yamazaki, Y.
Harabuchi, S. Maeda, T. Taketsugu, and T. Ebata, Phys. Chem.

References

Chem. Phys., DOI: 10.1039/C8CP00414E (2018) in press[1] K. Yamazaki, Y. Miyazaki, Y. Harabuchi, T. Taketsugu, S.

(Featured on the back cover).

Keywords: organic, first-principles calculations, electronic structure
Kaoru Yamazaki (Professional development Consortium for Computational Materials Scientists)
E-mail: kaoru.yamazaki@imr.tohoku.ac.jp
Tetsuo Mohri (Project Leader of Professional development Consortium for Computational Materials Scientists)
URL: http://pcoms.imr.tohoku.ac.jp/index.html

IMR KINKEN Research Highlights 201839

Research Centers

IMR KINKEN Research Highlights 2018

ResearchResearch Centers

Novel STEM Imaging of Dislocation Loops in Steels
International Research Center for Nuclear Materials ScienceT

he size distribution and number density of small dislocation loops are some of the most important structuralparameters for characterizing the hardening of steel/metallic alloy. In transmission electron microscopy (TEM),
an accurate quantification of such nanoscaled defects heterogeneously dispersing in the matrix has been asignificant challenge for over 60 years, because of strong interference artifacts due to the parallel wave of TEM.
The convergent electron wave and dedicated scanning system of weak-beam scanning TEM are highlighted
as a solution for radiation damage.
To achieve more accurate quantification oflattice defects in steels and metallic alloy samples,anadvancedspherical-aberration-correctedtransmission electron microscope in the Oarai
center was innovatively modified in 2016. The
design of a new optics system for the diffraction
contrast imaging of dislocation loops was named as
weak-beam scanning transmission electron
microscopy (WB-STEM). By installing a novel beam
selector, Howie’s detector, a high-speed CCD
camera, and imaging filter in a camera chamber ofan aberration-corrected electron microscope,nonlinear contrast imaging consisting of WB-STEM
imaging and 3D electron tomography were achievedin addition to conventional elemental analyses, suchas STEM-Energy dispersive X-ray spectrometry(EDS) and STEM-electron energy loss spectroscopy(EELS) (Fig. 1(a)).
The capabilities of the WB-STEM were firstly
applied to neutron-induced lattice defects in reactor
pressure vessel (RPV) steels. Systematic WB-STEM
analyses of size distribution and number density of
dislocation loops in each RPV steel with neutron
fluences of 1.3 × 1023, 3.4 × 1023, 8.2 × 1023, and1.2 × 1024 n m−2 with a flux of 1.3 × 1015 n m−2 s−1
are finally achieved and correlated with chemical
analysis by atom probe tomography and the point
defects quantification using positron annihilation
spectroscopy.
The development of the WB-STEM and its
application to RPV steel have been applauded in
the journal Microscopy as a key technology forvisualizing lattice defects (Fig. 1(b)) [1]. In 2017, the
WB-STEM contributed to two Ph.D theses and 10+
research projects from home and abroad as acommon facility in the Oarai center.

(a)

(b)

Fig. 1 (a) Schematic of the WB-STEM, which consists of asmall probe aperture, wide-gap pole piece, two-hole
BF aperture, annular detector and CCD camera. (b)
WB-STEM image of RPV steel with (g, 3g), g = 1−10.
The arrows and ellipse indicate small dislocation loops
and loops that lie on a dislocation, respectively.

References[1] K. Yoshida, M. Shimodaira, T. Toyama, Y. Shimizu, K. Inoue, T.
Yoshiie, K. J. Milan, R. Gerard, and Y. Nagai, Microsc. 66, 120(2017).

Kenta Yoshida (Corresponding Author, International Research Center for Nuclear Materials Science)
E-mail: k_yoshida@imr.tohoku.ac.jp
Yasuyoshi Nagai (Head of International Research Center for Nuclear Materials Science)
E-mail: nagai@imr.tohoku.ac.jp
URL: http://www.imr-oarai.jp/

42

IMR KINKEN Research Highlights 2018

IMR KINKEN Research Highlights 2018

Switching of Magnetic Ordering in Uranium Intermetallic
Compound U(Ir1−xRhx)GeInternational Research Center for Nuclear Materials ScienceThe evolution of magnetic ordering in intermetallic uranium compounds is studied. An antiferromagnetic
ground state of UIrGe is shown to suddenly transformed to a ferromagnetic one by the substitution of Ir by Rh.
The resulting density of states is highly different in the ferromagnetic and antiferromagnetic ground states.

Fig. 1 Magnetic transition temperature of U(Rh,Ir)Ge andU(Co,Rh)Ge alloys. The horizontal axis is the interatomic
distance between neighboring uranium atoms [4].

γUranium intermetallic compounds with an
orthorhombic TiNiSi-type crystal structure are
attracting attention because two of the compounds
belonging to this family, UCoGe and URhGe, are
known as ferromagnetic superconductors. On thecontrary, isostructural and isoelectronic UIrGe is an
antiferromagnet without superconductivity down to
50 mK, even for an extremely high-quality single
crystal [1]. It is suggested that ferromagnetism inthese compounds is essential for realizing
superconductivity. But how can the ferromagnetic
ordering be stabilized in these compounds?
We studied the evolution of magnetic groundstates this system by substituting transition metalsites [2]. In UTGe (T = Co, Rh, and Ir), magnetism isdominated by the uranium 5f electrons. Transition
metals are almost magnetically inert. It is therefore
expected that the substitution of the transition metalsites would exert chemical pressure. Figure 1 shows
the magnetic phase diagram in the U(Ir1−x Rhx)Ge
alloy. For comparison, the result for U(Co1-x Rhx)Ge[3] is also shown. The transition temperatures areplotted as a function of the interatomic distance ofneighboring uranium atoms dU–U [4]. Although dU–U
changes only gradually, the magnetic transition
temperature changes drastically upon substitution.
More interestingly, the antiferromagnetic (AFM)
ground state of UIrGe switches to a ferromagnetic(FM) state suddenly at the critical composition
U(Ir0.44Rh0.56)Ge. Precise experiments near thecritical composition have shown that the AFM/FMtransition is of the first order. This result demonstrates
that a slight modification of dU–U can even change
the magnetic structure. Fig. 2 shows a plot of theelectronic specific heat coefficient γ in the orderedstate. γ in the FM phase is almost independent of thesubstitution showing values as large as typicalheavy fermion materials. In AFM, however, γ issignificantly reduced. This suggests that the AFM
ordering exhausts the majority of electronic entropy,
leaving a relatively low electronic density of states at

Fig. 2 Electronic specific heat coefficient of U(Rh,Ir)Ge.

the Fermi energy.
This demonstrates that the FM and AFM states
are equally stable in this system, but the resulting
ground state density of states is significantly
different. The results suggest the importance of ahighly enhanced density of states in the FM groundstate for superconductivity in UCoGe and URhGe.
References[1] J. Pospíšil, J. Gouchi, Y. Haga, F. Honda, Y. Uwatoko, N.
Tateiwa, S. Kambe, S. Nagasaki, Y. Homma, and E. Yamamoto,J. Phys. Soc. Jpn. 86, 044709 (2017).
[2] J. Pospíšil, Y. Haga, S. Kambe, Y. Tokunaga, N. Tateiwa, D.
Aoki, F. Honda, A. Nakamura, Y. Homma, E. Yamamoto, and T.
Yamamura, Phys. Rev. B 95, 155138 (2017).
[3] N. Huy and A. de Visser, Solid State Commun. 149, 703 (2009).
[4] D. Aoki and J. Flouquet, J. Phys. Soc. Jpn. 81, 011003 (2012).

Yoshinori Haga (Corresponding Author, Advanced Science Research Center, JAEA)
E-mail: haga.yoshinori@jaea.go.jp
Yasuyoshi Nagai (Head of International Research Center for Nuclear Materials Science)
E-mail: nagai@imr.tohoku.ac.jp
URL: http://www.imr-oarai.jp/

IMR KINKEN Research Highlights 201843

Research Centers

High-Performance Ni3(Al, V) L12 Intermetallic-Based Alloys
as High-Temperature Structural Materials
Cooperative Research and Development Center for Advanced Materials

T

he Center contributes to research and development of new materials and their fabrication processes in order
to explore the possibility of their application as multifunctional materials for future technology under collaboration
with universities and government organizations. Here, we highlight our recent activity of investigating themechanical properties of the novel Ni3(Al,V) L12 intermetallic-based alloys in the field of high-temperature
structural materials.
1000
900

Nominal Strain, σ [MPa]The center has developed novel materials andprocesses under collaboration with universities andgovernment organizations. One of these is theresearch on Ni3(Al,V) L12 intermetallic-based alloys,
which have been investigated by our center andOsaka Prefecture University [1-4].
The Ni3(Al,V) alloys, which have a single phase ofordered L12 cubic structure with a composition of Ni13 at.% Al-12 at.% V, are fabricated by solutiontreatment at a high temperature of 1050 °C and thenquenched in water. The Ni3(Al,V) alloys exhibit superiormechanical strength and ductility at high temperatures(Fig. 1). The fractural elongation of the alloys exceeded
20% at room temperature and above 5% even at 800°C, which is considerably superior to conventional
Ni3Al intermetallic alloys. Additionally, the yieldstrength of the Ni3(Al,V) alloys increases withincreasing temperature (referred to as “the anomalous
temperature dependency of yielding”), which isdesirable property for high-temperature applications.
It was also found that both the strength andductility of the Ni3(Al,V) alloys can be further
improved by aging after quenching, which is causedby an age-induced precipitation hardening effect.
Figure 2 shows a TEM image of the Ni3(Al,V) alloys
aged isothermally at 850 °C. A number of fineprecipitates of Ni3V D022 (tetragonal structure, a =0.381 nm, c = 0.592 nm) were formed coherently onthe {001} planes of the Ni3(Al,V) L12 (cubic, a = 0.373nm) matrix. The number and size of the plateshaped Ni3V precipitates increased gradually withincreasing aging time.
Thus, a proper design of the alloy composition
and thermomechanical process for the Ni3(Al,V)
alloys are required to enhance their mechanicalstrength and ductility at an elevated temperature.
The detailed findings to control the microstructure
and mechanical properties will be reported in thenear future.

800

400oC

Room
temp.

600oC

700

700oC

600

800oC

500
400
300
200
100
0

10%
Nominal strain, εFig. 1 Tensile stress–strain curves for the Ni3(Al,V) alloy
from room temperature to 800 °C. The 0.2% yield stressis marked by arrows.

Fig. 2 Bright-field TEM images and selected-area electron
diffraction patterns taken from the matrix and precipitatesin the Ni3(Al,V) alloy aged at 850 °C for 48 h.

References[1] D. Edatsugi, Y. Kaneno, S. Semboshi, and T. Takasugi, Metall.
Mater. Trans. A. 47, 998 (2016).
[2] S. Semboshi, H. Tsuda, Y. Kanano, A. Iwase, and T. Takasugi,
Intermetallics. 59, 1 (2015).
[3] R. Sasaki, S. Semboshi, M. Nagasako, Y. Kaneno, A. Iwase, andT. Takasugi, 2016 MRS Fall Meeting, Boston, USA, 2016.
[4] R. Sasaki, Master‘s thesis in Osaka Pref. Univ. (2017).

Satoshi Semboshi (Corresponding Author, Cooperative Research and Development Center for Advanced Materials)
E-mail: semboshi@imr.tohoku.ac.jp
Tadashi Furuhara (Head of Cooperative Research and Development Center for Advanced Materials)
E-mail: crdam@imr.tohoku.ac.jp
URL: http://www.crdam.imr.tohoku.ac.jp/ja/index.html

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IMR KINKEN Research Highlights 2018

Robust Emergent-Monopole Fluctuations as a Source of
Large Thermoelectric Conversion
High Field Laboratory for Superconducting Materials

Hairy magnetic structures with nontrivial topology, so-called spin hedgehogs, behave as emergent monopoles,
which affect the motion of conduction electrons in various ways. By exploiting steady magnetic fields of a 25 T
cryogen-free superconducting magnet, we have identified that robust fluctuations of emergent monopoles playa key role in the large thermoelectric effect persisting up to high magnetic fields in a chiral magnet MnGe.
Complex electronic orders are a fertile sourceof emergent electromagnetic responses, the origins
of which depend on the geometry of the assembled
constituents and their collective behavior. Relevant
examples include a variety of topological spin
textures, such as solitons, skyrmions, andhedgehogs; they exhibit rich transport andmagnetoelectric properties via transcribing thegeometry of each spin ensemble to the electronic
states [1]. In particular, the unique three-dimensional
spin arrangement of hedgehogs produces aquantized source and sink of an effective gauge
field, that is, emergent monopoles (Fig. 1(a)).
Because of their fluctuations and consequentconsiderable dynamical variation in the emergent
magnetic field distribution, the charge carriers get
scattered, acquiring large entropy.
Here, we experimentally identify the origin of an
unusually enhanced thermopower by the applicationof magnetic field in MnGe with a spin-hedgehog
lattice as the emergent monopoles’ fluctuations [2].
Throughhigh-fieldmeasurementsofthethermoelectric effect (Seebeck effect) in the 25 T
cryogen-free superconducting magnet (25 T-CSM)
installed at IMR, Tohoku University, we revealed that
their strong fluctuations—the source of large entropy
and thus thermopower—can remain at high magnetic
fields above 10 K, and eventually quenched below
5 K (Fig. 1(b)).
The observed robustness is possibly rooted in
topological protection against unwinding of the spin
texture by external magnetic fields; this property
could be captured only by utilizing the steady highmagnetic fields of the 25 T-CSM. The present results
not only open the door to efficient thermoelectric
conversion in topological magnets, but also
demonstrate the promising usefulness of high-fieldmeasurements to clarify the topological stability ofspin nano-objects.

Fig. 1 (a) Spin hedgehogs and corresponding emergent
field distributions (emergent monopoles). (b) Magnetic
field dependence of thermopower at 2, 5, and 10 K.

References[1] N. Kanazawa, S. Seki, and Y. Tokura, Adv. Mater. 29, 1603227(2017).
[2] Y. Fujishiro, N. Kanazawa, T. Shimojima, A. Nakamura, K.
Ishizaka, T. Koretsune, R. Arita, A. Miyake, H. Mitamura, K.
Akiba, M. Tokunaga, J. Shiogai, S. Kimura, S. Awaji, A.
Tsukazaki, A. Kikkawa, Y. Taguchi, and Y. Tokura, Nat.
Commun. 9, 408 (2018).

Naoya Kanazawa (Corresponding Author, Department of Applied Physics, School of Engineering, The University of Tokyo)
E-mail: kanazawa@ap.t.u-tokyo.ac.jp
Hiroyuki Nojiri (Head of High Field Laboratory for Superconducting Materials)
E-mail: nojiri@imr.tohoku.ac.jp
URL: http://www.hflsm.imr.tohoku.ac.jp/

IMR KINKEN Research Highlights 201845

Research Centers

Scientific Breakthrough Toward Creation of New Industrial Materials
Trans-Regional Corporation Center for Industrial Materials ResearchInstitute for Materials Research (IMR) has launched the Trans-Reginal Corporation Center, a comprehensive
Institute-wide effort that pairs IMR’s research groups across the innovation spectrum to solve today’s industrial
challenges and transform tomorrow’s global energy problems. The center was established in April 2016 basedon an agreement between IMR, the Osaka Prefecture Government, and enterprises in the Kansai areasponsored by government, taking over Osaka and Kansai center projects.
The Trans-Reginal Corporation Center was
established in Osaka as a special unit in 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 government(Ministry of Education, Culture, Sports, Science andTechnology) and took over the Kansai Center, which
carried out its mission from 2012 to 2016. The TransReginal Corporation Center has three missions. First, tosolve technical problems that industrial stakeholders havestruggled to resolve. Second, the center introduces
academic output to industries, with the aim of applying
such output to society. Third, the center helps to educate
next-generation materials scientists and researchers inuniversities and enterprises. We have organized abimonthly forum named “Monodukuri Kisokoza,” which
focuses on special topics regarding materials andprocessing. Projects are conducted through wide
collaborations between the government, universities,
research institutions, and other organizations. The centerhas four venues to cover the Kansai area: the Osaka
office at Osaka Prefecture University, the Hyogo office at
the University of Hyogo, the Sendai office in IMR, and the
Monozukuri Business Information Center Osaka (MOBIO)in the Creation Core Higashi-Osaka, a governmental bodyin which fifteen local universities and one college arelocated to facilitate collaboration with various industries.
The center has developed materials and processes
under collaboration with industries, universities, andgovernment organizations. One of these is a consolidation
process of metallic glass powders, which has beendeveloped by IMR and Porite Co., LTD under the strategic
core technology advancement program of Ministry of
Economy, Trade and Industry (METI). The Ni-Cr-Nb-P-B
metallic glasses (Ni-MGs) exhibit high glass forming
ability, high yield strength, and high corrosion resistance.
No crystalline particles were observed in the gas atomized
Ni-MG powders with diameter below 53 μm, even with theuse of low-grade raw material. In order that back extrusion
and high heating rate consolidation process applies large

Fig. 1 (a) Automatic and high-rates consolidation system
for MGs, (b) the extruded sample of Ni-MG, (c) the trial
components of miniature bearing (O.D. = 6.35 mm, I.D.
= 3.175 mm) with Ni-MG. The inner and outer bearing
races are manufactured by the consolidation process of
Ni-MG powders.

shearing to powder with low viscosity, the Ni-MGs indicate
good consolidation. Furthermore, the automatic and highrates powder consolidation system for MGs with novacuum was also developed [Fig. 1(a)], and can carry out
consolidation of 60 parts per hour of Ni-MG. A miniature
bearing with Ni-MG [1] was demonstrated as the results ofdevelopment [Fig. 1 (b, c)].
Similar collaboration research studies for practicalapplications utilizing academic knowledge and industrial
technology are in progress. The Trans-Reginal Corporation
Center will endeavor to innovate in the metallic material
industry through the alliance with partners in the Kansaiarea, and promote research of materials science.
References[1] F. Habuki, Y. Saotome, K. Amiya, N. Shimada, A. Okuma, T. Iwasaki,
and H. Kimura, Japan Patent Publication number 2017-122510, Dateof filing 2017-7-13.

Kenji Amiya (Corresponding Author, Trans-Regional Corporation Center for Industrial Materials Research)
E-mail: amiya.k@imr.tohoku.ac.jp
Naoya Masahashi (Head of Trans-Regional Corporation Center for Industrial Materials Research)
E-mail: masahasi@imr.tohoku.ac.jp
URL: http://www.trc-center.imr.tohoku.ac.jp/

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IMR KINKEN Research Highlights 2018

Supercomputing to Understand Materials Properties
Center for Computational Materials ScienceT

he Center for Computational Materials Science supports various advanced studies on computational
materials science by providing users with an efficiently tuned high-performance computer. We introduce two
major activities selected from approximately 120 users. Dr. Tsukahara and Dr. Ono investigate the properties ofisotropic nanocrystalline permanent magnets. Dr. Takahashi investigates the terahertz-spectral property of
nicotinamide, focusing on the temperature.

Temperature Dependence in the Terahertz
Spectrum of Nicotinamide: Anharmonicity andHydrogen-Bonded Network b)
By analyzing the terahertz (THz) spectrum of
nicotinamide with dispersion-corrected density
functional theory calculations, we recently found thatthe difference in the temperature-dependent peak shift
is well understood in terms of the presence/absence ofstretching vibration of the intermolecular hydrogenbond (Fig. 2) in the mode and the change in cellparameters [2]. Almost all peaks in the THz spectrum
showed a remarkable peak shift with temperature,
whereas the lowest-frequency peak showed a negligible
shift. The anharmonicity in the dissociation potential
energy of very weak intermolecular hydrogen bonds
causes the remarkable peak shift. The stationary
feature of the lowest-frequency peak is explained by
combining two effects, that giving the opposite

1

(a)

16 nm

512 nm0.5-0.5

Hc (units of 2K1u/Ms)

16

(b)

0

mz

Magnetization Reversal Processes of Isotropic
Permanent Magnets with Various Intergrain
Exchange Interactions a)
A permanent magnet is a key material for highefficiency power motors, which are essential forelectric vehicles. However, the coercivity of realmagnets is much smaller than the theoretical value.
We performed large-scale micromagnetic simulations
to reveal the discrepancy between the actual andtheoretical coercivity using a simple simulation model,
as shown in Fig. 1(a). Figure 1(b) shows the coercivityof the simulation models as a function of the intergrainexchange interaction parallel and perpendicular to theexternal field [1]. When the intergrain exchangeinteraction acts only parallel to the external field (typeA), the degradation of the coercivity is the smallest. In
contrast, the coercivities are strongly degraded withincreasing the intergrain exchange interaction parallelto the external field (type B) and all directions (type O).

nm

16

512

nm

2
51

nm

nm z y

-1

x

0.5
0.4
0.3

Type A
Type B
Type O

0.2
0.1
0
0

0.2

0.4

ξ

0.6

0.8

1

Fig. 1 (a) Schematic of the isotropic nanocrystalline
permanent magnet model. (b) Coercive force Hc as afunction of the strength of the intergrain exchangeinteraction ξ.

Fig. 2 Calculated vibrational modes with intermolecular
weak hydrogen-bond stretches.

frequency shift to low frequency due to the volume
expansion and that to high frequency due to theintermolecular or interatomic repulsions.
References[1] H. Tsukahara, K. Iwano, C. Mitsumata, T. Ishikawa, and K. Ono,
AIP Adv. 7, 056224 (2017).
[2] M. Takahashi, N. Okamura, X. Fan, H. Shirakawa, and H.
Minamide, J. Phys. Chem. A 121, 2558 (2017).

a) Hiroshi Tsukahara (Corresponding Author, High Energy Accelerator Research Organization) and Kanta Ono (High
Energy Accelerator Research Organization)
E-mail: thiroshi@post.kek.jpb) Masae Takahashi (Corresponding Author, Graduate School of Agricultural Science, Tohoku University)
E-mail: masae@fris.tohoku.ac.jp
Momoji Kubo (Head of Center for Computational Materials Science)
URL: http://www.ccms.imr.tohoku.ac.jp/Eng/IMR KINKEN Research Highlights 201847

Research Centers

Interaction of Grain Boundaries at Crystal/Melt Interface of Silicon
Collaborative Research Center on Energy Materials

What will happen when two grain boundaries meet at a crystal/melt interface? To answer this question, we
directly observe the crystal/melt interface of multicrystalline silicon during directional solidification.

Multicrystalline silicon (mc-Si) grown throughdirectional solidification is the dominant material inphotovoltaic applications. A grain boundary (GB) in
mc-Si is one of the most significant factors
deteriorating the conversion efficiency of solar cells.
However, the behaviors of GBs at a crystal/meltinterface have not been well understood, especiallywith respect to the interaction between two GBs.
Therefore, in this study, we have attempted toelucidate mechanisms behind GB interactions
through in-situ observations during crystal growth.
Experiments were performed using an in-situ
observation system consisting of a microscope anda crystallization furnace. The solidified silicon crystal
sampleswereanalyzedusingelectronbackscattering diffraction (EBSD) to determine thegrain orientations and structure of the GBs.
Figure 1 shows a crystal/melt interface of mc-Si
during directional solidification, and Figure 2 shows
the results of EBSD analysis of the observed area.
Several grain boundaries, including small-angle
grain boundary (SAGB) and Σ3 GB were observedin the growing crystal. A pair of straight {111}Σ3 GBs,
confirmed by EBSD measurement (see Fig. 2(b-d)),grow slanting toward the lower-left region of the
figure. This pair of {111}Σ3 GBs met another pairgrowing from the lower part (Fig. 1(4)). Fig. 2(c)shows the convergence of two pairs of {111}Σ3 GBs
to produce a new Σ9 GB. This Σ9 GB later convergedwith a {111}Σ3 GB to form a new {111}Σ3 GB with adifferent growth direction, as shown in Fig. 2(c).
In contrast to this situation, Σ3 GBs did notinteract with SAGBs during the solidification. Fromthe in-situ observation snapshots shown in Fig. 1(3)and 1 (4), the SAGBs grew through the {111}Σ3 GBs
without changing their direction of growth. This was
confirmed by EBSD analysis, as shown in Fig. 2(d).
The misorientation of SAGB did not change before
and after the interactions with Σ3 GBs.
We also observed the interaction between two
SAGBs, as shown in Fig. 2(e). SAGB1 and SAGB2
converge and only one GB with a slightly higher
misorientation, referred to as SAGB3, remains.

Fig. 1 Observation of interaction between GBs at crystal/melt interface in Si.

Fig. 2 EBSD analysis for characterization of observedGBs.

In this way, usually, when two GBs meet at a
crystal/melt interface, a new GB is established (e.g.,Σ3+Σ3→Σ9 and SAGB +SAGB→SAGB). However,interestingly, no such reaction occurs between
SAGB and Σ3 GB, i.e., Σ3+SAGB→Σ3+SAGB, withno change of misorientation and direction.
References[1] L-C. Chuang, K. Maeda, H. Morito, K. Shiga, W. Miller, and K.
Fujiwara, Scr. Mater. 148, 37 (2018).

Kozo Fujiwara (Corresponding Author, Collaborative Research Center on Energy Materials/Crystal Physics Division)
E-mail: kozo@imr.tohoku.ac.jp
Shin-ichi Orimo (Head of Collaborative Research Center on Energy Materials)
E-mail: orimo@imr.tohoku.ac.jp
URL: http://www.e-imr.imr.tohoku.ac.jp/

48

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IMR KINKEN Research Highlights 2018

Investigation of Magnon Spin Valve Effects in Insulator Spintronics
International Collaboration Center (ICC-IMR)

I

nformation transport and processing by pure magnonic spin currents in insulators is a promising alternative toconventional charge-current driven spintronic devices due to reduced ohmic losses. During the stay at ICCIMR, magnetization orientation dependent detection of magnon spin currents was studied in Y3Fe5O12(YIG)|CoO|Co tri-layers. The detected spin signal depends on the relative alignment of the YIG and Co
magnetization. This demonstrates a magnon spin valve behavior with an effect amplitude of >120%.
In Fig. 1(a) the YIG/CoO/Co multilayer sample isschematically shown [1]. After determining themagnetic properties of YIG and Co, we study themagnon spin current detection as a function of the YIG
and Co alignment. Figures 1(c-f) show field-dependent
voltage signals induced by f = 4.5 GHz microwave
irradiation at T = 120 K. By means of specific fieldsweep sequences, parallel (d, e) as well as anti- parallel(c, f) alignment of YIG and Co is realized. In the parallelstate (Fig. 1(d, e)) a multipeak voltage signal appears
corresponding to two overlapping Lorentzian line
shapes of opposite sign. In the antiparallel state (Fig.
1(c, f)) a voltage peak of one polarity but with asignificant asymmetry is observed, which can be fitted
by two overlapping Lorentzian functions.
The comparison of all four datasets allows us toseparate and attribute the peaks to different effects: (i)the signal of the spin current generated in the YIG and
detected in the Co (Vsc, blue curves) and (ii) a second
signal that originates from the Co (Vsr, green curves)and potentially is due to spin rectification (SR).
The intriguing discovery in this experiment is thealignment-dependent amplitude of Vsc analogous to
the spin-polarized charge current transmission in aconventional spin valve. While Vsr is independent of therelative alignment of the layers, the amplitude of Vsc isabout 120% larger in the antiparallel state as comparedto the parallel state. Regarding the total voltage Vsc+sr,
a signal amplitude variation of up to 290% is observed.
References[1] J. Cramer, F. Fuhrmann, U. Ritzmann, V. Gall, T. Niizeki, R. Ramos,
Z. Qiu, D. Hou, T. Kikkawa, J. Sinova, U. Nowak, E. Saitoh, andMathias Kläui, Nat. Commun. 9, 1089 (2018).

Fig. 1 (a) Illustration of the investigated YIG|CoO|Co tri-layer system. A spin current Js induced in the YIG by FMR spin pumping,propagates through the CoO layer and is detected electrically in the Co layer via the inverse spin Hall effect. The relative magnetization
orientation of YIG and Co can be adjusted to be either parallel or antiparallel. (b) Typical anomalous Nernst effect hysteresis loop
observed at T = 120 K (field cooled at Hext = 90 kOe). (d)-(f) Field-dependent voltage signals detected induced by microwave
irradiation. The total signal is given by a superposition of two distinct signals Vsc and Vsr, the sign of which individually depend on
the YIG and Co orientation. The amplitude of Vsc furthermore depends on the relative alignment of YIG and Co. (From [1])Mathias Kläui (Corresponding Author, Johannes Gutenberg University Mainz)
E-mail: Klaeui@uni-mainz.de
http://www.klaeui-lab.de
Gerrit Ernst-Wilhelm Bauer (Head of International Collaboration Center)
E-mail: icc-imr@imr.tohoku.ac.jp
URL: http://www.icc-imr.imr.tohoku.ac.jp/

IMR KINKEN Research Highlights 201849

Research Centers

Neutrons for Advanced Materials Science
Center of Neutron Science for Advanced Materials

T

he Center of Neutron Science for Advanced Materials is a neutron facility, which has a background of novel
materials science in IMR. This center operates three neutron instruments in a research reactor facility JRR-3
under a general user program, and is now constructing a state-of-the-art neutron spectrometer at J-PARC/
MLF. We hope to contribute to the development of materials science and neutron science by utilizing theunique platform of the neutron instruments.
The Center of Neutron Science for Advanced
Materials (CN-IMR) was established in 2010 with theaim of promoting novel materials science by using
neutrons. The CN-IMR operates two neutron
spectrometers and one diffractometer at the JRR-3
research reactor in the Japan Atomic Energy
Agency and is now constructing a state-of-the-art
polarized neutron spectrometer, POLANO, with anintense neutron source at the Materials and Life
Science Experimental Facility (MLF) in the Japan
Proton Accelerator Research Complex (J-PARC)[1,2]. POLANO will achieve polarization analysis inhigher energy regions beyond the measurements
performed by a triple-axis spectrometer at a reactorbased neutron source, and thereby, provide a huge
opportunity for research in the field of strongly
correlated electron systems. The construction of
POLANO started in 2012 under the collaboration
with the High Energy Accelerator Research
Organization (KEK). After the construction of themain part of the instruments, we have finallysucceeded in receiving the first neutron beam at
POLANO on 21 June. The spectrometer will beoffered for the collaborative research programs of
IMR after the commissioning process.
In order to discuss future neutron researchbrought through new materials and the unique
instruments at J-PARC and JRR-3, including
POLANO, we held a two-day workshop,“Complementary use of J-PARC and JRR-3 in
Neutron Science Research.” Approximately fifty
material and neutron scientists attended theworkshop and exchanged information. The strategic
use of the neutron facility and neutron instrument
was also discussed. The workshop was wellreceived by the participants. Furthermore, topromote the utilization of neutrons for condensed
matter physics and materials science, we distributed
leaflets for the advertisement of our spectrometers
to the participants as well as research groups inJapan.

Fig. 1 Photograph of some of the POLANO project
members. We have succeeded in receiving the firstneutron beam at POLANO installed in J-PARC/MLF.

Fig. 2 Photograph of workshop held in IMR. More thanforty scientists participated and discussed the future
neutron science.

References[1] T. Ino, M. Ohkawara, K. Ohoyama, T. Yokoo, S. Itoh, Y. Nambu,
M. Fujita, H. Kira, H. Hayashida, K. Hiroi, K. Sakai, T. Oku, and
K. Kakurai, J. Phys. Conf. Ser. 862, 012011/1-012011/11 (2017).
[2] M. Ohkawara, T. Ino, Y. Ikeda, T. Yokoo, S. Itoh, K. Ohoyama,and M. Fujita, J. Phys. Conf. Ser., (2018) in press.

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

50

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IMR KINKEN Research Highlights 2018

Quantum Fluctuation-Dominated States in Highly Crystalline
Two-Dimensional Superconductors
Laboratory of Low Temperature Materials ScienceT

wo-dimensional (2D) superconductors with high crystallinity have been new platforms for the novel quantum
phenomena. Here, we provide a universal field versus temperature phase diagram of such clean 2D
superconductors, including a variety of quantum fluctuation-dominated states and quantum phase transitions,which is totally different from that of conventional or dirty 2D superconductors, by using gate-induced electron
systems.
Bc*

Weakly localized metal

Magnetic fieldTwo-dimensional (2D) superconductors havebeen well-known platforms for the study of a quantum
phase transition (QPT) occurring at zero temperature.
The superconductor–insulator transition (SIT) tuned
by magnetic field is one of the remarkablephenomena of QPT. Such a QPT was predominantly
investigated in dirty superconductors in the form of
granular or amorphous thin films, because thelocalization effect of superconducting electrons or
vortices by disorder plays a significant role for SIT.
However, it has been long argued how the QPT andthe quantum phases evolve with the weakening of
the effect of disorder. Recently, our group found thatthe gate-induced superconducting surface of a
ZrNCl single crystal indicates the quantum metallic/vortex liquid state with non-zero electrical resistanceby applying a very small field far below the mean
field critical field Bc2MF at the low temperature limit[1]. Thus, the conventional picture for the fieldinduced SIT needs to be modified, and the transition
from the quantum metallic state to the normal state at
low temperature emerges as a new subject of the
QPTs in highly crystalline 2D superconductors withminimal disorder.
Here, we propose a comprehensive field –temperature (B–T) phase diagram of highly
crystalline 2D superconductors, which is composedof two thermal fluctuation regions and two quantum
fluctuation regions, as shown in Fig. 1. Based on
detailed analyses of magneto-transport properties in
ion-gated ZrNCl and MoS2, we found that these 2D
superconducting systems commonly show a wide
range of a quantum phase stemming from the very
low magnetic field at low temperature, which transfer
to the weakly localized metal through the quantum
critical point (QCP). In particular, the observed QPT
has a character known as the quantum Griffiths
singularity with the critical exponent diverging toward
the QCP, which is distinct from that of the conventional

Quantum
Griffiths
state
MF

Bc2

SC
Th

er

Quantum
metal

BSM

Thermalcreep

SC state (R = 0)

TBKT

m

al

flu

ct

ua

on

se

t

tio

n

Tc0

Temperature

Fig. 1 Magnetic field vs. temperature (B–T) phase diagramof highly crystalline 2D superconductors [2]. Tc0 is themean field transition temperature and TBKT is theBerezinskii–Kosterlitz–Thouless temperature. The data
points are various crossover temperatures or fields
obtained from the analyses of resistive transition curves.

SIT with a constant exponent. This implies that thecritical state (quantum Griffith state) below the QCP
is described by so-called rare regions, interpreted
as superconducting puddles surviving in the normal
state background at T → 0 K.
The present result strongly indicates thatquantum fluctuation dominates the wide quantum
metallic state and its crossover to the quantum
Griffiths state, which appears as a generic feature ofhighly crystalline 2D superconductors.
References[1] Y. Saito, Y. Kasahara, J. Ye, Y. Iwasa, and T. Nojima, Science.
350, 409 (2015).
[2] Y. Saito, T. Nojima, and Y. Iwasa, Nat. Commun. 9, 778 (2018).

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

IMR KINKEN Research Highlights 201851

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 around the world for studying thephysical and chemical properties of radioactive materials, such as actinide compounds. Researchers frommany of the leading universities and institutes all over the country visit this facility every year to prepare a variety
of materials and carry out chemical and physical measurements.

The Laboratory of Alpha-Ray Emitters provides a
research environment for the study of 170 radionuclides(RIs) and elements, especially alpha-ray emitterssuch as actinides. This laboratory functions as asource for the preparation of pure crystals of actinide
compounds, providing them to other universities and
to Synchrotron Orbital Radiations (SORs). The
Radiation Controlled Area of this laboratory includes
three chemistry labs and three physical labs, which
are equipped with local exhaust ventilation systems
enabling the handling of various types of materials.
Many spectrometers including those for gamma-rays
and alpha-rays are available.
Recently, lanthanide or uranium-based singlemolecule magnets (SMMs) have attracted muchattention [1, 2]. In these compounds, the large
magnetic anisotropy and the strong spin–orbit
interaction reduce the rate of magnetic relaxations. In
most uranium-based SMMs, uranium (III) is usedinstead of uranium (IV). However, it is important tostudy the magnetization of uranium (IV) complexes tounderstand the relationship between magnetic
anisotropy and magnetic relaxations. In this study, we
aim to observe slow magnetic relaxations onbisphthalocyaninato-uranium(IV)complex(UC64H32N16) as an SMM example of an f2 system.
This complex has an identical structure to that of thewell-studiedbisphthalo-cyaninato-lanthanide
complexes, such that we can compare the actinidebased SMM with lanthanide-based SMMs.
As a precursor of uranium (IV), we preparedUCl4. A mixture of UCl4 and phthalonitrile (C6H4(CN)2)
in a 1:10 molar ratio in a glass test tube was purged
with Ar, and heated to 250°C. A dark-green solid
obtained, washed with water and ethanol, and thendried under vacuum. The crude product was placedin a quartz tube, evacuated to 10−3 Torr and heated to
450°C. The purified product was obtained in the tube
with a temperature gradient.

Fig. 1 Magnetization curve of bisphthalocyaninato-uranium(IV)indicated in Bohr magneton units. The sweeping external
magnetic field: 0→90 k→−90 k→90 k→0 Oe. The
magnitude of magnetization approaches 1 µB. A small
hysteresis was observed in the positive magnetic field area.
However, a slow magnetic relaxation phenomenon was notobserved by AC magnetic measurement. Inset left: The
molecule structure of UPc2 and its stack in the crystal. Inset
right: The UV–Vis spectrum of UPc2. UPc2 has Q-band in
the range of 580–700 nm, which is attributed to the π→π*transition of phthalocyaninato-rings.

The magnetic susceptibility of the lanthanide anduranium complexes in the constant and alternating
magnetic field were measured using the PPMS [3]. In
the case of the uranium complex, no SMM behavior
was observed. It is conjectured that the energy
separation between the lowest and second lowest
substates is insufficient to exhibit the slow magnetic
relaxation behaviors.
References[1] N. Ishikawa et al. J. Am. Chem. Soc. 125, 8694 (2003).
[2] J. D. Rinehart et al. J. Am. Chem. Soc. 131, 12558 (2009).
[3] T. Fukuda et al. Dalton Trans. 46, 12421 (2017).

Tomoo Yamamura (Corresponding author, Department of Nuclear Engineering, Kyoto University)
E-mail: yamamura@imr.tohoku.ac.jp
Ryuta Kasada (Head of Laboratory of Alpha-Ray Emitters)
URL: http://alpha.imr.tohoku.ac.jp

52

IMR KINKEN Research Highlights 2018

IMR KINKEN Research Highlights 2018

Reliable and Precise Quantifications of Elemental Constituentsin Steel Materials
Analytical Research Core for Advanced Materials

Offers of elemental analyses are routinely accepted to provide the chemical composition in various metal and

25
20
15
10

0

1

2

3

4

5

Surface area / cm2
Fig. 1 Relationship between the analytical value of oxygen
and the surface area in JSS GS-2c sample.

Slope of calibration curve

The Analytical Research Core for Advanced
Materials (ARCAM) uses various instrumental
analyses, such as inductively coupled plasma
atomic emission spectrometry, atomic absorption
spectrometry (AAS), and gaseous CS/ON/H
analyses. This report describes two analyticalimprovements in analysis of metallic materials that
we suggested in 2017.
The oxygen content in a steel sample was
accurately evaluated using a simple pre-treatment
in inert gas fusion–infrared absorption spectrometry[1]. An over-estimated analytical value might beobtained in the oxygen quantification of steel
samples because of surface-absorbed and surfacereacted oxygen. Several pieces of the specimen
with different masses were prepared (e.g., columnshaped specimens of steel reference material (RM;
JSS GS-2c) with masses 0.1, 0.2, 0.25, 0.5, and 1 g).
The oxygen content values of these specimens
were proportional to the surface area (Fig. 1).
Therefore, a surface-oxygen-free analytical value ofthe oxygen content in the steel RM could be
estimated by extrapolating this relation to beapproximately 13.5 µg g−1.
A sequential internal standard method in flame,
AAS was investigated for quantifying the alloyednickel in a steel sample [2]. The nickel/ironabsorbance ratio was used for the improvement ofanalytical precision. Relationships between theabsorbance and iron concentration and the rangesof their linear calibration were tested for 23 ironatomic lines as the internal standard line. The results
indicated that an allowable range of the concentration
could be predicted from the product of the relative
number density and the transition probability of theabsorption lines (Fig. 2).

Oxygen content / µg g-1

inorganic materials. Better accuracy, precision, and sensitivity of our analyses would be conducted on thebasis of analytical improvements. Our recent studies on such an improvement are demonstrated.

0.04
0.03
0.02
0.01
0.00

0

10 20 30 40 50

gA value × relative number density
Fig. 2 Relationship between the slope of the calibration
curve and the sensitivity factor (gA value × relative
number density).

References[1] T. Chiba, K. Wagatsuma, K. Takada, and K. Abiko, Tetsu-toHagane. 104, 61 (2018).
[2] T. Itagaki, T. Ashino, and K. Wagatsuma, Bunseki Kagaku 66,
515 (2017).

Kenichi Nakayama (Corresponding Author, Analytical Research Core for Advanced Materials)
E-mail: ken1naka@imr.tohoku.ac.jp
Kazuaki Wagatsuma (Head of Analytical Research Core for Advanced Materials)
E-mail: wagatuma@imr.tohoku.ac.jp
URL: http://bunseki-core.imr.tohoku.ac.jp/

IMR KINKEN Research Highlights 201853

Author Index
NamepageNamepage
Mohri, Tetsuo

A
Akiyama, Eiji
Amiya, Kenji11
46

Aoki, Dai37

N
Nagai, Yasuyoshi
Nagumo, Kazuaki

49

Nakayama, Kenichi
Nojima, Tsutomu
Nojiri, Hiroyuki

B
Bauer, Ernst-Wilhem Gerrit
C
Chiba, Akihiko
F
Fujita, Masaki

33, 50Fujiwara, Kozo 
Furuhara, Tadashi

8, 48
44

G
Goto, Takashi

25

HHaga, YoshinoriHarada, Takayuki
Hashimoto, Kenichiro
Hashimoto, Yusuke

43
31
32
30

I
Ichitsubo, Tetsu
Inoue, Koji
K
Kanazawa, Naoya
Kasada, RyutaKato, Hidemi
Kläui, MathiasKubo, Momoji
LLeón, AlejandroM
Masahashi, Naoya
Matsuoka, TakashiMiyasaka, Hitoshi

54

13

IMR KINKEN Research Highlights 2018

21
19

45
52
22
49
10, 47

28

46
20
34

39

19, 42, 43
19
53
51
29, 45

Nozawa, Jun36

O
Ohno, Yutaka18

Ono, Kanta
Orimo, Shin-ichi

47
23, 48

S
Saitoh, Eiji
Sasaki, Takahiko
Semboshi, Satoshi
Shimizu, Yasuo
Shiraishi, Takahisa
Simura, Rayko
Sugiyama, Kazumasa

30
51
44
19
38
12
12

T
Takagi, Shigeyuki
Takahashi, Masae

23
47

Takanashi, Koki
Taniguchi, Kouji

35
34

Tsukahara, Hiroshi

47

W
Wagatsuma, Kazuaki

14, 53Wei, Daixiu

15

Y
Yamamura, TomooYamanaka, KentaYamazaki, Kaoru

52
13
39

Yoshida, Kenta
Yoshikawa, Akira

42
24

Z
Zhang, Yongjie

9Keyword Index
Keywordpage

Keywordpage

A
alloy

molecular dynamics

10

13, 24

multi-ferroics29

atomic emission spectrometry

14

Bbulk metallic glassNnanostructure15

22

neutron diffraction

29

nuclear materials

19

nucleation & growth36O
optical properties

20

C
chemical vapor deposition (CVD)

25

colloid36
corrosion

11, 15crystal growth8, 24, 36

organic

32, 39crystal structure

12, 21, 23

oxide

21, 31

13, 18, 20Pphase transformation

D
defects9

deformation22

photocatalytic25

devices31

piezoelectric38

E
electron doping

plasma diagnostic

14

positron annihilation

19electronic structureenergy storage
F
first-principles calculations34
33, 3921
23, 39fracture10
Gglow discharge plasma

14

Q
quasicrystal12Rrare earths

28

S
simulation10
solar cells

18

glass32

spectroscopy30

H
heavy fermion

spin dynamics

35

37

spin wave

30

high-magnetic field

29

spintronics28

high strength steel

11

steel9hydride23

strength13hydrogen evolution

25

superconducting33, 37hydrothermal38

surface reaction

11, 15I
interface

Tthin films

31, 38M
magnetic properties

8, 9, 18

3D structure34, 3520

magnetism30

Vvacancy19

mechanical properties

voltage28

22

metal24
metal-insulator transition

32

X
X-ray diffraction (XRD)

12

molecular beam epitaxy (MBE)

35

X-ray scattering33

molecular devices

34

IMR KINKEN Research Highlights 201855

Editors
Kozo Fujiwara, Ryuta Kasada,
Yoshinori Onose, Shigeyuki Takagi,
Takeshi Seki, and Norihiko Okamoto

Editorial Staff
Misa Y. Tomimatsu, Aki Oikawa, and Maki Sugawara

Printing
HOKUTO Corporation

Organization
Institute for Materials Research
Tohoku University
2-1-1 Katahira, Aoba-ku, Sendai 980-8577, Japan
Tel. +81-(0)22-215-2144 Fax. +81-(0)22-215-2482
URL: http://www.imr.tohoku.ac.jp/
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