KINKEN
Research Highlights
2017

Institute for Materials Research, Tohoku University

KINKEN Research Highlights 2017
Contents
Preface���������������������������������������������������������������������������������������������������������������������������������������������������������� 4
Research Highlights
1. Infrastructural Materials
Microstructure Design of Structural Metallic Materials Division�������������������������������������������������������������������� 8
Nuclear Materials Science Division�������������������������������������������������������������������������������������������������������������� 9
Multi-Functional Materials Science Division����������������������������������������������������������������������������������������������� 10
Deformation Processing Division����������������������������������������������������������������������������������������������������������������11
Materials Science of Non-Stoichiometric Compounds Division����������������������������������������������������������������� 12
Analytical Science Division������������������������������������������������������������������������������������������������������������������������ 13

2. Energy-related Materials
Crystal Physics Division����������������������������������������������������������������������������������������������������������������������������� 16
Physics of Crystal Defects Division������������������������������������������������������������������������������������������������������������ 17
Materials Design by Computer Simulation Division������������������������������������������������������������������������������������ 18
Nuclear Materials Engineering Division������������������������������������������������������������������������������������������������������ 19
Non-Equilibrium Materials Division������������������������������������������������������������������������������������������������������������� 20
Hydrogen Functional Materials Division����������������������������������������������������������������������������������������������������� 21
Creation of Life Innovation Materials for Interdisciplinary and International Researcher Development��������� 22
Professional development Consortium for Computational Materials Scientists (PCoMS)�������������������������� 23

3. Electronic Materials
Theory of Solid State Physics Division������������������������������������������������������������������������������������������������������� 26
Magnetism Division������������������������������������������������������������������������������������������������������������������������������������ 27
Surface and Interface Research Division��������������������������������������������������������������������������������������������������� 28
Low Temperature Physics Division������������������������������������������������������������������������������������������������������������� 29
Low Temperature Condensed State Physics Division�������������������������������������������������������������������������������� 30
Metal Physics with Quantum Beam Spectroscopy Division����������������������������������������������������������������������� 31
Irradiation Effects in Nuclear and Their Related Materials Division������������������������������������������������������������ 32
Physics of Electronic Materials Division����������������������������������������������������������������������������������������������������� 33
Chemical Physics of Non-Crystalline Materials Division���������������������������������������������������������������������������� 34
Solid-State Metal-Complex Chemistry Division������������������������������������������������������������������������������������������ 35
Magnetic Materials Division������������������������������������������������������������������������������������������������������������������������ 36
Crystal Chemistry Division������������������������������������������������������������������������������������������������������������������������� 37
Advanced Crystal Engineering Laboratory������������������������������������������������������������������������������������������������ 38
Actinide Materials Science Division����������������������������������������������������������������������������������������������������������� 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
Research and Development Center for Ultra High Efficiency Nano-Crystalline Soft Magnetic Materials�� 51
Laboratory of Low Temperature Materials Science������������������������������������������������������������������������������������ 52
Laboratory of Alpha-Ray Emitters�������������������������������������������������������������������������������������������������������������� 53
Analytical Research Core for Advanced Materials (ARCAM)������������������������������������������������������������������� 54

Author Index����������������������������������������������������������������������������������������������������������������������������������������������� 55
Keyword Index������������������������������������������������������������������������������������������������������������������������������������������� 56

Preface

Dear Colleagues,

We are pleased to present KINKEN Research Highlights 2017, 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,

4

IMR KINKEN Research Highlights 2017

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 20175

Infrastructural Materials

IMR KINKEN Research Highlights 2017

Research

Infrastructural Materials

Mechanism of Abnormal Grain Boundary Ferrite Formation inHypereutectoid Pearlitic Steels

Strengthening of steel wires made from hypereutectoid pearlitic steels enables us to construct long-spansuspension bridges. However, the deterioration of ductility of the wire caused by grain boundary ferrite (GB-α)formation poses a serious problem for the applications of high strength steel wires. Therefore, the formation
mechanism of GB-α was investigated from the viewpoint of crystallography of phase transformation.

There is a strong demand for high strength
steel wires for the construction of long suspension
bridges, which can not only greatly reduce thebridge weight, but also the cost and the construction
time. Steel wires are produced from high carbon
pearlitic steels, and the formation of grain boundary
ferrite (GB-α) insuch steels, as shown in Fig. 1,
deteriorates the ductility of the steel wires. Since it isgenerally believed that a fully pearlitic structure
forms in the eutectoid steels, the formation of GB-αin eutectoid or even hypereutectoid steels is,therefore, unusual.
Thus, the effects of temperature and carbon
content on the formation of GB-α were investigatedto elucidate its formation mechanism [1]. It was foundthat the volume fraction of GB-α increases withdecreasing transformation temperature, carbon
content, and the prior austenite grain size. Pearlite
nucleated at the prior austenite grain boundary
usually grows into one of the austenite grain
separated by the grain boundary, while GB-α forms
on another austenite grain. Orientation analyses
reveal that GB-α and pearlitic-α possess the sameorientation, indicating that an α grain grows as
pearlite in one of the austenite grains and as GB-α inanother austenite grain. By applying a reconstruction
method of austenite orientation from martensite [2], it
was shown that such morphology difference resulted
from the difference in orientation relationship (OR)between α and austenite, i.e., a near KurdjumovSachs (K–S) OR and a non K–S OR with GB-α andpearlite, respectively (Fig.2). Consequently, it was
proposed that the suppression of cementite
nucleation at the ferrite/austenite boundary having anear K–S OR is the reason for the formation of GB-αduring low temperature transformation.

Fig. 1 Typical GB-α and pearlite structures in high carbon
steels. PAGB: prior austenite grain boundary

Fig. 2 Effect of OR on the evolution of GB-α in high carbon
pearlitic steels. K-S: Kurdjumov-Sachs orientation
relationship.

References[1] G. Miyamoto, Y. Karube, and T. Furuhara, Acta Mater. 103, 370(2016).
[2] G. Miyamoto, N. Takayama, and T. Furuhara, Scripta Mater.
60, 1113 (2009).

Keywords: steel, phase transformation, nucleation & growth
Goro Miyamoto (Microstructure Design of Structural Metallic Materials Division)
E-mail: miyamoto@imr.tohoku.ac.jp
URL: http://www.st-mat.imr.tohoku.ac.jp/en/index.html

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IMR KINKEN Research Highlights 2017

IMR KINKEN Research Highlights 2017

Influence of Atmospheric Corrosion Environment on the
Hydrogen Entry Behavior

Hydrogen entry behavior in atmospheric corrosion environments has been investigated by the means ofelectrochemical hydrogen permeation test using Fe sheet specimens outdoor-exposed in Okinawa and Beijing.
We found that the exposure at Beijing resulted in remarkably higher hydrogen uptake than did at Okinawa, andthat environmental factors such as air pollutants have a strong influence on the enhancement of hydrogen
entry.
Hydrogen embrittlement (HE) is of great
importance for the safety and reliability of highstrength steels. We investigated the role of hydrogenin damage evolution in metallographic structures [1]and proposed an evaluation method for the HE
property of high strength steels. In addition, toexamine the effects of hydrogen on the mechanicalproperties of steels, we essentially need tounderstand hydrogen uptake from service
environment to evaluate the susceptibility of steels
to HE for practical usage.
In order to assess hydrogen entry in an
atmospheric corrosion environment where many
types of structural steels are used, we adopted theelectrochemical hydrogen permeation test (ECHPT),
which enabled us to monitor hydrogen entry not
only under electrochemical hydrogen charging
condition [2], but also under atmospheric corrosion
condition where a relatively low concentration ofhydrogen is introduced.
We exposed Fe sheet specimens to outdoor
conditions in Okinawa and Beijing and performed
ECHPT on the exposed Fe sheets under controlledtemperature and humidity in our laboratory tosimulate atmospheric corrosion accompanied byhydrogen entry [3].
Figure 1 shows the representative changes inhydrogen permeation current density, which is
proportional to the flux of introduced hydrogen, witha change in applied relative humidity. The specimen
atmospherically corroded in Beijing for 4 months
showed a remarkable increase in hydrogen
permeation current density under wet condition. In
contrast, the specimen exposed in Okinawa, where
corrosivity is relatively high due to airborne salt andthe climate, showed only a small increase inhydrogen permeation current density under wet
condition with a hydrogen entry peak during thedrying process after wetting.
Surface analyses showed that the deposition of
S-containing substances and nitrate on the Beijing-

Fig. 1 Changes in hydrogen permeation current density of
specimens with change in applied relative humidity at
30 °C [3].

exposed specimen was more remarkable than thaton the Okinawa-exposed specimen, though thedegree of corrosion in Beijing was less than that in
Okinawa. Presumably, the deposition of SOx- andNOx-related air pollutants and the particulate matters
containing them have a strong influence on theenhancement of hydrogen entry, which is ascribedto the acidification of the exposed specimen surface.
References[1] M. Koyama, C. Tasan, E. Akiyama, D. Raabe, and K. Tsuzaki,
Philos. Mag. Lett. 96, 9 (2016).
[2] E. Akiyama, and S. Li, Corros. Rev. 34, 103 (2016).
[3] E. Akiyama, S. Li, H. Katayama, B. Zhang, K. Zhao, and W.
Oshikawa, ISIJ Int. 56, 436 (2016).

Keywords: corrosion, high strength steel, surface reaction
Eiji Akiyama (Nuclear Materials Science Division)
E-mail: akiyama@imr.tohoku.ac.jp
URL: http://www.imr.tohoku.ac.jp/en/about/divisions-and-centers/research-division/12.html

IMR KINKEN Research Highlights 20179

Infrastructural Materials

High-Hardness Diamond Composite Consolidated under
Moderate Pressure and TemperatureDiamond is the hardest material on Earth and its compacts are used as powerful cutting tools for ultra-precise
machining. We synthesized a highly dense and high-hardness diamond-based composite by spark plasma
sintering under 100 MPa using SiC-coated diamond powder prepared via chemical vapor deposition.
Polycrystalline diamond is an excellent cutting
tool for ultra-precise machining because of its
extraordinarily high hardness. Diamond compacts
such as those in tipped tools can be manufactured
by sintering under ultra-high pressures above
several gigapascals and at high temperatures
above 2500 K. To consolidate diamond powders,high sintering temperatures are necessary owing to
its strong covalent bonding. Hence, ultra-highpressure is required during the sintering processsince diamond instantly transforms into graphite athigh temperatures, as it is thermodynamicallyunstable under moderate pressures below
megapascals.
We have proposed a new approach toconsolidate diamond powders into dense and hardcompacts under moderate pressures by the
combination of chemical vapor deposition (CVD)and spark plasma sintering (SPS). Diamondpowders were coated with nanolayers of siliconcarbide (SiC) by a rotary CVD technique that has
been developed by us [1, 2]. Rotary CVD enables
us to deposit a uniform thin layer on the diamondparticles several micrometers in size (Fig. 1(a) and(b)) [3]. The SiC-coated diamond powders with theaddition of silica powders was rapidly consolidated
by SPS at a sintering temperature of 1873 K under
100 MPa. The resultant diamond-based composite
possessed a fully dense morphology comprisingdiamond grains dispersed in silica matrix, forming afine mosaic structure (Fig. 1(b)). Under the same
sintering conditions and without the coated SiC
layers or silica, diamond transformed into graphite
and reacted with silica, and hardly attained highdensities. The CVD-SiC layer prevented a directcontact between diamond and silica, leading to theformation of compatible and densely packed
interfaces
betweenthem
that
enhancedconsolidation by viscous flow sintering. The resultant
diamond-based composite exhibited high hardness(Vickers hardness above 35 GPa). Since the thermal
expansion coefficient of silica is lower than that of
diamond and SiC, compressive stress could be

Fig. 1 (a) and (b) TEM bright field images of SiC-coateddiamond powder by rotary CVD; (c) SEM image of adiamond-based composite prepared by SPS of the
SiC-coated diamond powder with silica powder; and(d) EELS mapping of the interface of diamond and silica
in the diamond-based composite.

applied to silica during cooling from the sintering
temperature, resulting in an enhancement in thehardness and toughness of the diamond-based
composite.
References[1] Z. He, H. Katsui, R. Tu, and T. Goto, J. Am. Ceram. Soc. 97,
2423 (2014).
[2] H. Katsui, Z. He, and T. Goto, J. Jpn. Soc. Powder Powder
Metallurgy 63, 111 (2016).
[3] Z. He, H. Katsui, R. Tu, and T. Goto, J. Am. Ceram. Soc. 99,
1862 (2016).

Keywords: chemical vapor deposition, sintering, microstructure
Takashi Goto and Hirokazu Katsui (Multi-Functional Materials Science Division)
E-mail: goto@imr.tohoku.ac.jp
URL: http://www.goto.imr.tohoku.ac.jp/index.html

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IMR KINKEN Research Highlights 2017

IMR KINKEN Research Highlights 2017

Impact of Solute Elements on Detwinning in Magnesium
and Its Alloys

Twinning and detwinning behaviors of {1012} twins in pre-compressed pure Mg and AZ31 and AZ91 alloys

were investigated systematically. We found that the solute elements, Al and Zn, and the resultant precipitates
disrupt the synchronous motion of atoms in the twinning boundaries during twin formation, yielding a large
amount of incoherent twin boundaries (TBs) and low-angle boundaries from the pre-existing TBs after
detwinning, which became more significant with increasing amount of solute elements.

Twinning represents an important deformation
mode in Mg alloys, which have a hexagonal closepacked (HCP) crystalline structure, because they
do not have sufficient slip systems for continuous
plastic deformation as in polycrystals. In general,
twin in pure Mg and its alloys is not stable, and may
either grow or shrink (detwin) under further
deformation. For this reason, twin-boundary (TB)
motion affects the performances of Mg alloys inmany respects such as fatigue, strength,
pseudoelasticity, and damping capacity [1].
To clarify the TB motion mechanism to further
optimize the properties of Mg alloys, it is crucial tounderstand more comprehensively the effect ofsolute elements on both the twinning and detwinningbehaviors. We offer a direct observation of thedetwinning behavior of pre-compressed pure Mg
and Mg alloys, AZ31 and AZ91, through tensile tests
with in-situ electron backscattering diffraction(EBSD), as shown in Fig. 1. We demonstrate, for the
first time, the impact of solute elements on the
detwinningbehavior
andtheassociatedmicrostructures of Mg alloys by combining finite
element analysis, compressive tests, reverse tensile
tests, in-situ EBSD, and high-resolution transmission
electron microscopy [2].
Both twinning and detwinning are intrinsicallyrelated to the mobility of TB. Firstly, we adopted theconcept of friction stress and back stress formed
because of the non-uniformity of stress distribution
near TB to evaluate the difference between the TB
mobilities in pure Mg and Mg alloys, AZ31 and
AZ91. Both the friction stress and back stress were
found to increase with increasing alloying element.
During twinning, the misorientation angle
between the matrix and the twin (i.e., the angle
between the basal planes in matrix and twin)
deviated from the ideal angle (86.3°) due to a
resistance from the matrix. This deviation was moresignificant with increased content of alloying
elements due to a large local tension strain in the
crystalline lattice generated by the solute atoms,
yielding a large amount of incoherent TBs. In thiscase, more low-angle boundaries (2-5°) might have

3%

1%
(a)

6%

(b)

(c)

(d)

(f)

(g)

(h)

(j)

(k)

(l)

8%

Pure Mg

100mm

(e)

AZ31
100mm

(i)

AZ91

100mm

Fig. 1 Inverse
polar figures of pre-compressed pure Mg,
Fig. 1 Inverse polar figures of pre-compressed pure Mg, AZ31 alloy, and
AZ91 alloy after tension to engineering strain levels of 1, 3, 6, and 8%.
AZ31 alloy,
and AZ91 alloy after tension to engineeringstrain levels of 1, 3, 6, and 8%.

Fig. 2 Schematic illustration of the formation of low-angle
boundaries.

been reserved in the Mg alloys after detwinning, as
schematically shown in Fig. 2.
In addition, the tendency of detwinning via thereverse motion of TB weakened with an increase in
the solute-element concentration. The secondary
twins were also formed remarkably in the interior of
the primary twins in Mg alloys with a high soluteelement concentration, as indicated by the blackarrows in Fig. 1, owing to the low mobility ofincoherent TB and the variation of local stress stateby the precipitates.
References[1] Y.J. Cui, Y.P. Li, S.H. Sun, H.K. Bian, H. Huang, Z.C. Wang, Y.
Koizumi, and A. Chiba, Scr. Mater. 101, 8 (2015) .
[2] Y.J. Cui, Y.P. Li, Z.C. Wang, X. Ding, Y. Koizumi, H.K. Bian, L.Y.
Lin, and A. Chiba, Int. J. Plast. 91, 134 (2017).

Keywords: alloy, deformation, microstructure
Akihiko Chiba (Deformation Processing Division)
E-mail: a.chiba@imr.tohoku.ac.jp
URL: http://www.chibalab.imr.tohoku.ac.jp/english/index.html

IMR KINKEN Research Highlights 201711

Infrastructural Materials

Precipitation Behavior in Age-Hardened Die-Cast AluminumAlloys Studied by Transmission Electron Microscopy

Strengthening of die-cast alloys was a tough problem due to the microstructural imperfections incurred during
processing, and not much was known until quite recently on the structural evolution of the precipitated phases
in aluminum-based alloys. Latest progresses in the processing and characterization made it possible to reveal
the early stages of phase transformation in the commercially available aluminum alloys.

Even though the transformation behaviors
during heat-treatments in aluminum (Al) alloys havebeen known for a long time, surprisingly, only asmall amount of information was available on thecommercial grade die-cast Al alloys because of the
intrinsic two-phase nature of the alloys and theubiquitous presence of defects such as porosity.
With the advent of squeeze die-casting, it is now
possible to manufacture die-cast Al alloys free fromsuch imperfections and carry out conventional
ageing. Here, we report the structural evolution of
an Al alloy prepared through a newly developed
squeeze die-casting technique, with a composition
similar to that of JIS ADC12.
The alloy was aged at 453 K with or without aprior solution treatment. The former annealing
technique, known as T6-treatment, increased thehardness of the alloy [1]. Using transmission electron
microscopy (TEM), we investigated the precipitates
responsible for age-hardening. In particular, we
employed high-angle annular dark field scanningtransmission electron microscopy (HAADF-STEM)
in order to understand the partitioning of the added
elements. Our compositional analysis revealed thatthe alloying elements, including silicon (Si), copper(Cu), and magnesium (Mg) led to the formation ofseveral types of precipitates in the face-centeredcubic (fcc) matrix Al-phase during aging. Precipitates
exhibiting an equiaxed shape with Cu-enrichedfaces at the interface with the matrix were observed.
We suggest that these precipitates have an fcc
structure containing Si, Cu, and Mg atoms that
substitute for Al. Prolonged aging caused theformation of another type of precipitate with anelongated shape, which were identified as the S”phase. Some regions within the precipitates of theS”-phase transformed into the Q-phase with anincreasing Si content in the precipitates. Precipitatesof the S-phase and the θ’-phase were also formedby over-aging.

Fig. 1 HAADF-STEM images and NBD patterns of anequiaxed precipitate (a and b) and an elongatedprecipitate (c and d) obtained from the precipitates
formed in the Al-phase during aging at 453 K for 691.2
ks of T6 treatment.

Fig. 2 HAADF-STEM image of a precipitate. Projection of
structure of the θ’-phase along the [100]θ’ axis isinserted. The white and grey spheres represent Cu and
Al atoms, respectively.

References[1] T.J. Konno, S. Sasaki, and T. Hamaoka, J. Jpn. Inst. Light
Metals 66, 291 (2016).

Keywords: aluminum alloys, age-hardening, phase transformation
Toyohiko J. Konno (Materials Science of Non-Stoichiometric Compounds Division)
E-mail: tjkonno@imr.tohoku.ac.jp
URL: http://konno-lab.imr.tohoku.ac.jp/

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IMR KINKEN Research Highlights 2017

Rapid Detection of Distribution of Alumina Inclusions in
Ferric Stainless Steels by Laser-Induced Breakdown
Spectroscopy (LIBS)

Since micron-sized aluminum inclusions in steel products have been recognized as a source of cracks, laser-induced breakdown spectroscopy (LIBS) has been adopted for rapid detection of these particles. A single shotof pulsed laser onto the alumina inclusions in ferric stainless steel clearly showed the emission signals from theablated aluminum atoms/ions.

Alumina inclusions contaminate steel products
mainly during the process of deoxidation and are
known to deteriorate the performance of the steel
products. The size of these inclusions should becontrolled around 5~40 micrometer diameter. The
diameter, number, and distribution of theseinclusions are evaluated according to the JIS G
0555 standard, “Microscopic testing method for the
non-metallic inclusions in steel”. However, thismethod is based on visual counting using an optical
microscope and tends to be tedious and time
consuming.
Considering these situations, we
adopted laser-induced breakdown spectroscopy(LIBS) to detect alumina particles and theirdistribution in ferric stainless steels. The principal of
LIBS is as follows: when a pulsed laser with highenergy density is focused onto the surface of a
specimen, the atoms in that spot receive energy
from the laser and is ablated into a laser plasma.
Inside the laser plasma, the ablated atoms/ions are
excited/de-excited and results in an optical emission.
In this study, a small plate of ferric stainless steel
was placed on the LIBS system described below,
and alumina inclusions were detected by LIBS withreal-time monitoring of the surface of the specimen.
The laboratory-made LIBS setup mainlycomprised a Nd:YAG laser, (LS-2137, LOTIS TII),
Czerny-Turner-type
imaging
spectrometer(MS7504i, SOL Instruments), and an intensified
CCD camera (DH334T, Andor Technology), as
illustrated in Fig. 1. The real-time monitoring system
was equipped with a combination of a prism mirror,
a macroscopic lens (TS-9303N-CZ5, SUGITOH),
and a CCD camera (EOS Kiss X7i, Canon). This
subsystem enabled us to observe the surface of thespecimen and examine the particle distribution. The
specimen was placed on a three-dimensional
motorized stage and was irradiated with a pulsed
laser at a desired position of the surface as seen by
the subsystem described above.
Figure 2 describes the two-dimensional

Fig. 1 Block diagram of LIBS setup.
Fig. 2 Two-dimensional distribution of alumina particles inthree types of ferric stainless steels.

distribution of the alumina inclusions by detecting
the ratio of emission intensity of Al I 396.152 nm /CrI 396.369 nm.
In this case, the size of the crater, formed by alaser pulse energy of 50 mJ, was ca. 40 μm. The
measurement time by LIBS for a single spot could
be shortened to within 1 ms. Therefore, the LIBS
technique allows a rapid measurement of distributionof alumina particles on the surface of steels [1].
References[1] S. Nakahata, S. Kashiwakura, and K. Wagatsuma, Surf.
Interface Anal. DOI:10.1002/sia.6217 (2017).

Keywords: laser plasma, spectroscopy
Shunsuke Kashiwakura (Analytical Science Division)
E-mail: shunsuke-k@imr.tohoku.ac.jp
URL: http://wagatsuma.imr.tohoku.ac.jp/

IMR KINKEN Research Highlights 201713

Energy-related Materials

IMR KINKEN Research Highlights 2017

Research

Energy-related Materials

In situ Observation of Twin Boundary Formation at Crystal/
Melt Interface of Multicrystalline Si

Formation mechanism of twin boundary at the grain boundaries in multicrystalline Si was elucidated by in situ
observation of crystal/melt interface during directional solidification. A twin boundary was formed on the {111}facet of a grain-boundary groove at the crystal/melt interface due to a large amount of local undercooling at thegroove.

Multicrystalline Si (mc-Si) ingots, grown by
directional solidification for use in solar cells, always
exhibit twin boundaries. However, the underlying
reason for its occurrence is not well understood.
We attempted to obtain experimental evidences
for the generation of {111} Σ3 twin boundaries at thegrain boundaries during the directional solidificationof mc-Si. The crystal/melt interface of a mc-Si
sample with grain boundaries was observed byusing an in situ observation system that consisted ofa furnace and a microscope. Figure 1 shows acrystal/melt interface of mc-Si in motion. Grooves at
the grain boundaries were observed at the crystal/melt interface. It was confirmed that those grooves
were surrounded by {111} facet planes. The depth of
the groove, as indicated by the red circle, increased
with crystal growth. The melt in this deep groove
then rapidly crystalized, filling the groove. It wasnoted that a new line, indicating the formation of a
new boundary, extended from under the {111} facetthat formed a deep groove. Analysis of the grainboundary characteristics by EBSP confirmed thatthe new boundary, which was generated upon rapid
crystallization at the deep groove, was a Σ3 twinboundary (the bottom image in Fig. 1). The driving
forces for crystallization (undercooling, ΔT) at theflat interface and at the deep groove were estimatedfrom the growth velocities obtained by in situ
observation, and were found to be ΔT ≈ 9.5×10 -5 K
and ΔT ≈ 1.3×10 -3 K, respectively. In general, during
the growth of mc-Si ingots, the temperature gradientis positive in the growth direction, as was observedin the present study. Under these conditions, as thegrain boundary groove deepens the local
undercooling at the groove also increases, asestimated here. As the undercooling, i.e., the driving
forces for crystallization increases, so does theprobability of twin boundary formation.In summary,the formation of grain boundary groove is the causeof twin boundary generation because the {111} facet
planes appear on the crystal/melt interface at thegroove, and the local undercooling of the melt in the
Keywords: crystal growth, solar cells
Kozo Fujiwara (Crystal Physics Division)
E-mail: kozo@imr.tohoku.ac.jp
URL: http://www.xtalphys.imr.tohoku.ac.jp/

16

IMR KINKEN Research Highlights 2017

Fig. 1 (Top) Direct observation of twin boundary formation.
(Bottom) Result of EBSP analysis.

groove becomes large [1].
References[1] K. Fujiwara, R. Maeda, K. Maeda, and H. Morito,
Scripta Matrialia 133, 65 (2017).

IMR KINKEN Research Highlights 2017

Mechanism of Oxygen Segregation at Grain Boundaries in
SiliconOxygen atoms in silicon ingots used for solar cells segregate at bond-centered positions under tensilestresses above ~2 GPa to attain a more stable bonding network by reducing local stresses. The number ofoxygen atoms segregating per unit grain boundary area, NGB (in atoms/nm2), is hypothesized to be proportional
to both the number of the tensile-stressed positions per unit boundary area, nbc, and the average concentrationof oxygen atoms around the boundary, [Oi] (in at%), with NGB~50nbc[Oi].
Grain boundaries (GBs) in Si ingots that areused for solar cells have serious impacts on thesolar cell efficiency owing to the segregation of
detrimental impurity atoms. Impurity atoms such as
oxygen and transition metals are introduced during
crystal growth and cell processing, depending on
the structural conditions at GBs. A precise
understanding of the segregation mechanism is an
important issue for the production of cost-effective
solar cells by engineering the structural condition of
the impurities segregating at GBs.
In the present work, we developed an analyticalmethod to determine the segregation mechanism
on a GB at the same nanoscopic location using
atom probe tomography (APT) and transmission
electron microscopy (TEM). We discuss thesegregation mechanism in terms of bond distortions
around the GB. The three-dimensional distributionof impurity atoms was systematically determined at
typical large-angle GBs (i.e., Σ3{111}, Σ9{221},Σ9{114}, Σ9{111}/{115}, and Σ27{552}) [1, 2] andsmall-angle GBs [2, 3] by APT with a low impurity
detection limit (0.005 at% on a GB plane) and highspatial resolution (approximately 0.4 nm). This wascorrelated with the atomic stresses around GBs
estimated by ab initio calculations based on atomicresolution scanning TEM data (for large-angle GBs[1] (Fig. 1)) and by calculations using the elastic
theory, based on dark-field TEM data (for smallangle GBs [3]). It is hypothesized that oxygen atoms
segregate at the bond-centered positions under
tensile stresses above ~2 GPa to attain more stablebonding networks by reducing the local stresses [1].
The number of segregating atoms per unit GB area
(NGB) is proportional to both the number of stressed
positions per unit GB area (nbc) and the average
concentration of oxygen atoms around the GB ([Oi]),
with NGB~50nbc[Oi]. This indicates that theprobability of finding oxygen atoms at segregation
positions would be, on average, 50 times larger thanthat in bond-centered positions in defect-freeFig. 1 (a, c) Bonding network and (b, d) distribution of
atomic stress Patomic at (a, b) Σ9{221} and (c, d) Σ9{114}
GBs. (e, f) Number of bond-centered positions under atensile stress Pbc above 1.5 GPa and (g, h) oxygen
density across the GB plane for (e, g) Σ9{221} and (f, h)Σ9{114} GBs.

regions. This nanoscopic finding may provide
general guidance to control compositions and band
structures at GBs via oxygen segregation.
References[1] Y. Ohno, K. Inoue, K. Fujiwara, K. Kutsukake, M. Deura, I.
Yonenaga, N. Ebisawa, Y. Shimizu, K. Inoue, Y. Nagai, H.
Yoshida, S. Takeda, S. Tanaka, and M. Kohyama, Appl. Phys.
Lett. 110, 062105 (2017).
[2] Y. Ohno, K. Kutsukake, M. Deura, I. Yonenaga, Y. Shimizu, N.
Ebisawa, K. Inoue, Y. Nagai, H. Yoshida, and S. Takeda, Appl.
Phys. Lett. 109, 142105 (2016).
[3] Y. Ohno, K. Inoue, K. Fujiwara, M. Deura, K. Kutsukake, I.
Yonenaga, Y. Shimizu, K. Inoue, N. Ebisawa, and Y. Nagai,
Appl. Phys. Lett. 106, 251603 (2015).

Keywords: solar cells, grain boundaries
Yutaka Ohno (Physics of Crystal Defects Division)
E-mail: yutakaohno@imr.tohoku.ac.jp
URL: http://lab-defects.imr.tohoku.ac.jp

IMR KINKEN Research Highlights 201717

Energy-related Materials

Molecular Dynamics Simulation for Clean Energy Society
and Super-Precise System

Novel materials design for clean energy and super-precise systems strongly requires a deep understandingof multi-physics phenomena, including chemical reactions, friction, impact, fluid, heat etc. We applied themulti-physics computational simulator we developed based on the molecular dynamics method and revealed
the multi-physics phenomena contributing to the materials design related to the mechanical engineering suchas fuel cell, electronics etc.

High-functionalandhigh-performancematerials are necessary in a wide variety of research
fields such as fuel cell, electronics, tribology, etc.,
for solving the energy and environmental problems
and for the development of super-precision systems.
Currently, a deep understanding of multi-physics
phenomena, including chemical reactions, friction,
impact, fluid, heat etc, is required for materials
design. However, traditional simulation methods
such as first-principles calculations and fluid
mechanics cannot simulate the abovementioned
multi-physics phenomena. Therefore, we applied
our multi-physics simulator based on molecular
dynamics,
tight-binding
quantumchemicalmolecular dynamics, etc., for pioneering nextgeneration materials design [1-2].
The alkaline fuel cell (AFC) has attracted muchattention because it does not require Pt catalysts
owing to its operation in an alkaline environment.
NaxCoO2 is expected to be a promising solid
alkaline electrolyte for AFC. In order to elucidate theion conduction process, we performed ion
conduction simulations for Na0.6(H3O)0.2Co0.94O2,
as shown in Fig. 1 (a), by using the molecular
dynamics method. The results show that OH- ionsand H2O molecules are generated from H3O+
between the CoO2 layers and that H atoms move
between OH - or H2O. The trajectory of H in H3O isshown in Fig. 1 (b), and those of O in H3O and Na
are shown in Fig. 1 (c). The trajectories indicate thatthe movement of H is most prominent. Hence, we
propose the Grotthuss mechanism rather than thevehicle mechanism as the OH - conduction process
in Na0.6(H3O)0.2Co0.94O2 for the electrolyte [1].
Chemical mechanical polishing (CMP) is
required to produce a nondefective and atomicallyplanar Cu surface for miniaturized semiconductor
chips. In order to understand the Cu CMP process,we performed a CMP simulation on a Cu(111)
surface polished with a SiO2 abrasive grain underaqueous H2O2. In aqueous H2O2, O atoms adsorbedon the nascent Cu surface are generated by thechemical reactions of H2O2 molecules. Additionally,(a) Co

IMR KINKEN Research Highlights 2017(c)trajectory of O

O(H3O) trajectory of H trajectory of Na

Na H

Fig. 1 (a) Model of Na0.6(H3O)0.2Co0.94O2. Trajectories of(b) H in H3O, (c) O in H3O and Na between the CoO2
layers.
(a)

Load

H
SlidingSi(b)

SiO2 abrasive
grain

H2O2

O
H2O

Cu(111)Cu

0.0 psRaised Cu
Intrusionof O

41.1 ps

Fig. 2 Snapshots of Cu CMP simulation by a SiO2 abrasive
grain under aqueous H2O2 at (a) 0 and (b) 41.1 ps.

friction by the abrasive grain causes the intrusion of
the adsorbed oxygen atom into the Cu bulk (Fig. 2(b)). We reveal that this intrusion of the surfaceadsorbed O atom is the most important process forthe efficient polishing of the Cu surface because it
induces the dissociation of the Cu−Cu backbonds
and raises Cu atoms that are sheared off andremoved by the abrasive grain [2].
References[1] K. Kato, H. Kasai, A. Hori, M. Takata, H. Tanaka, S. Kitagawa,A. Kobayashi, N. Ozawa, M. Kubo, H. Arikawa, T. Takeguchi,
M. Sadakiyo, and M. Yamauchi, Chem. - An Asian J. 11, 1537
(2016).
[2] K. Kawaguchi, H. Ito, T. Kuwahara, Y. Higuchi, N. Ozawa, and
M. Kubo, ACS Appl. Mater. Interfaces 8, 11830 (2016).

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

18

O(CoO2) (b)IMR KINKEN Research Highlights 2017

Modeling of One-Dimensional Migration of Self-Interstitial
Atom ClustersMechanisms of one-dimensional migration of self-interstitial atom clusters were studied using in situ
observation under electron irradiation and atomistic simulations. We proposed that one-dimensional migrationin iron was interrupted by impurity atoms at high temperatures and by vacancies accumulated at highconcentrations under irradiation at low temperatures.
Fe2, 1250 kV, 0.01 dpa s-1

100

300 K

number of counts

10

100

200 K

100

100

10

1

150 K

10

100

10

250 K

10

110 K
0

20

40

60

1D migration distance (nm)Fig. 1 Irradiation temperature dependence of experimental
1D migration distance of SIA clusters observed in ironat 1250 kV.
250

total interaction energy, u

Self-interstitial atom (SIA) clusters perform onedimensional (1D) migration, i.e., a gliding motion
along the Burgers vector with low activation energy.
In a recent theory on defect structural evolution
under high-energy neutron irradiation, 1D migrationis regarded as a potential mechanism for controllingthe kinetics of the defect reactions: e.g., void
swelling and heterogeneous defect distribution neardislocations and grain boundaries. 1D migration istherefore of practical and fundamental importancein relation to nuclear materials research.
We conducted in situ observation of 1D
migration of SIA clusters in iron under electron
irradiation at 110–300 K using high-voltage electron
microscopy. Most of the 1D migration was stepwise
positional changes of the SIA clusters at irregulartime intervals at all temperatures. The frequency of
1D migration was independent of the irradiation
temperature and was directly proportional to thedamage rate, suggesting that 1D migration was
induced by electron irradiation. In contrast, the 1D
migration distance depended on the temperature:
distribution of the distance ranged over 100 nm
above 250 K, decreased steeply between 250 and
150 K, and was less than 20 nm below 150 K. The
distance above 250 K corresponded to that of thefree path of SIA clusters gliding through impurity
atoms, suggesting that impurity atoms act as traps
for SIA clusters [1,2]. However, the steep decreasein 1D migration distance at low temperatures could
not be explained by the impurity effect.
Next, we examined the fluctuation in theinteraction energy between an SIA cluster and thevacancies of random distribution at concentrations of
10 -4 –10 -2 using molecular statics (MS) simulations.
The fluctuation trapped SIA clusters with 4 nm
diameter at vacancy concentrations higher than 10 -3.
We proposed that 1D migration was interrupted by
the vacancies accumulated at high concentration
under electron irradiation at low temperatures,
where the vacancies are not thermally mobile [3].

(nm)
260

Cv=10-4

0.25 eV

Cv=3x10-3

0.25 eV

Cv=10-3

0.5 eVCv=3x10-2

1 eV

Cv=10-2

1000

270

1 eV

1100

1D migration distance (b)Fig. 2 Vacancy concentration dependence of totalinteraction energy of a 217-SIA cluster gliding throughvacancies of random distribution estimated with the MS
method.

References[1] Y. Satoh, H. Matsui, T. Hamaoka, Phys. Rev. B77, 94135(2008).
[2] Y. Satoh and H. Matsui, Philos. Mag. 89, 1489 (2009).
[3] Y. Satoh, Y. Abe, H. Abe, Y. Matsukawa, S. Kano, S. Ohnuki,
and N. Hashimoto, Philos. Mag. 96, 2219 (2016).

Keywords: nuclear materials, electron irradiation, simulation
Yuhki Satoh (Nuclear Materials Engineering Division)
E-mail: ysatoh@imr.tohoku.ac.jp
URL: http://nuclmater.imr.tohoku.ac.jp/index.html

IMR KINKEN Research Highlights 201719

Energy-related Materials

Evolution of a Bicontinuous Nanostructure via a Solid-State
Interfacial Dealloying ReactionLiquid metal dealloying (LMD) is an attractive method for the fabrication of nano/micro porous metals. However,there is simultaneous and remarkable growth of ligaments due to the diffusion of thermally activated atoms.
Recently, we have developed an interconnected Fe-Cr alloy with a ligament width below 200 nm by a solidstate dealloying reaction using (Fe,Cr)-Ni and Mg diffusion couples. A nanofilament structure in the solid-state
reaction interface revealed that the interfacial spinodal decomposition and diffusion-coupled growth occurredat the dealloying front.
Dealloying in aqueous solution is a promising
method for the production of three-dimensional
nanoporous structures, but its application is limited
to noble metals. LMD, which has been newly
proposed by our group, overcomes the above
limitation [1]. During LMD, a component is selectively
dissolved in a metallic melt depending on the
miscibility among the atoms. Although LMD has theadvantage of a high reaction rate, a coarsening
phenomenon is unavoidable due to hightemperatures.
The present work investigates the dealloying
reaction using a dealloying metal bath, which is in
the solid state (Fig. 1(a)) [2]. Fig. 1(b) shows theinterfacial structure of the diffusion couple. After theetching treatment, a bundle of ordered nanofilamentswith width below 100 nm and length of some microns
could be extracted near the dealloying front, asshown in Fig. 1(c). The electron diffraction patterns
confirm that these filaments have a body-centeredcubic structure. In addition, the four diffraction
patterns (No. 1-4 in Fig. 1(c)) obtained for a single
filament indicate that the filament grows as a single
crystal. These filaments are intermediate productsthat develop into a bicontinuous topology from thedense precursors by losing Ni. At an early stage ofdealloying, the chemical composition of thedealloying front became unstable, resulting in phaseseparation. The separated solid nanoscale islands
grew cooperatively, with the liquid phase penetrating
the precursor, forming nanosized solid lamellae/
filaments between the liquid channels.
The interconnected structure with a ligament
width below 200 nm was homogeneously distributedin the rest of the reaction layer (Fig. 1(d)). The lowtemperature hindered atomic diffusion, thus
producing a much finer porous structure than thatobtained by LMD. Electron diffraction performed at
two different points of the same ligament exhibited
two distinct patterns. Therefore, the interconnected
Keywords: nanostructure, foam, porosity
Hidemi Kato (Non-Equilibrium Materials Division)
E-mail: hikato@imr.tohoku.ac.jp
URL: http://www.nem.imr.tohoku.ac.jp

20

IMR KINKEN Research Highlights 2017

Fig. 1 (a) Schematic illustration of a solid-state interfacial
dealloying reaction. (b) SEM micrograph of theinterfacial structure. (c) TEM image and electron
diffraction patterns of the dealloying front. (d)Interconnected nanoporous structure.

porous structure is considered as connectedparticles with different crystal orientations.
The structure is likely formed by the bonding of
deflected filaments or broken fragments at the tipsof the filaments. The average composition of thefabricated nanoporous metal was Fe80.7Cr18.6Ni0.7
at%, indicating that the solid-state dealloying
reaction was feasible even at low temperatures. It is
worth noting that the ligament size of the porous
metal was about one order of magnitude finer thanthat prepared in Mg melt at its melting temperature.
References[1] T. Wada, K. Yubuta, A. Inoue, and H. Kato, Mater. Lett. 65, 652(2011).
[2] T. Wada, K. Yubuta, and H. Kato, Scripta Mater. 118, 33 (2016).

IMR KINKEN Research Highlights 2017

Extending the Applicability of the Goldschmidt Tolerance
Factor to Arbitrary Ionic CompoundsCrystal structure determination for new compounds with light elements such as hydrides is challenging. Thus,
we introduce the concept of ionic filling fraction (IFF) based on the occupancy of constituent ions in a crystal
structure. IFF revealed that the ionic compounds are linearly arranged. The linearity can guide towards a
suitable unit cell and composition for novel compounds. Using IFF, we could determine the crystal structuresof new hydrides as potential high-density hydrogen storage materials.
The Goldschmidt tolerance factor (T) of
perovskite compounds is used to evaluate theperovskite-type structures in terms of ionic packing.
However, since its applicability is limited to only
perovskite compounds, a description of crystal
structures of other compounds using this factor isunobtainable. In particular, hydrides, which are
regarded as energy related materials, occur in an
extensive variety of chemically and structurally
diverse compounds due to the high reactivity ofhydrogen [1, 2].
Herein, we present a first report on the possibilityof extending the applicability of T to ionic compoundswith arbitrary ionic arrangements and compositions
including hydrides [3]. In order to extend theapplicability, we focused on the occupancy of theconstituent spherical ions in their crystal structures.
We referred to it as the ionic filling fraction (IFF),
which is derived from the volume ratio between the
crystal structure (Vunit) and the total constituent ions
(Vion) (Fig. 1). The ionic compounds including
perovskite
compounds
showedalineararrangement, based on the IFF (Fig. 2), which wasconsistent with T.
Furthermore, the linearity could suggest
suitable crystal structures (unit cell) and composition
ratio for novel compounds, thus addressing one of
the biggest bottlenecks in the process of crystal
structure determination.
Using IFF, we could successfully elucidate thecrystal structures of new hydrides [3], corresponding
to potentially high-density hydrogen storage
materials with complicated crystal structures andcompositions. We could therefore prove from apractical point of view that the IFF concept can
extend the applicability of T to arbitrary ioniccompounds and facilitate the determination of
crystal structures with arbitrary ionic arrangements
and compositional ratios.

Fig. 1 Concept of IFF in an ideal cubic perovskite structure(purple sphere: A; lime spheres: B; black spheres: X;
grey cuboid: Vunit /Z (Z = 1); purple+lime+3×black
spheres: Vion).

Fig. 2 IFF plot for ionic compounds with arbitrary ionicarrangements and compositions. IFFs for 136 ioniccompounds are shown (black line: Vunit /Z = 1/0.69×Vion(IFF = 0.69); grey dot curve: T = 1.0). Inset shows acrystal structure of a new hydride LiCa(AlH4)3
determined by the IFF.

References[1] S. Orimo, Y. Nakamori, J. R. Eliseo, A. Züttel, and C. M.
Jensen, Chem. Rev. 107, 4111 (2007).
[2] S. Takagi and S. Orimo, Scripta Mater. 109, 1 (2015).
[3] T. Sato, S. Takagi, S. Deledda, B. C. Hauback, and S. Orimo,
Sci. Rep. 6, 23592 (2016).

Keywords: energy storage, Goldschmidt tolerance factor, hydride
Toyoto Sato and Shin-ichi Orimo (Hydrogen Functional Materials Division)
E-mail: toyoto@imr.tohoku.ac.jp and orimo@imr.tohoku.ac.jp
URL: http://www.hydrogen.imr.tohoku.ac.jp/en/index.html

IMR KINKEN Research Highlights 201721

Energy-related Materials

High-speed Growth of Na-β-Alumina Crystalline Films by
Laser Chemical Vapor DepositionS

odium-beta-alumina (Na-β-alumina) has a high ionic conductivity, and is thus used as a solid electrolyte in
Na-S batteries. However, Na-β-alumina crystalline films have been hardly synthesized because of its highprocess temperature and high volatility. We demonstrate the growth of Na-β-alumina crystalline films at highdeposition rates by laser chemical vapor deposition.
Na-β-alumina is best known for its fast ionic
conductivity and negligible electronic conductivity.
It is typically synthesized in bulk by solid statesintering at temperatures above 1873 K, being
widely used for high-power sodium (Na)–Sulphur(S) batteries. Although the doping of alkali andalkaline earth metals such as Li+, K+, and Mg2+
stabilizes the structure of β-alumina at low
temperatures, the synthesis of Li+/Mg2+-doped Naβ-alumina films often requires high temperatures
above 1573 K, which result in the loss of alkali andalkaline earth metals. While amorphous films withthe corresponding compositions can be fabricatedat relatively low process temperatures by various
methods, the synthesis of Na-β-alumina crystalline
films with high ionic conductivity have been rarely
reported.
Laser chemical vapor deposition (CVD) is
greatly advantageous for the growth of films withalkali-containing materials because the deposition
reactions can be selectively accelerated around thesubstrate by laser irradiation with minimal loss of Na[1]. We successfully synthesized Na-β-alumina films
by laser CVD using metal-organic Al and Na
precursors. The Na-β-alumina film at the deposition
temperature of 1345 K comprised flake-like grains
grown in random directions (Fig. 1(a)) [2, 3]. The
flake-like grains were elongated from the substrate,
where the (0001) planes of the Na-β-alumina wereinclined from the substrate surface (Fig. 1(b)). The
maximum deposition rate was 44 μm.h−1.
It is well known that the βʹʹ-phase exhibits ahigher ionic conductivity than does the β-phase. In
our work, the Li-doped Na-β/βʹʹ-alumina films weregrown by laser CVD at deposition temperatures of1120–1200 K, which were 100–200 K lower thanthose for Na-β-alumina [4].
The Li-doped alumina film was composed ofaggregated faceted grains (Fig. 2(a)), and theelectron diffraction pattern indicated the coexistenceof β and βʹʹ phases. The deposition rate of the Na-β/βʹʹ-alumina film was 60 µm·h−1.

Fig. 1 Microstructure of Na- β-alumina film prepared bylaser CVD. (a) SEM surface image and (b) crosssectional TEM bright field image.

Fig. 2 (a) Cross-sectional TEM bright field image and (b)selected area electron diffraction pattern of Li-doped
Na-β/βʹʹ-alumina films prepared by laser CVD.

References[1] C. Chi, H. Katsui, R. Tu, and T. Goto, J. Ceram. Soc. Jpn. 124,
111 (2016).
[2] C. Chi, H. Katsui, and T. Goto, Surf. Coat. Technol. 276, 534(2016).
[3] C. Chi, H. Katsui, and T. Goto, J. Wuhan University ofTechnology-Mater. Sci. Ed. 31, 6 (2016).
[4] C. Chi, H. Katsui, and T. Goto, Ceram. Int. 43, 1278 (2017).

Keywords: chemical vapor deposition, ionic conductor, microstructure
Hirokazu Katsui (Creation of Life Innovation Materials for Interdisciplinary and International Researcher Development)
E-mail: katsui@imr.tohoku.ac.jp
URL: http://life-pro.imr.tohoku.ac.jp

22

IMR KINKEN Research Highlights 2017

IMR KINKEN Research Highlights 2017

“Infinite Fluctuation” in Two-Dimensional Glass and theModality of Its Slow RelaxationProfessional development Consortium for Computational Materials Scientists (PCoMS) supports and develops
the young researchers of computational materials science with a broader view and extensive knowledge ofinterdisciplinary materials science, condensed matter physics, molecular science, and materials design fromfundamental researches to applications. Introduced bellow is a recent activity by key members of PCoMS.
Novel glassy fluctuation in two-dimensional system is revealed from their investigation of the relaxation process
and system-size effect in a low-dimensional glass former by using large-scale computer simulations.
Since heterogeneous dynamics associatedwith slow relaxation in supercooled liquids andstructural glasses were discovered about twenty
years ago, much effort has been devoted to theunderstanding of its nature. Its relevance tomechanical and thermal properties is one of the hot
topics in the materials and physical sciences ofmetallic glasses and soft materials.
Our recent numerical simulation of a glassforming liquid in lower-dimensional space revealed
a novel type of glassy fluctuation [1]. We havesimulated large-scale dynamics of two-dimensional(2D) and three-dimensional (3D) model systems offragile glass formers by using supercomputers.
While the 3D system exhibits the usual caged
vibration, in the 2D system, cooperative vibration isenhanced by the long-wavelength acoustic
vibrations. Because glassy liquids and amorphoussolids lack the crystalline order parameter, suchproperties can be recognized only by examining the
dynamical quantities including the mean-squaredisplacements and self-correlation functions. The
enhanced vibration stems from the origin that iscommon with that of the 2D crystalline solids, i.e.,
Mermin-Wagner theorem.
The standard spatiotemporal correlation
functions based on the density field description failto characterize the relaxation as the coherent motion
is involved in the 2D system due to the longwavelength vibrations. In our study [1], we further
defined other dynamic susceptibilities and dynamic
correlation lengths based on the bond-breakage
function [2], which is an indicator not for the simple
displacement but for the local structural relaxation.
Herewith, we could evaluate the glassy structural
relaxation of a 2D glassy liquid, separating out theinfinite fluctuation that adds behaviors dependent
on the length scales.
This work provides a new possible guiding

Fig. 1 Modality of the glassy vibrational fluctuation is
illustrated for 2D and 3D systems. In a 3D system, aparticle vibrates in a cage formed by its surrounding
particles under the densely packed condition, andintermittently goes out of the cage (left figure). In a 2D
system, long-wavelength vibrational waves induce acollective motion of particles. The range of vibration
motion can exceed the length scale of particle radii,
which is illustrated by an aqua colored circle (rightfigure).

principle for the understanding of long-wavelength
fluctuations in low-dimensional systems. This study
indicates efficient transfer of sound vibrations inpurely 2D glassy materials, which might possibly be
useful for the forthcoming energy-saving societies.
This 2D-specific fluctuation is commonly expectedin 2D materials composed of colloids, superfluid
vortex, and other strongly correlated systems. The
fundamental nature of a 2D glass transition could
still be affected by the infinitely growing fluctuation,
which is left for future investigations.
References[1] H. Shiba, Y. Yamada, T. Kawasaki, and K. Kim, Phys. Rev. Lett.
117, 245701 (2016).
[2] H. Shiba, T. Kawasaki, and A. Onuki, Phys. Rev. E 86, 041504(2012).

Keywords: amorphous, mechanical properties, simulation
Hayato Shiba (Professional development Consortium for Computational Materials Scientists)
E-mail: shiba@imr.tohoku.ac.jp
URL: http://www.imr.tohoku.ac.jp/~shiba/
Tetsuo Mohri (Project Leader of Professional development Consortium for Computational Materials Scientists)

IMR KINKEN Research Highlights 201723

Electronic Materials

IMR KINKEN Research Highlights 2017

ResearchElectronic Materials

Electric Charge Localized on Magnetic Domain Walls in
Weyl Semimetals

Efficient manipulation of magnetic domain walls is essential for their applications as information carriers in

spintronics devices. Here, we demonstrate the electric charging of domain walls in Weyl semimetals by
analytical and numerical calculations, which may enable control of the domain wall motion by external electricfields without Joule heating.

Keywords: Weyl semimetal, domain wall, spintronics
Yasufumi Araki (Theory of Solid State Physics Division)
E-mail: araki@imr.tohoku.ac.jp
URL: http://www.bauer-lab.imr.tohoku.ac.jp/?page=&lang=en

26

IMR KINKEN Research Highlights 2017

charge distribution (a.u.)electric fieldE

0.000012

driving force QE
chargeQ

Fig. 1 (top) Analytically obtained charge distribution aroundthe magnetic DW. An external electric field induces adriving force on the DW. (bottom) A schematic spin
texture of a coplanar-type DW.
3.2×10-3

coplanarspiralhead to head

2.4×10-3δρa3/eWeyl semimetals form a class of topologicalmaterials showing intermediate characteristics
between metals and insulators; they arecharacterized by isolated band-touching points(Weyl points) in the Brillouin zone around which theband dispersion is linear in three dimensions. Its
realization requires a strong atomic spin-orbit
coupling, giving rise to a strong correlation between
the electron spin and momentum. Such spinmomentum locking feature leads to the expectationthat topological magnetic textures in Weyl
semimetals would give rise to nontrivial electronic
properties.
We theoretically addressed the electronic
properties of Weyl semimetals by both analytical [1]and numerical [2] methods, in the presence of amagnetic domain wall (DW) formed by localized
magnetic moments distributed in the sample. The
eigenstates of the system were obtained by exactly
diagonalizing the Weyl Hamiltonian, revealing afamily of zero modes bound to the DW. The boundstates can be regarded as the zeroth Landau levels
induced by the fictitious “axial” magnetic fieldcorresponding to the magnetic texture of the DW.
They give rise to a certain amount of electric charge
localized at the DW (see Fig. 1), which can be tunedby the overall chemical potential and is independentof the width of the DW. The emergence of thelocalized charge is related to the zeroth Landaulevels and is topologically robust. Moreover, theamount of the localized charge depends on thetype of DW texture, as is evident from the plot in Fig.
2.
Electric charging of the DW implies that the
motion of the DWs in Weyl semimetals can be
manipulated by external electric fields. Since the
DW is opaque for electric currents due to themismatch of the electron helicity, the electrostaticforce on the localized charge is the only driving
force that can induce DW motion without Joule
heating. An electric field around 10-100 V/cm isrequired to drive the DW motion at a speed of 10-

1.6×10-3

0.8×10-3

0

-0.5

-0.25

0

0.25

0.5

z/L
Fig. 2 Numerically obtained charge distributions aroundthree types of DW textures: coplanar, spiral, and headto-head.

100 m/s. We expect that such an efficient control ofmagnetic DWs will introduce new strategies forhigh-performance information storage technologies
such as magnetic racetrack memories.
References[1] Y. Araki, A. Yoshida, and K. Nomura, Phys. Rev. B 94, 115312(2016).
[2] A. Yoshida, Y. Araki, and K. Nomura, paper in preparation.

IMR KINKEN Research Highlights 2017

Neutron and X-ray Scatterings under Extremely Strong
Magnetic Fields

Mobile pulsed field generator has been used to investigate magnetic and crystal structures as well as

magnetic and electronic states of various strongly correlated electron systems including Cu-oxide
superconductors, multiferroics, and intermetallics. It enables us to access unique information by the combinationof intense beam sources with strong magnetic fields.

A high magnetic field induces new states ofmatters by its strong coupling with the spin andcharge degrees of freedoms of an electron. To
unveil such states, the use of neutron and X-ray
scatterings is indispensable. We have developed amobile pulsed field generator to realize the neutronand x-ray scattering experiments in very strong
magnetic fields in the range of 20-50 T.
Figure 1 shows the mobile capacitor bankdesigned and assembled at IMR. It stores 16 kJ ofenergy and can drive different types of mini coils for
X-ray spectroscopies and X-ray diffraction. The
magnet for neutron diffraction is also shown. The
power supply and the magnet have been used forvarious experiments in domestic and oversea
facilities.
One of the recent highlights is the observationof unidirectional and three-dimensionally correlated
charge density wave (CDW) in magnetic fields
above the upper critical field. The observation
clearly indicates that the ground state of YBCO
superconductor around a hole concentration of 1/8
and a magnetic field above the critical field is the
CDW state [1].
From neutron diffraction, we found an
incommensurate density wave-like magnetic
ordering in the high magnetic field phase of URu2Si2.
This compound has been of interest for many years
due to the appearance of the mysterious hidden
order phase, where no clear order parameter has
been identified, although the evidence of phasetransition is shown by macroscopic parameterssuch as heat capacity. The observation of theincommensurate order indicates that the magnetictransition is closely related to the change in the
Fermi surface [2].
The pulsed magnet has been also used to
explore an unknown elementary particle calledaxion, which is believed to be responsible for thedark matter in space. In a high magnetic field, thephoton is converted to axion with a higher efficiency.
By collaborating with a Tokyo University group, we

Fig. 1 The mobile pulsed field generator and the magnet
used for neutron diffraction.

have extended the boundary where the axion isabsent. As such, the combination of strong magnetic
fields and scattering techniques opened up a newarea in both condensed matter and fundamental
physics [3].
References[1] H. Jan et al. PNCS 113, 12849 (2016).
[2] W. Knafo Jan et al. Nat. Commun. 7, 13075 (2016).
[3] T. Inada et al. Phys. Rev. Lett. 118, 071803 (2017).

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

IMR KINKEN Research Highlights 201727

Electronic Materials

Spin Currents in a One-Dimensional Quantum Spin LiquidIn quantum spin liquid (QSL), quantum fluctuation disturbs the magnetic ordering while retaining the spincorrelation. Here, we show that a QSL in a spin chain conveys spin currents via its long-range spin correlation.
The result shows that the spin currents flow even in an atomic channel owing to the spin liquid state, and may
thus find application as atomic spin-current wiring in future spintronics.

Keywords: spintronics, quantum spin system, magnetic
Daichi Hirobe (Surface and Interface Research Division)
E-mail: daichi.kinken@imr.tohoku.ac.jp
URL: http://saitoh.imr.tohoku.ac.jp/

28

IMR KINKEN Research Highlights 2017

BaHeat bath
Sr 2CuO3

c

b

ѭT
Pt
20
Pt/MgO

10
0

8

-10

4

〜

V/B (nV/T・K)

The flow of electron spins is termed as spincurrent. In spintronics, finding materials that carryspin current efficiently is crucial, especially for
integrated microscopic devices. To date, two typesof spin currents, conduction-electron and spin-wave
spin currents, have been explored experimentally.
The former is mediated by the motion of electrons inmetals and semiconductors, while in the latter, thespin waves carry spin angular momentum even in
insulators.
In a recent paper [1], we reported theobservation of spin currents in one-dimensional (1D)
QSL, which may provide an atomic channel for spintransmission free from magnetic crosstalk. 1D QSL
is realized in 1D spin-1/2 chains, and the archetypeis found in the insulator Sr2CuO3. In this material, thefluctuation of the spins of Cu2+ is so strong that it
prevents magnetic ordering and creates aparamagnetic state with strong spin-singlet
correlation. This correlation gives rise to unusual
magnetic and thermal properties of Sr2CuO3, which
can be highly accurately described by the 1D QSLmodel.
To drive spin currents through the spin chains,
we used a spin Seebeck effect [2], which refers to
the generation of spin currents from a temperature
gradient in the magnets. Figure 1 shows thetemperature dependence of the voltage measured
in a Pt film fabricated on Sr2CuO3. Pt is used as a
spin-current detector based on the inverse spin Hall
effect in which the spin current injected from
Sr2CuO3 is converted into an electromotive force. A
negative voltage signal is clearly observed at low
temperatures. It contrasts markedly with the positive
one due to the thermoelectric effect of Pt. This
unusual negative component was undoubtedly
traced back to the spin currents conveyed through1D QSL by the control experiments as well as a
microscopic theory for the spin Seebeck effect.
Recently, optically induced crystallization of
amorphous Sr-Cu-O was developed by otherresearch groups, wherein the spin-chain directionsaligned along the light-scanning direction. In-20

Pt/Sr2CuO3

0
-4
-8

-30
0

100

100 150 200 250 300

200

300

T (K)
Fig. 1 (top) Schematic illustration of the experimental setup. A temperature gradient was generated along thespin chains. (bottom) Temperature dependence of thevoltage measured in Pt/Sr2CuO3 (blue). Voltage signals
solely due to the thermoelectric effect of Pt are alsopresented for comparison (grey). Sign reversal around180 K, indicated by the red arrow, is attributed to thecompetition between the voltages generated due to thespin currents injected from Sr2CuO3 and thethermoelectric effect of Pt.

addition, the zero excitation gap of 1D QSL wasquite robust against magnetic anisotropy. These
results suggest potential applications of QSL for
tailor-made spin wiring.
References[1] D. Hirobe, M. Sato, T. Kawamata, Y. Shiomi, K. Uchida, R.
Iguchi, Y. Koike, S. Maekawa, and E. Saitoh, Nat. Phys. 13, 30(2017).
[2] K. Uchida, S. Takahashi, K. Harii, J. Ieda, W. Koshibae, K.
Ando, S. Maekawa, and E. Saitoh, Nature 455, 778 (2008).

IMR KINKEN Research Highlights 2017

Transparent Electronics Envisioned with a Highly Mobile
Oxide

T

ransparent conducting oxides (TCOs) possessing high electrical conductivity and optical transparency are
becoming increasingly important as a key component in electronics. Their continuous development hinges on
the materials that can exhibit such properties without relying on indium, which is scarce in the Earth’s crust. In
this work, we attempted to introduce a new TCO candidate, BaSnO3, into thin film research by fabricating highquality epitaxial films and heterointerfaces. The successful improvement in electron mobility of the thin film andtransistor operation shows the potential of this oxide as a new electronic material.

(a)

(b)
Ba
O

Sn

1 µm

a = 4.116 Å100
2 -1 -1

Mobility (cm V s )With the rapid evolution of flat panel displays
and optoelectronic devices, there has been an
increasing demand for new TCOs that can replace
the widely used indium-tin oxide. A perovskitestannate, BaSnO3 (Fig. 1(a)), has recently emerged
as a candidate owing to its high electron mobility
exceeding 300 cm2V−1s−1 in a single-crystal form,
which obviates the use of costly indium [1,2]. In
addition, the perovskite framework, common to many
oxides, potentially combines high mobility withferroelectricity and ferromagnetism, and controls
dimensionality, leading to conceptually new devices.
However, the large lattice mismatch with thecommercially available SrTiO3 substrate has hindered
the fabrication of high-quality BaSnO3 films.
To mitigate the lattice mismatch, we inserted abuffer layer of an intermediate compound
Sr0.5Ba0.5SnO3 between the BaSnO3 and SrTiO3
substrates. We obtained an atomically smooth
BaSnO3 surface after post annealing, as shown in
Fig. 1(b) [3]. La-doped BaSnO3 TCO films on
buffered BaSnO3 showed a marked enhancement
in mobility as compared with that of the non-bufferedfilms (Fig. 1(c)). Based on cross-sectionaltransmission electron microscopy observation, we
attributed this to the reduced number of misfit
dislocations and the resulting suppression ofelectron scattering.
We also demonstrated successful field-effecttransistor operation using the insulating, bufferedBaSnO3 film as the channel [4]. Moreover, we foundthat modulating the interface band profile byfabricating a heterostructured channel withovergrown wide-gap Sr0.5Ba0.5SnO3 barrier layer
effectively enhanced the transistor characteristics.
These results clearly demonstrate the criticalimportance of well-defined surface and sharp
interface in outstripping the existing TCOs with
BaSnO3.

(c)on buffered BaSnO3

80
60
40
20
0
0

on SrTiO3
5 mm

La0.02Ba0.98SnO3

100
200
Temperature (K)300

Fig. 1 (a) Crystal structure of BaSnO3. (b) Atomic force
microscopy surface image of the annealed BaSnO3/
Sr0.5Ba0.5SnO3/SrTiO3. (c) Hall mobility of La0.02Ba0.98SnO3transparent conducting films on BaSnO3/Sr0.5Ba0.5SnO3/
SrTiO3 and SrTiO3 as a function of temperature. Inset:
optical image.

References[1] H. J. Kim, U. Kim, H. M. Kim, T. H. Kim, H. S. Mun, B.-G. Jeon,
K. T. Hong, W.-J. Lee, C. Ju, K. H. Kim, and K. Char, Appl.
Phys. Express 5, 061102 (2012).
[2] S. Ismail-Beigi, F. J. Walker, S.-W. Cheong, K. M. Rabe, and C.
H. Ahn, APL Mater. 3, 062510 (2015).
[3] J. Shiogai, K. Nishihara, K. Sato, and A. Tsukazaki, AIP Adv. 6,065305 (2016).
[4] K. Fujiwara, K. Nishihara, J. Shiogai, and A. Tsukazaki, AIP
Adv. 6, 085014 (2016).

Keywords: oxide, thin films, field-effect transistor
Kohei Fujiwara and Junichi Shiogai (Low Temperature Physics Division)
E-mail: kfujiwara@imr.tohoku.ac.jp, junichi.shiogai@imr.tohoku.ac.jp
URL: http://mu.imr.tohoku.ac.jp/index_en.html

IMR KINKEN Research Highlights 201729

Electronic Materials

Critical Elasticity at the Mott Transition in an Organic
Conductor

E

lectrons embedded in a crystal lattice experience mutual Coulomb repulsion, which hinders the flow ofelectrons and changes the metallic system into the Mott insulating state. We have found non-linear lattice
expansion across the Mott transition in an organic conductor. Stronger non-linearity appeared close to the Mott
critical endpoint, highlighting a breakdown of the Hooke’s law of elasticity of the critical electronic system
coupled to the lattice degrees of freedom.
The Mott metal-insulator transition, a paradigmof strong electron-electron correlations as depicted
in Fig. 1, is considered as a source of intriguing
phenomena. Despite its importance for a wide
range of materials, fundamental aspects of thetransition, such as its universal properties, are still
under debate.
We
haverecently
reporteddetailed
measurements of relative length changes as afunction of continuously controlled helium-gas
pressure for the organic conductor κ-(BEDTTTF)2Cu[N(CN)2]Cl across the pressure-induced
Mott transition [1]. Strongly nonlinear variations of
the lattice expansion around the Mott critical
endpoint was observed, highlighting a breakdownof Hooke’s law of elasticity (Fig. 2). These nonlinear
strain-stress relations indicate an intimate, nonperturbative coupling of the critical electronicsystem to the lattice degrees of freedom. Our results
are fully consistent with mean-field criticality
predicted for electrons in a compressible lattice withfinite shear moduli. We argue that the Mott transition
for all systems that are amenable to pressure tuningshows the universal properties of an isostructuralsolid-solid transition.

Fig. 1 Electrons embedded in a crystal lattice - thecomponents of a solid. The electrons avoid being close
to each other because of their mutual Coulomb repulsion,
which hinders the flow of electrons and makes themetallic system insulating.

Fig. 2 Generic temperature-pressure phase diagram
predicted for the Mott metal-insulator transition. The redsolid line represents the first-order transition line that
ends in a second-order critical endpoint. The Widom line
(red dotted line) corresponds to a smooth extrapolationof the first-order line. Blue broken lines (blue-shadedarea) represent the predicted crossover lines (crossover
regime) that emanate from the critical endpoint. In a
distinct region around the critical endpoint, criticalelasticity with mean-field behavior is expected (yellow
circle). Further away from the endpoint (light blue circle),
within a radius given by the Ginzburg criterion, nontrivial
critical exponents of the Mott transition prevail. Outsideof this range (white area), the critical properties can be
described by a mean-field theory. The pink-shaded area
indicates the finite width of the first-order transition due tothe presence of some disorder in real systems.

References[1] E. Gati, M. Garst, R.S. Manna, U. Tutsch, B. Wolf, L. Bartosch,
H. Schubert, T. Sasaki, J.A. Schlueter, and M. Lang, Science
Advances 2, e1601646 (2016).

Keywords: metal-insulator transition, electrical properties, organic
Takahiko Sasaki (Low Temperature Condensed State Physics Division)
E-mail: takahiko@imr.tohoku.ac.jp
URL: http://cond-phys.imr.tohoku.ac.jp/index_e.html

30

IMR KINKEN Research Highlights 2017

IMR KINKEN Research Highlights 2017

Unusually Complex Metamagnetic Behaviors in theNoncentrosymmetric Weak Ferromagnet CePdSi3

In heavy fermion systems, the effects of parity symmetry breaking possibly result in the emergence of novel
superconducting and magnetic properties. We have successfully grown singlecrystalline samples of thenoncentrosymmetric cerium-based compound, CePdSi3, and found considerably interesting metamagnetic
behaviors.
In heavy fermion physics, the effects of the lackof parity symmetry in crystals, as well as themagnetic quantum critical phenomena have attracted much interest as a key to understanding theanomalous superconducting behaviors observed in
CeTSi3 systems (T = transition metal) [1]. In
noncentrosymmetric (NCS) systems, a finite
antisymmetric spin-orbit coupling allows the
admixtureofspin-singlet
andspin-triplet
superconducting state and possibly brings aboutnovel superconducting and magnetic behaviors.
Nevertheless, it seems that parity symmetry
breaking (PSB) is not a necessary and sufficientcondition for the emergence of anomalous
superconductivity and magnetism. In this context,
as is evident from the comparison between Ce(4f 1)
and La(4f 0) compounds, 4f electrons probably playa crucial role in the anomalous behaviors observedin those systems.
For conventional NCS insulating magnets, themagnetic properties can be described with a simple
effective Hamiltonian modified by a DM typeinteraction. On the other hand, in an NCS heavy
fermion system, the RKKY type long-range
interaction and the Kondo effect will render themagnetic properties more complicated and diverse. Even when we focus only on magnetism, ourunderstanding of the effects of PSB in 4f electron
systems is still lacking. Here, we examine such PSB
effects in the NCS CePdSi3. In this compound, the4f electrons are rather localized [1] compared withthose of the other Ce-TSi3 systems, such that it may
be easier to understand the PSB effects on the
4f-electron magnetism.
Singlecrystalline samples of CePdSi3 weregrown by the Pb-flux method. The crystal structureof CePdSi3 was confirmed to be the BaNiSn3 -type
NCS tetragonal structure, in which Rashba typespin splitting is realized. Specific heat andmagnetization measurements revealed threesuccessive magnetic transitions at TI = 4.85(5) K, TII= 2.78(5) K, and TIII = 2.30(5) K under zero magnetic
field. Below TII, the development of a weakferromagnetic component was observed, as shownin the inset of Fig. 1. This ferromagnetic moment (mo~ 0.005 μB f.u.-1 at 1.85 K) is rather smaller than the
expected value from the Γ6 crystalline-electric-field
ground state of the Ce3+ ion, so that a canted antiferromagnetic ground state may be realized in CePdSi3.

Fig. 1 Magnetic field dependence of the normalized
magnetization of CePdSi3 where Ms = 1.23 μB f.u.-1 andχpara = 1.46x10 -6 μB f.u.-1.Oe-1 [2]. Weak ferromagnetismin CePdSi3 is evident from the hysteresis curves at 1.85 K
for H // [100] shown in the inset. The weak ferromagnetismand anisotropic metamagnetic behaviors clearly indicate
the existence of complex magnetic interactions in thissystem.

Interestingly, unusually complex metamagnetic
behaviors were observed below TIII, as shown in
Fig. 2, indicating the existence of complex magnetic
interactions in this system. Such multiple metamagnetism was not observed in centrosymmetriccompounds with a similar tetragonal structure (e.g.,
CePd2Si2 [3]). Thus, we can argue that the unusuallycomplex magnetism in CePdSi3 is associated with
the PSB effect inherent in the NCS CeTSi3 systems.
Further comprehensive studies are indispensablefor the understanding of the PSB effects on themagnetic and transport properties of the NCS heavy
fermion systems.
References[1] Non-centrosymmetric superconductors: Introduction andOverview, ed. E. Bauer and M. Sigrist (Springer, 2012) andreferences therein.
[2] D. Ueta, Y. Ikeda, and H. Yoshizawa, J. Phys. Soc. Jpn. 85,
104703 (2016).
[3] I. Sheikin, A. Gröger, S. Raymond, D. Jaccard, D. Aoki, H.
Harima, and J. Flouquet, Phys. Rev. B 67, 094420 (2003).

Keywords: parity symmetry breaking, magnetic, heavy fermion
Yoichi Ikeda (Metal Physics with Quantum Beam Spectroscopy Division)
E-mail: yo1iked@imr.tohoku.ac.jp
URL: http://qblab.imr.tohoku.ac.jp/

IMR KINKEN Research Highlights 201731

Electronic Materials

Atom Probe Analysis of Silicon Nanocrystals Embedded in
Silicon Dioxide Matrix

Silicon (Si) nanocrystals (NCs) in a Si dioxide (SiO ) matrix have attracted considerable attention due to their2potential applications in electronic devices. Single planes of Si NCs embedded in a SiO2 matrix were synthesizedby annealing SiO2/SiO/SiO2 multilayers. The dependence of the structural characteristics of the Si NCs on theinitial SiO layer thickness was investigated using atom probe tomography and validated by energy-filteredtransmission electron microscopy.

Silicon (Si) nanocrystals (NCs) embedded in a
Si dioxide (SiO2) matrix have been extensively
studied due to their potential applications such as inphotovoltaics and opto- and nano-electronics. Theirproperties rely on the structural characteristics of
the Si NCs: shape, size, and areal density. A
comprehensive investigation of the relationshipbetween the initial SiO layer thickness (tSiO) andstructural characteristics of the Si NCs is challenging
due to the intrinsic limitation of the conventional
analytical techniques.
Laser-assisted atom probe tomography (APT)enables us to obtain three-dimensional (3D) atom
maps of nanostructures [1]. Here, we report on the
APT study of the evolution of Si NCs structuralcharacteristics as a function of the thickness of theinitial SiO film [2].
A single plane of a Si NC layer was synthesizedby processing 4, 6, and 10 nm thick SiO layers at
high temperatures, as shown in Figure 1(a). Figures
1(b) and 1(c) show the plan-view energy-filteredtransmission electron microscope (EFTEM) image
and APT map of the sample with 6-nm-thick SiO
film, respectively. While the EFTEM image only
provided information about the projection of the Si
NCs, APT provided a greater insight into the 3D
structural characteristics.
In the cluster analysis based on the APT maps,
the Si NCs were fitted as ellipsoids using the best-fit
ellipsoid method from which the dimension of thesemi-axes (X1, X2, and X3 are the major semi-axes
and two minor semi-axes; X1 ≥ X2 ≥ X3) were
determined. Figure 1(d) shows the shape
distributions in terms of aspect ratio (X2/X1) andoblateness (X3/X2). It was found that the Si NCs in all
the three samples were mainly extended spheroids.
In addition, many rod-shaped Si NCs appeared forthe thickest SiO layer (10 nm), which were connectedby small Si NCs.
The proposed combination of TEM and APT
analyses provides an exhaustive picture of theFig. 1 (a) Schematic structure of Si NCs layer in SiO2 matrix.
(b) Plan-view EFTEM image and (c) corresponding 3D
atom map (tSiO=6 nm). (d) Shape distribution withdifferent initial thicknesses of the SiO layer.

system. Using a single layer of Si NCs, a directcomparison between TEM and APT is possible,
providing a self-consistent description of the Si NC
morphology. Our experimental results demonstratethat the Si NCs get progressively bigger withconcomitant evolution of the shape, from spheroids
to rod-shaped nanostructures, with an increasing in
the initial SiO layer thickness.
References[1] B. Han, Y. Shimizu, J. Wipakorn, K. Nishibe, Y. Tu, K. Inoue, N.
Fukata, and Y. Nagai, Nanoscale 8, 19811 (2016).
[2] B. Han, Y. Shimizu, G. Seguini, E. Arduca, C. Castro, G. Ben
Assayag, K. Inoue, Y. Nagai, S. Schamm-Chardon, and M.
Perego, RSC Adv. 6, 3617 (2016).

Keywords: atom probe tomography, nanostructure, electronic material
Yasuo Shimizu, Koji Inoue, and Yasuyoshi Nagai (Irradiation Effects in Nuclear and Their Related Materials Division)
E-mail: yshimizu@imr.tohoku.ac.jp
URL: http://wani.imr.tohoku.ac.jp/index.html

32

IMR KINKEN Research Highlights 2017

IMR KINKEN Research Highlights 2017

Cleaved ScAlMgO4 (0001) as a Suitable Substrate for GaN
Epitaxial Growth by Metalorganic Vapor Phase EpitaxyCleaved ScAlMgO4 (SCAM) substrates with small lattice mismatch of 1.8% to GaN were used for metalorganic
vapor phase epitaxial growth of GaN. A single crystalline GaN film with a flat surface and a small residual strain
was obtained. These results reveal that the cleaved SCAM substrate is very promising for nitride semiconductors.
In order to realize a sustainable society, further
improvement of nitride-based devices, including
light emitters and optical detectors, high-power andhigh-frequency transistors, and high-efficiency
tandem solar cells is indispensable. To date,sapphire substrates with a large lattice mismatch of
14% to GaN have been usually used. This context
shows that, ScAlMgO4 (SCAM) with a small latticemismatch of 1.8% to GaN is attractive. A two-inchsize boule of SCAM can be grown by the Czochralski
method. Moreover, SCAM can be cleaved along thec-plane as illustrated in Fig. 1(a). We have confirmed
the cleavage position by using the X-ray crystal
truncation rod scattering method. Thus, atomicallyflat c-plane substrates with large diameters can beeasily prepared just by cleavage without slicing by acutter and polishing. This leads to the drastic cost
reduction in substrate fabrication.
The successful growth of flat and high-quality
GaN films by metalorganic vapor phase epitaxy(MOVPE) indicates that the SCAM substrate is
resistant to the MOVPE environment [1]. The film
was proven to be (0001) Ga-polar due to thediscrimination of etching with a KOH aqueous
solution, as illustrated in Fig. 1(b). This result was
carefully verified by anomalous scattering X-ray
diffraction measurements using a continuousenergy X-ray. The residual strain of a 2-µm-thick film
was characterized by the reciprocal space mappingof X-ray diffraction as shown in Fig. 2. The c- anda-axis lattice constants of GaN were measured tobe 5.187 and 3.187 Å, respectively. From theseresults, the strains are 0.029% and -0.055% along
the c-axis and a-axis, respectively. These strains
are almost half of the strains in a Ga-polar GaN filmgrown on a sapphire substrate [2]. Hence, SCAM isa very promising substrate material for nitride
semiconductors grown using MOVPE.
SCAM is also expected to be a potential
substrate for bulk GaN fabrication via the halide
vapor phase epitaxy (HVPE) growth method owing
to its small residual strain, small bowing, and thefeasibility of substrate removal by cleavage.

Fig. 1 Cross-sectional atomic structure of (a) SCAM andcleavage planes, and (b) an interface model of Ga-polar
GaN grown on a cleaved SCAM substrate.

Fig. 2 Reciprocal space map around SCAM (01123) andGaN (0115). The void center of the white cross indicatesthe point for bulk GaN.

References[1] T. Iwabuchi, S. Kuboya, T. Tanikawa, T. Hanada, R. Katayama,
T. Fukuda, and T. Matsuoka, Phys. Status Solidi A, 1-8, DOI:
10.1002/pssa.201600754 (2016).
[2] K. Shojiki, T. Hanada, T. Tanikawa, Y. Imai, S. Kimura, R.
Nonoda, S. Kuboya, R. Katayama, and T. Matsuoka, Jpn. J.
Appl. Phys. 55, 05FA09 (2016).

Keywords: nitride, thin films, vapor phase epitaxy (VPE)
Takashi Matsuoka (Physics of Electronic Materials Division)
E-mail: matsuoka@imr.tohoku.ac.jp
URL: http://www.matsuoka-lab.imr.tohoku.ac.jp/?TOPPAGE_ENG

IMR KINKEN Research Highlights 201733

Electronic Materials

Distribution of Mn in Pink Elbaitic TourmalineT

he local distribution of Mn in a pink elbaitic tourmaline sample from Mogok, Myanmar, was studied using the
Mn K-edge X-ray absorption fine structure technique. The observed edge energy of Mn corresponds to that of
Mn2+, and the nearest neighbor Mn-O distance of 2.09 Å supported the overall preference of Mn2+. The present
study also describes detailed structural features determined from single crystal X-ray diffraction.
Elbaite, Na(Li1.5,Al1.5)Al6(Si6O18)(BO3)3(OH)4, is
one of the alkali-tourmaline subgroup minerals. A
variety of studies on elbaite and its relatives haveexamined the mechanism for its interestingcoloration with respect to minor elements. Figure 1
shows the structure of elbaite, with the octahedral
Y-site and Z-site, and it is suggested that the
distorted Y-site is a key for the incorporation of theinteresting minor elements. Nevertheless, ordinary
single crystal X-ray diffraction is insufficient todiscern the distribution of a minor constituent anddetermine its valence state; therefore, an alternative
experimental approach is strongly required. This
prompted us to analyze the distribution of Mn in pinkelbaite from Mogok, Myanmar, by using both single
crystal X-ray diffraction and X-ray absorption finestructure measurement.
The chemical formula for the elbaite was
Na 0.70 (Li 0.60Al2.40)Al 6 (BO3) 3 (Si5.59 B 0.41O18)(OH) 3O,
which agrees well with the empirical formula Na0.56
C a 0 . 0 4 ( L i 0 . 8 2 M n 2+ 0 . 2 2 M n 3 + 0 .1 5 F e 0 . 0 1 A l 1. 8 ) A l 6(BO3) 3 (Si5.71Al 0.19 B 0.10 O18)(OH) 3 (OH 0.39 F 0.12 O 0.49).
Single crystal X-ray diffraction results indicated an
occupation of 0.60 Li and 2.40 Al at the Y-site andthe scattering power for the Y-site is in reasonableagreement with that calculated from the empiricalformula. The obtained Y-O distances also suggest
the existence of an element with a large ionic size.
This readily supports the existence of Mn and Fe at
the Y site. On the other hand, the Z site was assumed
to be completely occupied by Al and the refineddisplacement parameter indicates no significant
occupation by other elements. Six Z-O distances
obtained are between 1.884 and 1.967 Å, and theaverage value of 1.908 Å agrees with those of Al
sites of common tourmaline samples.
Figure 2 shows the experimental extended
X-ray absorption fine structure (EXAFS) profile of theelbaite alongside the simulated EXAFS profile for amodel in which Mn resides at the Y site, suggestingthat the model in which Mn prefers the Y site agrees
well with the experimental data. Further least-square
fitting for the first neighbor Mn-O coordination

Fig. 1 The c-axis projection of elbaite structure.

Fig. 2 EXAFS simulation of Mn K-edge k3 -weighted χ(k)functions. Solid line: the simulated one obtained by the
Y-site model; dashed line: experimental data.

allowed us to obtain the averaged Mn-O distance of
2.09 Å, and this leads to the population of Mn2+/Mn =0.6. These results clearly indicate that the distributionof Mn3+ at the distorted Y site is responsible for thepink color of the present sample [1].
References[1] K.Sugiyama, H.Arima, H.Konno, and T. Kawamata, J . Min.
Petr. Sci. 111, 1 (2016).

Keywords: tourmaline, structure, XAFS
Kazumasa Sugiyama and Hiroshi Arima (Chemical Physics of Non-Crystalline Materials Division)
E-mail: kazumasa@imr.tohoku.ac.jp
URL: http://www.xraylab.imr.tohoku.ac.jp/

34

IMR KINKEN Research Highlights 2017

IMR KINKEN Research Highlights 2017

Electrical On-and-Off Switching of Magnetism in a Donor/
Acceptor Metal–Organic Framework Using a Li-Ion Battery

Reversible magnetic control between paramagnetic and ferrimagnetic phases has been demonstrated during

charge/discharge cycling in an electron-donor/acceptor metal–organic framework incorporated in a Li-ion
battery. Selective electron doping into the acceptor sites in the framework, accompanied by Li-ion migrationsin the pores, based on the battery voltage led to a “magneto-ionic” control for a bulk material, which motivates
us to create electrically switchable non-volatile magnets.

Electrical control of magnetism has attracted
much attention in the field of materials science andspintronics [1]. Various approaches for magnetism
control using electrical means such as magnetic
domain reversal by polarized spin-current flow andelectric-field modulation of magnetic anisotropy havebeen suggested so far. Electron-filling control using
field effect transistor (FET) in correlated electron
systems is also one of the effective approaches inmodulating magnetic properties. In diluted magnetic
semiconductors, the stability of the ferromagnetic
phase is successfully controlled by tuning theelectron density using FET. However, the applicationof FET for filling-control is limited to thin-films or
materials interfaces due to the electrostatic screening
effect by the electric-field-induced carriers.
On the other hand, the Li-ion battery (LIB)
system is another filling control device, which isapplicable for bulk materials. In an LIB system, Li+ion migration accompanied by a redox reaction in
the electrodes is used for energy storage. In thissituation, the electron density of the electrodematerial can be controlled because an equal
number of electrons and Li+ ions must be introducedto (or extracted from) the material. In our recent
studies, taking advantage of this LIB characteristic,
we have attempted reversible electrical magnetism
control in bulk compounds [2, 3].
As a candidate material, we have focused onelectron-donor/acceptor metal-organic frameworks(D/A-MOFs), which consist of paddlewheel-type
diruthenium (II, II) complexes as the donor (D) unit
and TCNQ derivatives as the acceptor (A) unit.
Since these D/A-MOFs are porous redox-active
compounds, they are suitable for LIB electrodes.
Notably, in these D/A-MOFs, magnetic ordering
occurs when A is in a radical state with a half spin.
Hence, we have carried out selective electron-filing
control of the A-sites in the D/A-MOFs throughbattery voltage tuning, and as a result, foundrepeatable phase switching between paramagnetic

Fig. 1 (a) Schematic figure of magnetism control in a D/AMOF by an LIB system.
(b) Reversible on-and-off magnetic phase switching byin situ LIB cell.

and ferrimagnetic states with the discharge/charge
cycle of the LIB.
The switched magnetic states were nonvolatile
without a continuous electric power supply. These
results could open up a new avenue of research in
the emerging field of magneto-ionics.
References[1] F. Matsukura, Y. Tokura, and H. Ohno, Nat. Nano. 10, 209(2015).
[2] K. Taniguchi, K. Narushima, J. Mahin, W. Kosaka, and H.
Miyasaka, Angew. Chem. Int. Ed. 55, 5238 (2016).
[3] K. Taniguchi, K. Narushima, H. Sagayama, W. Kosaka, N.
Shito, and H. Miyasaka, Adv. Func. Mater. 27, 1604990 (2017).

Keywords: magnetic properties, molecular devices, 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/cn5/HOME-Eng.html

IMR KINKEN Research Highlights 201735

Electronic Materials

Low Field Magnetization Switching Mediated by Vortex
Dynamics

M

agnetic vortex dynamics strongly affects the magnetic structures of environment. We fabricated nanodots
of an exchange-coupled bilayer with a soft magnetic Ni81Fe19 having a magnetic vortex and a perpendicularly
magnetized L10 -FePt exhibiting a large switching field. The azimuthal spin waves in the magnetic vortex of
Ni81Fe19 triggered the reversed-domain nucleation in L10 -FePt, which led to low field magnetization switching.

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

36

IMR KINKEN Research Highlights 2017

a

b

10
8

H sw (kOe)

A magnetic vortex in a soft magnetic disk is anin-plane curling magnetic structure having a core
whose magnetic moments are normal to the disk
plane. Magnetic vortices have fascinated us
because of their unique functionalities and rich
physics [1]. Several kinds of non-equilibrium
dynamical motion can be excited by applying an rf
magnetic field (Hrf) or injecting spin current, which
provide promising applications, e.g., a vortex-typemagnetic random access memory and a spin torquevortex oscillator. Although many studies related to amagnetic vortex focus on the control of magnetic
moments in the vortex [2], none has tried to use themagnetic vortex dynamics in a soft magnet as aroute to switching the magnetization of a hardmagnet. Here, we show that the Hrf-induced vortex
dynamics in soft magnetic Ni81Fe19 (permalloy; Py)
trigger the magnetization switching of hard magnetic
L10 -FePt at a low magnetic field (H) [3].
We exploited a nanodot array consisting of an
exchange-coupled bilayer with a hard magnetic
L10 -FePt layer and a soft magnetic Py layer, which isschematically illustrated in Fig. 1 (a). The thin films
were grown on an MgO (100) single crystal substratein the stacking order of MgO Subs. || Fe (1) | Au (60)
| L10 -FePt (10) | Py (150) | Au (5) | Pt (3) (in nanometers)by sputtering. The films were microfabricated into
circular nanodots with a diameter of 260 nm byelectron beam lithography and Ar ion milling. The
10-nm-thick
L10 -FePt
hadlarge
uniaxial
magnetocrystalline anisotropy (Ku) perpendicular tothe disk plane, leading to perpendicularmagnetization. On the other hand, micromagnetic
simulation suggested the formation of magnetic
vortex in the 150-nm-thick Py layer.
From the magnetization curve and theanisotropic magnetoresistance curve for the
nanodot array, we recorded a large Hsw of 8.6 kOe
for L10 -FePt without exciting the dynamics of themagnetic vortex. In order to examine the effect ofvortex dynamics on Hsw, we applied Hrf of 200 Oe to
the nanodots to excite the vortex dynamics in Py.
Figure 1 (b) shows a plot of Hsw as a function of

Py
FePt

6
4
2
0
0

Experiment
Simulation
5

10

15

20

25

f (GHz)Fig. 1 (a) Schematic illustration of nanodots consisting of
perpendicularly magnetized L10 -FePt, and Py having themagnetic vortex. (b) Switching field (Hsw) as a function of
frequency (f) of an rf magnetic field.

frequency (f) of Hrf. Compared to Hsw with no applied
Hrf, a strong reduction of Hsw is evident in the rangeof 11 GHz ≤ f ≤ 17 GHz. In this f range, Hsw gradually
increases, and the values of Hsw in f ≥ 18 GHz are
almost the same as those in 6 GHz ≤ f ≤ 10 GHz.
Micromagnetic simulation and the detailed analysisof the magnetization reversal process revealed thatthe azimuthal spin waves having node in the radial
direction in Py played an important role for thereversed-domain
nucleationin
L10 -FePt.
Consequently, we achieved a reduction in Hsw for
L10 -FePt. This is regarded as a nonlocal
phenomenon in a coupled system.
Our results not only provide an insight into the
nucleation phenomena but also offer a new way for
information writing of magnetic storage, andspintronic applications.
References[1] S.-B. Choe, Y. Acremann, A. Scholl, A. Bauer, A. Doran, J.
Stöhr, and H. A. Padmore, Science 304, 420 (2004).
[2] B. Van Waeyenberge, A. Puzic, H. Stoll, K. W. Chou, T.
Tyliszczak, R. Hertel, M. Fähnle, H. Brückl, K. Rott, G. Reiss, I.
Neudecker, D. Weiss, C. H. Back, and G. Schütz, Nature 444,
461 (2006).
[3] W. Zhou, T. Seki, H. Arai, H. Imamura, and K. Takanashi, Phys.
Rev. B 94, 220401(R) (2016).

IMR KINKEN Research Highlights 2017

Challenge to Produce Amorphous-Si from Supercooled
LiquidAmorphous silicon (a-Si) is mainly used in solid-state electronics and photovoltaic technologies, and is usually

produced as thin films by chemical vapor deposition. The preparation of bulk a-Si from liquid (l-) Si has long
been a challenge since all attempts have failed so far. The purpose of this study is, therefore, to produce bulk
a-Si directly from l-Si.

Atomic and electronic properties of l-Si arelargely different from those of a-Si: l-Si is metallic
and its coordination number is about 6, whereas
a-Si is semiconducting and its coordination number
is 4. The transformation from l-Si to a-Si could be afirst-order phase transition, which releases latentheat. Therefore, obtaining “bulk” a-Si directly fromthe melt is extremely challenging. Recently, Turnbull
et al. have proposed that a-Si can be obtained fromsupercooled states below 1440 K [1].
However, it is difficult to cool liquids to several
hundred K below the melting temperature (Tm: 1683
K) because liquids are generally held in containers
or crucibles. When the temperatures of liquids
decrease below Tm, heterogeneous nucleation at
the wall of the container occurs and crystallization
starts; thus, the temperature of liquid does notdecrease below Tm.
We have developed a unique liquid-quenchingsystem including an electrostatic levitator (ESL). In
the ESL system, a sample is levitated between two
horizontal electrodes using electrostatic forces via a
feedback loop (Fig. 1). The sample is heated andmelted using the focused beams of three 100
semiconductor lasers at a wavelength of 980 nm.
The radiance temperature is measured by pyrometryat the wavelength of 2.4 µm. A feature of our system
is to hold the sample via Coulomb forces instead ofusing a crucible (i.e., the sample is free from thecontainer walls) throughout the processing. Thisway, we can achieve and maintain the supercooled
states of l-Si.
Our experimental procedure was as follows.
The high-purity polycrystalline Si sample was melted
and kept in the molten state at 1883 K for several
seconds. Then, turning off the heating laser beams,
the l-Si droplet was cooled by radiation from thesurface. When the temperature of the droplet
decreased to that of supercooled states, the highvoltage used for levitating the droplet was switched
off, and it fell through a hole in the bottom electrode.
The falling droplet came in contact with a metal
plate and quenched. The thickness of the quenchedsample was 10–200 µm.
Though the X-ray diffraction pattern pattern ofthe quenched sample showed only the diffraction

Fig. 1 Interior of the ESL chamber: A spherical sample islevitated between two horizontal electrodes using
electrostatic forces. The bottom electrode is electricallygrounded. An electrical field of about 10 kV is applied tothe top electrode to levitate the sample against gravity.

Fig. 2 An scanning electron microscope image of thequenched sample from supercooled l-Si.

peaks of crystalline Si, a characteristic microstructure
was observed locally in the quenched sample (Fig.
2). The microstructure was composed of Si grains
with a diameter of several tens of nm. The
microstructure indicates that a-Si can locally form
once during the quenching process and thentransforms to crystalline Si grains by the latent heatfrom the surroundings. We hope to obtain bulk a-Si
by further improving the quenching method.
References[1] Y. Shao, F. Spaepen, and D. Turnbull, Metall. Mat. Trans A 29,
1825 (1998).

Keywords: amorphous, Si, supercooled liquid
Junpei Okada and Satoshi Uda (Crystal Chemistry Division)
E-mail: junpei.t.okada@imr.tohoku.ac.jp
URL: http://www.uda-lab.imr.tohoku.ac.jp/ index.html

IMR KINKEN Research Highlights 201737

Electronic Materials

Development of Eutectic Scintillators for High-Resolution
Radiation Imaging

The development of submicron-diameter phase-separated scintillator fibers such as GdAlO (GAP)/α-Al O ,3

2

3

SrHfO3/Al2O3, Gd2Si2O7/SiO2, and LiF/ CaF2/LiBaF3 was reported for high-resolution X-ray imaging. In addition,
we developed a large area eutectic growth technique by the micro-pulling-down method, and eutectic GAP/αAl2O3 with 25x25 mm2 area was fabricated by this method. Furthermore, X-ray Talbot imaging was demonstratedusing the GAP/α-Al2O3 PSSFs.
Scintillators coupled with photodetectors arewidely used in radiation imaging applications such as
medical imaging, security, high-energy physics,
astrophysics, and oil well logging. In the X-ray
imaging applications, radiation imaging sensors arecomposed of photodetector arrays and indirect flat
panel detector (FPD) coupled with a scintillator plate.
Here, we propose submicron-diameter phaseseparated scintillator fibers (PSSFs) exhibiting boththe properties of an optical fiber and X-ray-to-light
conversion. The PSSFs were fabricated using a
directionally solidified eutectic (DSE) system. In
PSSFs, the light emitted from the scintillator fibers is
confined and transported along the fiber direction
by a total reflection mode, as shown in Fig. 1(a), sothat high-resolution X-ray imaging can be achieved.
So far, we have reported on PSSFs such as
GdAlO3(GAP)/α-Al2O3 [1],SrHfO3/Al2O3 [2],Gd2Si2O7/SiO2 [3], LiF/CaF2/LiBaF3 [4], and LiF/
LiGdF4 [5].
In addition, we developed a large area eutectic
growth technique by the micro-pulling-down
method. An Ir crucible was designed with a 25x25mm2 die (Fig. 2 (a)). By using this crucible, eutectic
GAP/α-Al2O3 with 25x25 mm2 area was fabricated(Fig. 2 (b)).
Furthermore, X-ray Talbot imaging wasdemonstrated by using GAP/α-Al2O3 PSSFs. The
GAP/α-Al2O3 PSSFs with 0.3 mm thickness were
coupled with a fiber optic plate and mounted on a
CMOS sensor (Fig. 3 (a)). Finally, X-ray Talbot
images of a nylon ball with 4 mm diameter wereobtained using the imaging apparatus (Fig. 3).

Fig. 1 (a) Schematic of the GAP/α-Al2O3 PSSFs. (b)Diagonal view of the cut and polished sample.

a)b)

Fig. 2 (a) Photograph of the Ir crucible with 25x25 mm2 die.
(b) Diagonal view of the cut and polished 25x25 mm2
sample.

References[1] T. Den, et al IEEE Trans. Nucl. Sci. 60, 16 (2013).
[2] K. Kamada,et al, J. of Phys. Conference Series 619, 012036(2015).
[3] K. Kamada,et al, Opt. Mater 41, 41 (2015).
[4] K. Hishinumaet al, Jpn. J. Appl. Phys. 54, 04DH04 (2015).
[5] K. Kamada,et al, Opt. Mat. 92, 134 (2016).

Keywords: eutectics, scintillator, X-ray imaging
Akira Yoshikawa (Advanced Crystal Engineering Laboratory)
E-mail: yoshikawa@imr.tohoku.ac.jp
URL: http://yoshikawa-lab.imr.tohoku.ac.jp/index-e.html

38

IMR KINKEN Research Highlights 2017

Fig. 3 (a) Photograph of the imaging apparatus using the
PSSFs coupled with a fiber optic plate on the CMOS
sensor. (b) X-ray Talbot imaging of a nylon ball.

IMR KINKEN Research Highlights 2017

Pressure-Induced Valence Transition and Novel Electronic
Behavior in Rare-Earth Compound EuRh2Si2T

Temperature (K)Electrical resistivity (µΩ.cm)

he rich variety of f-electron compounds provides ample opportunities for a systematic study of theircharacteristic physical properties. EuRh2Si2 shows valence transition at a pressure of about 1 GPa from the
Eu-divalent (antiferromagnetic) state to a nearly trivalent (non-magnetic) state. Tuning of the valence state underapplied pressure is reflected by a dramatic change in the temperature dependence of the electrical resistivity
in a EuRh2Si2 single crystal.
150
Eu atoms in a compound exhibit two kinds ofEuRh2Si2
Tmax
valence states, i.e., Eu2+ (4f 7 6s 2) and Eu3+ (4f 6 5d1
J || [100]23.26s ). Most of the Eu compounds are in the divalent
2.1
3.9
100
Tv
electronic state and order magnetically, while some
4.5 5.0
Eu compounds are in the trivalent electronic state.
1.3
Tv
Eu valence can be tuned by temperature, magnetic
1.0
50 TN
field, and pressure. In particular, pressure-induced
valence transition has attracted much attention for
P = 0 GPa
their unique electronic states. EuT2X2 (T: transition
metal, X: Si, Ge) is one of the most studied systems
0
0
100
200
300
exhibiting valence transition at ambient and/or highTemperature (K)pressures.
Fig. 1 T-dependence of the electrical resistivity of EuRh2Si2
EuRh2Si2 shows valence transition at a pressure
under high pressures.
of about 1 GPa from a Eu-divalent (antiferromagnetic)state to a nearly Eu-trivalent (paramagnetic) state,
300
which has been previously clarified using
polycrystalline samples. We have successfully
EuRh2Si2
grown single crystals of EuRh2Si2 and carried out
Tmax
detailed electrical resistivity measurements under
200
2+δ
Eu
pressure in order to elucidate the development of its
electronic state.
CEP
Figure 1 shows the temperature dependencesTV
100of the electrical resistivity ρ(T) under high pressuresof up to 5.0 GPa. At 0 GPa, ρ decreases steeplyTN
below the Néel temperature TN of 23.8 K. EuRh2Si2
Eu3-δ’
AF
indicates a clear first–order valence transition
0012
between 1 and 2 GPa, characterized by a large andPressure (GPa)prominent hysteresis in the ρ(T) curve. In theFig. 2 Pressure – temperature phase diagram of EuRh2Si2.
pressure region from 2 to 3 GPa, the first–ordervalence transition changed into the valence crossover like, and the ρ(T) curves exhibited a
the pressure evolution of the electronic states fromcharacteristic behavior in a moderate heavy-fermion
the nearly divalent (Eu2+δ) antiferromagnetically (AF)compound such as EuIr2Si2. Upon further increasingordered state to a moderate heavy-fermion stateand nearly trivalent state (Eu3- δ’), via the first-orderthe pressure, the ρ(T) curves revealed a normal
metallic behavior in a nearly trivalent (non-magnetic)
valence transition in Eu compounds.
electronic state such as EuCo2Si2.
From these results, a pressure – temperature
References
phase diagram of EuRh2Si2 was constructed, as[1] F. Honda, K. Okauchi, A. Nakamura, D. X. Li, D. Aoki, H.
shown in Fig. 2. We estimated the critical end point
Akamine, Y. Ashitomi, M. Hedo, T. Nakama, and Y. Onuki, J.
(CEP) of the valence transition as PCEP ~ 2 GPa andPhys. Soc. Jpn. 85, 063701 (2016).
TCEP ~ 170 K. This is the first detailed report unveiling
Keywords: electrical properties, valence transition, high pressure
Fuminori Honda (Actinide Materials Science Division)
E-mail: honda@imr.tohoku.ac.jp
URL: http://actinide.imr.tohoku.ac.jp/

IMR KINKEN Research Highlights 201739

Research Centers

IMR KINKEN Research Highlights 2017

ResearchResearch Centers

Titanium-Rich Precipitate Evolution in Vanadium-based
Alloys Studied by TEM and Positron Annihilation
Spectroscopy
International Research Center for Nuclear Materials Science

Microscopic evolution of plate-like Ti-rich precipitates in V-4Ti alloy during isochronal annealing was studied

by TEM and positron annihilation spectroscopy. Annealing out of mono-vacancy in the precipitates in the earlystage of evolution was successfully revealed.

IMR-Oarai has been the leading center inJapan for researches of nuclear materials andactinides, and is open to researchers all over theworld for collaborative studies. Herein, we introduce
collaboration with an overseas institute: a joint-study
on fusion-material with The University of Manchester,UK.
Vanadium-based alloys such as V-4Ti arepromising materials for the first wall in fusion reactors
due to low activation characteristics, goodmechanical properties, and high resistance to void
swelling. The swelling resistance is yielded mainlyby the Ti-rich precipitates; thus, their evolution athigh neutron doses and high temperatures isimportant for material development. We employed
TEM and positron annihilation spectroscopy toinvestigate the evolution of Ti-rich precipitates athigh temperatures.
Figure 1 (a) shows the SEM image for the asreceived V-4Ti alloy. Plate-like precipitates wereformed in high number density. The precipitates wereanalyzed by TEM. Figure 1 (b) shows the TEM
HAADF image of the superstructure and uniform
regions of the plate-like precipitates, while Figure 1(c) shows the composite image constructed from the
EELS maps. Thin layers of V/TiO are observed. The
alloy was isochronally annealed at 500 – 700 °C, and,TEM and positron annihilation measurements were
performed. TEM revealed almost no change in the
Ti-rich precipitates even after 700 °C annealing.
Figure 1 (d) shows the S and W parameters of
the coincidence Doppler broadening of positronannihilation radiation, which provide information on
the positron trapping sites. In the as-received state,
the S parameter was higher than that of pure V,
suggesting positron trapping at vacancies inside
the Ti-rich precipitates. During isochronal annealing,
the correlation points moved toward pure V withincreasing temperature. This implies the recovery ofvacancies inside the Ti-rich precipitates, despite noFig. 1 (a) SEM image of the V-4Ti alloy (as-received). (b)and (c) TEM HAADF image and EELS map of thesuperstructure and uniform regions of the plate-like TiO
precipitate in the V-4Ti alloy (as-received). (d)Correlation between the S and W parameters ofcoincidence Doppler broadening measurement of
positron annihilation for the V-4Ti alloy annealed at
different temperatures, together with data for reference
V. The directions of references Ti and SiO2 (substitutematerial for TiO2) are also shown.

change in the TEM observations.
References[1] A. Impagnatiello, T. Toyama, and E. Jimenez-Melero, J. Nucl.
Mater. 485, 122 (2017).

Takeshi Toyama (Corresponding Author, International Research Center for Nuclear Materials Science)
E-mail: ttoyama@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 2017

IMR KINKEN Research Highlights 2017

Determination of Superconducting Gap Structure in the
Heavy-Fermion Antiferromagnet UPd2Al3
International Research Center for Nuclear Materials ScienceT

he understanding of superconducting (SC) nature in heavy-fermion compounds is one of the recent hot
topics of the strongly correlated electron systems. We have recently studied the SC gap symmetry in the heavyfermion antiferromagnet UPd2 Al3 by means of angle-resolved heat–capacity measurements at low temperatures
down to 0.1 K using a high-quality single crystal. Our results demonstrate that the field-orientation dependenceof heat capacity has a sufficiently high sensitivity to detect a horizontal line nodal gap structure in heavy bands.
In actinide based heavy-fermion compounds,
the 5f electrons acquire huge effective masses 1001000 times larger than that of ordinary conduction
electrons, and thus move very slowly in a crystal
lattice. In this situation, it is widely considered that
Cooper pairs of heavy electrons favor nodal gap
symmetry to avoid strong Coulomb repulsions,instead of isotropic s-wave superconductivity. The
determination of SC gap structure is of primary
importance for the exploration of non-phononic
pairing mechanisms, since the angular dependenceof the gap function is directly related to the pairing
interaction. However, the determination of SC gap
symmetry in uranium systems is by no means aneasy task; there have been numerous experimental
and theoretical works for over thirty years. For
example, the true nature of the SC gap in the oldest
uranium heavy-fermion superconductor, UBe13, hasbeen unraveled very recently [1].
In the present study [2], we have examined the
SC gap symmetry of the hexagonal heavy-fermion
in
which
the
antiferromagnet
UPd2 Al3,
antiferromagnetic order coexists with the SC state.
We
havemeasuredthefield-orientation
dependences of the heat capacity (C) in order toelucidate the SC gap structure from the viewpoint of
the heavy-electron density of states. Figure 1 shows
the anisotropic C(H)∝H1/2 behaviors and the twofold oscillation in the polar angle (θ) dependence of
C/T below 1 T in the SC state (T = 0.20 K). Moreover,
we found the evolution of a novel anomaly in C(θ)
around 45° at intermediate magnetic fields (1 < µ0H< 2 T) [Fig. 1(b)]. These experimental data provide
strong thermodynamic evidence for a horizontal line
node in heavy-electron bands (Fig. 2). The results
obtained by our high-precision experiments using ahigh-quality single crystal can provide crucial
indications for revealing the unconventional pairing
mechanisms in uranium heavy-fermion systems.

Fig. 1 (a) The magnetic field (H) and (b) polar-angle (θ)
dependences of heat capacity (C/T) in UPd2Al3 measured
at 0.20 K in the hexagonal ac plane (µ0Hc2 ~ 3.2 T) [2]. The
inset shows H1/2 dependence of C/T in low fields.

Fig. 2 The SC gap structure in UPd2 Al3 with a horizontal
line node on the Fermi surface.

References[1] Y. Shimizu, S. Kittaka, T. Sakakibara, Y. Haga, E. Yamamoto,H. Amitsuka, Y. Tsutsumi, and K. Machida, Phys. Rev. Lett. 114,
147002 (2015).
[2] Y. Shimizu, S. Kittaka, T. Sakakibara, Y. Tsutsumi, T. Nomoto,H. Ikeda, K. Machida, Y. Homma, and D. Aoki, Phys. Rev. Lett.
117, 037001 (2016).

Yusei Shimizu (Corresponding Author, International Research Center for Nuclear Materials Science)
E-mail: yuseishimizu@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/

IMR KINKEN Research Highlights 201743

Research Centers

Magnetic Properties and Fabrications of Single Crystals of
Heusler Alloys with Half-Metallic Electronic State
Cooperative Research and Development Center for Advanced MaterialsT

he center continues to investigate and develop new materials and their fabrication processes and explores
the possibility of their application as multi-functional materials for high technology such as energy saving,environmental and ecology, structural application, electronics and information, and biomedical applications.
Here, we highlight our recent research activity of investigating the fundamental physical properties of the halfmetallic Heusler alloys for application in the field of spintronics.
Much attention has been paid to some Cobased and Mn-based Heusler alloys in the field of
spintronics because their characteristic electronic
structures would be efficient as ferromagnetic
electrodes in the spin dependent devices [1-3]. We
fabricated single crystals of Co2MnSi and Mn2VAl
Heusler alloys in which the electronic structure has
been predicted to be half-metallic by theoreticalstudies. In order to investigate in detail the magnetic
properties and electronic state, resonant inelastic
X-ray scattering (RIXS) was measured using soft
X-rays in a magnetic field.
Figure 1 shows a single crystal of Mn2VAl alloy
made by the Bridgeman method at the crystal
making research station in our center, and the Lauepattern in (100) plane. The RIXS experiments were
performed using the high-resolution soft X-ray
emission station HORNET in BL07LSU in SPring-8.
The RIXS spectra were measured with right/left
circular polarizations at room temperature for Mn
and V L-edge.
Figure 2 (a) shows the RIXS spectra and RIXSMCD of Mn observed at the incident photon energyof 638.6 eV, while Figure 2 (b) shows the partial
density of states (PDOS) of Mn for L21-type ordered
Mn2VAl, together with the RIXS-MCD of Mn.
Magnetic circular dichroism (MCD) can be clearlyseen in Fig. 2 (a). The incident photon energy issuch that the X-ray absorption of the Mn L3 -edge
just starts to occur, so that the electrons in the innershell are excited to unoccupied electron states justabove the Fermi energy. The RIXS-MCD reflects thecurvature of PDOS in the minority spin state because
the density of states between the majority and theminority spin states are significantly polarized. Thisevidences the absence of the electrons in the
majority spin state around the Fermi energy, that is,
the half-metallic electronic state in the Mn2VAl
Heusler alloy.

Fig. 1 Single crystal of Mn2VAl and its Laue pattern in (100)plane.

Fig. 2 (a) RIXS spectra and RIXS-MCD of Mn measured at
the incident photon energy of 638.6 eV. (b) PDOS of Mn
for L21-type ordered Mn2VAl Heusler alloy, together
with the RIXS-MCD of Mn.

References[1] R. Ooka, I. Shigeta, Y. Sukino, Y. Fujimoto, R.Y. Umetsu, Y.
Miura, A. Nomura, K. Yubuta, T. Yamauchi, T. Kanomata, and
M. Hiroi, IEEE Mag. Lett. 8, 3101604 (2017).
[2] K. Minakuchi, R.Y. Umetsu, K. Kobayashi, K. Ishida, and R.
Kainuma, J. Alloys Compds. 645, 577 (2015).
[3] R.Y. Umetsu and T. Kanomata, Physics Procedia 75, 890(2015).

Rie Y. Umetsu (Corresponding Author, Cooperative Research and Development Center for Advanced Materials)
E-mail: rieume@imr.tohoku.ac.jp
Tadashi Furuhara (Head of Cooperative Research and Development Center for Advanced Materials)
E-mail: furuhara@imr.tohoku.ac.jp
URL: http://www.crdam.imr.tohoku.ac.jp/en/index.html

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IMR KINKEN Research Highlights 2017

Ferroelectricity by Magnon Bose-Einstein Condensation ina Quantum Spin Dimer System
High Field Laboratory for Superconducting Materials

We have recently found spin-driven ferroelectricity due to the magnetic-field-induced Bose-Einsteincondensation of magnon quasiparticles in the spin dimer system TlCuCl3. Superposition of the wave functions
inherent in a quantum magnet in its ground state plays a key role in the appearance of the ferroelectricity. The
ferroelectricity turned out to be very soft with an electric coercive filed E ~ 0.04 MV/m.
Magnetoelectric multiferroic materials with thecoexistence of magnetic order and ferroelectricity
have attracted much attention because the strong
coupling between magnetism and electric
polarization in such materials brings about enhanced magnetoelectric effects, which offer efficient
control of electric polarization by magnetic fields
and magnetization by electric fields. After the
discovery of spin-driven ferroelectricity in aperovskite-type manganese oxide, many materials,
which undergo spiral magnetic ordering, were foundto show multiferroic behaviors. The spiral order
lowers the symmetry of the system to be polar, thus
producingferroelectricity.
Thespin-driven
ferroelectricity in the spin dimer system TlCuCl3 is,however, not due to spiral ordering. TlCuCl3 is
known to show antiferromagnetic ordering by thefield-induced Bose-Einstein condensation (BEC) of
magnon, which is a triplet excitation on a dimer
propagating through the crystal lattice. In this BEC
phase, coherent superposition of the spin singlet
and triplet states occurs. It is important to note that
this superposed state has a finite expectation valueof the vector spin chirality Si × Sj, which is a key
quantity for the appearance of the spin-driven
ferroelectricity. From the high field pyroelectric
current measurement, we found that the developmentof Si × Sj in the BEC phase induces ferroelectricity.
Figure 1(a) shows the magnetic field dependence ofthe electric polarization in TlCuCl3. Above the criticalfield of 5.5 T, a finite spontaneous electric
polarization, which is proportional to the theoreticallycalculated Si × Sj, appears in the BEC phase. As
shown by the P-E hysteresis loop in Fig. 1(b), theobserved ferroelectricity is very soft. Its electric
coercive field E ~ 0.04 MV/m is, to the best of ourknowledge, the lowest among the spin-driven
ferroelectrics. Because the reversal of the electric
polarization requires 180° rotation of theantiferromagnetic domain around the external
magnetic field, this low coercive field arises from theFig. 1 (a) Magnetic field dependence of the electric
polarization in TlCuCl3 and (b) P-E hysteresis loop

isotropic nature of the BEC phase in TlCuCl3.
References[1] S. Kimura, K. Kakihata, Y. Sawada, K. Watanabe, M.
Matsumoto, M. Hagiwara, and H. Tanaka, Nat. Commun. 7,12822 (2016).

Shojiro Kimura (Corresponding Author, High Field Laboratory for Superconducting Materials)
E-mail: shkimura@imr.tohoku.ac.jp
Hiroyuki Nojiri (Head of High Field Laboratory for Superconducting Materials)
E-mail: hflsm@imr.tohoku.ac.jp URL: http://www.hflsm.imr.tohoku.ac.jp/cgi-bin/index.cgi

IMR KINKEN Research Highlights 201745

Research Centers

Scientific Breakthrough towards the 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 the enterprises in the Kansai areasponsored by the government, taking over the Kansai Center projects.
Trans-Reginal
Corporation
Centerwas
established in Osaka as a special unit in the Institutefor Materials 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, and Technology) and took over theKansai Center, which carried out its mission from2012 to 2016. The Trans-Reginal Corporation Centerhas three missions. First, to solve the technicalproblems that the industries have struggled toresolve. Second, the Center introduces academic
output to industries with the aim of applying suchoutput to society. Third, the Center helps educate
the next-generation materials scientists andresearchers in universities and enterprises. We haveorganized a bimonthly forum named “Monodukuri
Kisokoza”, which focuses on special topics
regarding materials and processing. Projects are
conducted through wide collaborations between
the government, universities, research institutions,and other organizations. The Center has four venues
to cover the Kansai area: the Osaka office at the
Osaka Prefecture University, the Hyogo office at the
University of Hyogo, the Sendai office in IMR, andthe Monozukuri Business Information Center Osaka(MOBIO) in the Creation Core Higashi-Osaka, agovernmental body where fourteen local universities
and two colleges are located to facilitate collaboration
with various industries.
The Center has developed various materials
and processes under collaboration with industries,
universities, and government organizations. One ofthem is to fabricate novel copper-based alloy wires,
which have been developed by IMR and TOKUSEN
KOGYO CO., LTD. The wires with Ti content ofapproximately 3.0 to 5.0 at% are fabricated by an
original and unique heat-treatment and then colddrawn; the former process promotes the precipitationof Ti-rich intermetallic precipitates and eventually
reduces the Ti content in the parent copper phase.
During the latter process, nanofibers of the Ti-richintermetallic precipitates disperse finely and densely

Fig. 1 Tensile strength and electrical conductivity of anovel copper-titanium alloy wire, together with that of
the representative copper-based alloy wires. “% IACS”
is defined as the percentile based on the electricalconductivity of an international annealed copper
standard (IACS) at 25 °C.

in the wire. As a result, the wire possesses an
excellent combination of strength and electricalconductivity, as shown in Fig. 1 [1]. The wires havegained considerable attention for applications inelectrical devices such as pins for micro-connectersand relay controls because of their superior
properties, which are competitive with those of theconventional Cu-Be alloys.
Similar collaborative researches for practicalapplications utilizing academic knowledge andindustrial technology are in progress. The TransRegional Corporation Center will make an effort toinnovate in the metallic material industry through thealliance with partners in the Kansai area andpromote scientific research in materials science.
References[1] S. Semboshi, S. Amano, J. Fu, A. Iwase, and T. Takasugi,
Metall. Mater. Trans. A 48, 1501 (2017).

Satoshi Semboshi (Corresponding Author, Trans-Regional Corporation Center for Industrial Materials Research)
E-mail: semboshi@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 2017

Magnetism Investigated by Supercomputer
Center for Computational Materials Science

Recent progress in magnetism-related studies by using supercomputers are presented. Of the two studies,

one was conducted by Professor Chen who explains the origin of the stability of NdFe12-based compounds,
and the other one is a new approach for evaluating finite temperature magnetism and was proposed by Mr.
Yamada.
Stability study of NdFe12-based compounds aspromisinghighperformancepermanent
magnetic materials a)
A series of the NdFe12-based (ThMn12-type)compounds have been predicted theoretically as
promising high performance permanent magnetic
materials
withhighmagnetization
andmagnetocrystalline anisotropy energy, which arecomparable to that of the well-known Nd-Fe-B [1].
However, it is very difficult to synthesize thesecompounds due to thermodynamical instability. The
electronic structures and the phonon vibration
spectra are calculated for these systems from thefirst-principles to investigate the origin of the instability
in these compounds. The results revealed that: (1)
NdFe12 has both thermodynamic and dynamic
instabilities, but tends to be dynamically stable whencompressed to a volume of -6%(Fig. 1); (2) the lattice
vibration effect at finite temperature stabilizes NdFe12
at 620 K; and (3) Ti substitution of an Fe atom
improves the stability of NdFe12, which can be
attributed to the effect of attractive pair interactions
introduced into NdFe11Ti due to Ti-doping.
Cluster Variation Calculation of Magnetictransition temperature b)
Cluster Variation Method has been recognized
as a reliable theoretical tool to incorporate wide
range of atomic correlations into the free energy
formula. Recently, further development has beenachieved in the Continuous Displacement Cluster
Variation Method (CDCVM), which is able toincorporate local lattice relaxation often realized
when mixing atoms of different sizes. The basic
purpose of the CDCVM is to convert the additional
freedom of local lattice relaxation into configurational
freedom of a multicomponent alloy. It is realized thatsuch a conversion of the internal freedom of an alloy
can be applied to magnetic moments, which changeboth magnitude and direction with temperature. We
focused on the calculation of Curie temperature of

Fig. 1 Phonon density of states at various volumes in NdFe12(v0 is the equilibrium volume).

Fig. 2 Each circle in different color indicates atomic species
representing different magnitude of magnetic moment.

pure Ni, for which seven magnetic moments wereintroduced, as shown in Fig. 2, and they wereregarded as seven atomic species displayed incolors. The interaction energies between themagnetic moments were obtained by first-principles
electronic structure calculations and the entropy
was evaluated via tetrahedron approximation of theCVM. From the temperature dependence of thelong-range order parameter, the Curie temperature
was estimated as 425 K, which is lower than theexperimental result by about 200 K. The revised
calculations are underway, and are being performed
by introducing more than seven magnitudes ofmagnetic moment.
References[1] Y. Harashima, K. Terakura, H. Kino, S. Ishibashi, and T. Miyake,Phys. Rev. B 92, 184426 (2015).

a) Ying Chen (Corresponding Author, Department of Finemechanics, School of Engineering)E-mail: ying@rift.mech.tohoku.ac.jpb) Ryo Yamada (Virginia Polytechnic Institute and State University) and Tetsuo Mohri (Corresponding Author, IMR)
E-mail: tmohri@imr.tohoku.ac.jp
http://www-lab.imr.tohoku.ac.jp/~ccms/Eng/index.php

IMR KINKEN Research Highlights 201747

Research Centers

High-Efficiency Energy Conversion Materials Based on
Correlation Between Heat, Spin, and Electric Field
Collaborative Research Center on Energy MaterialsT

he development of high-efficiency energy conversion materials based on the correlation between heat, spin,and electric field is an interesting and challenging topic. We aim to apply the Nernst effect in magnetic materials
to achieve a high-efficiency energy conversion method. Here, we highlight recent advances in fundamental
research and the application of the effect; the enhancement of anomalous Nernst effect by the spin-wave
generated by a temperature gradient and the control of anomalous Nernst effect by an external electric field.
One of our Center’s research activities is
directed toward the development of high-efficiency
energy conversion materials based on the correlation
between heat, spin, and electric field. This researchaims to replace existing energy materials andestablish the scientific principle on the technology
of energy conversion and the solution for the wideranging energy problems. We aim to apply the
Nernst effect in magnetic materials for a highefficiency energy conversion method. When atemperature gradient is applied to a material withspontaneous magnetization, an electric field is
induced in the direction perpendicular to both thetemperature gradient and the magnetization. Thisphenomenon is termed the anomalous Nernst effect(ANE). Obtaining materials with a large ANE isindispensable to enable its practical application. We
have previously reported the dependence of ANE
on material type in several perpendicularly
magnetized ordered-alloy thin films [1]. In thishighlight, the enhancement of ANE in a particularordered-alloy material “L10 -ordered FePt” wasinvestigated both experimentally and theoretically.
In addition, the control of ANE by an external electricfield was demonstrated in manganite thin films.
L10 -ordered FePt is known to exhibit a large
magnetic anisotropy. The electronic structure of thismaterial was measured by hard X-ray photoemission
spectroscopy to investigate the relationship between
the electronic structure and magnetic anisotropy [2].
Subsequently, the temperature dependence of ANE
in L10 -ordered FePt thin films with different magnetic
anisotropies was systematically measured. It was
found that the enhancement of ANE over 100 K
occurred particularly for FePt with small magnetic
anisotropies. It is considered that the spin-wave
generated by the temperature difference led to theenhancement of ANE in FePt. The theoretical
calculation of the spin–wave successfully depicted
the observed enhancement. The effect of theelectric field on thermomagnetic properties in a
La0.7Ca0.3MnO3 thin film was investigated using a

Fig. 1 (Top) Schematic of ANE measurement. (Bottom)
Nernst voltage (VN) as a function of magnetic field withdifferent applied gate voltages measured at 130 K with anin-plane temperature difference of 5 K.

FET structure with an Al2O3 dielectric-gate as show
in Fig. 1. The anomalous component of the Nernst
voltage clearly changed with the gate voltage. Thisimplies that the Nernst effect can be modulated by
the electric field, which is advantageous for thecontrol of thermomagnetic properties in various
magnetic materials with a high efficiency.
References[1] K. Hasegawa, M. Mizuguchi, Y. Sakuraba, T. Kamada, T.
Kojima, T. Kubota, S. Mizukami, T. Miyazaki, and K. Takanashi,Appl. Phys. Lett. 106, 252405 (2015).
[2] S. Ueda, M. Mizuguchi, Y. Miura, J. G. Kang, M. Shirai, and K.
Takanashi, Appl. Phys. Lett. 109, 042404 (2016).

Masaki Mizuguchi (Corresponding Author, Collaborative Research Center on Energy Materials)
E-mail: mizuguchi@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/index.html

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IMR KINKEN Research Highlights 2017

Investigation of the Electronic Structure and Spectroscopyof Organometallic and Transition-Metal Nanostructures
International Collaboration Center (ICC-IMR)T

he realization of the nanomaterials with specific topology and supramolecular architecture useful for highperformance nanoscale devices is currently one of the main challenges in nanotechnology. Here we highlight
our recent research activities on inorganic/organometallic functional materials for molecular electronics, lightharvesting and photocatalysis.
Covalent and non-covalent donor−acceptor(D−A) assemblies were intensively studied during
the last several decades due to their potential use insolar energy to electricity conversion. In order toarchive the high efficient solar energy conversion,
the formation and stability of the long-living chargeseparation state, which can be controlled by theelectronic structure, type of the linking group, andgeometric orientation of the light-harvesting donor
and electron acceptor, is required. The D−A
assemblies with covalent bonds can be controlled
by the nature of the linking group.
However, the preparation often requires several
additional synthetic steps, which make such
structures less attractive for industrial applications.
An alternative approach is the formation of wellorganized non-covalent assemblies, which can becontrolled by dispersion interactions.
We have prepared the non-covalent complexes
formed between C60 and C70 fullerenes andsubstituted boron subphthalocyanines (Fig. 1 (A))
and examined the tunability of the subphthalocyanine
core toward finding a stronger binding fullerene
receptor, which improve photovoltaic characteristicsof heterojunctions by facilitating the electron-transferfrom subphthalocyanine to fullerene [1]. It has beenfound that the hexathiophenol-containing receptor
shows the largest interaction energy with fullerenes
that confirmed by UV-vis data (Fig. 1 (B)) andextensive DFT calculations (Fig. 1 (C)).
These systems were thought as a low-cost
alternative to the traditional organic light-harvesting
modules for organic photovoltaics.
New trinuclear Fe−Ru−Fe tetraphenylporphyrin complexes axially coordinated with various
ferrocene-based ligands, were prepared andcharacterized [2]. It was observed that the firstoxidation process was attributed to the reversible
oxidation of the RuII center, which is important for
their application as molecular wires (see Fig. 2).
DFT and time-dependent DFT calculations aided incorrelating the spectroscopic and redox properties

Fig. 1 Non-covalent complex formation in subphthalocyanine/fullerene system.
TPP 2-/TPP 1- FeII/FeIII

II

III

Ru /Ru

e-

FeII

Ru

FeIII

Fig. 2 Trinuclear porphyrin/ferrocene complexes [2].

of studied complexes with their electronic structures.
New spherical organic−inorganic ferrocene-tinhydroxide clusters of general formula [(FcSn)12O14(OH)6]
X2 were prepared and analyzed [3]. DFT and TDDFT
calculations suggest that the organometallic
substituents in the [(FcSn)12O14(OH)6]2+ core are rather
isolated from each other, and thus such a cluster canbe potentially used as an electron reservoir, which canprovide up to 12 electrons toward chemical processes.
References[1] H. M. Rhoda, M. P. Kayser, Y. Wang, A. Y. Nazarenko, R. V.
Belosludov, P. Kiprof, D. A. Blank, and V. N. Nemykin, Inorg.
Chem. 55, 9549 (2016) (Editor's choice paper with front coverpage).
[2] V. N. Nemykin, S. V. Dudkin, M. Fathi-Rasekh, A. D. Spaeth, H.
M. Rhoda, R. V. Belosludov, and M. V. Barybin, Inorg. Chem.
54, 10711 (2015).
[3] P. V. Solntsev, D. R. Anderson, H. M. Rhoda, R. V. Belosludov,
M. Fathi-Rasekh, E. Maligaspe, N. N. Gerasimchuk, and V. N.
Nemykin, Crystal Growth Design 16, 1027 (2016).

Victor Nemykin (Corresponding Author, Department of Chemistry, University of Manitoba, Canada)
E-mail: Viktor.Nemykin@umanitoba.ca
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 201749

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 two neutron spectrometers 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.
Center of Neutron Science for Advanced
Materials (NC-IMR) was established in 2010 with theaim of promoting novel materials science by using
neutrons. The NC-IMR is operating two neutron
instruments at the JRR-3 research reactor in theJapan Atomic Energy Agency and is now
constructing a state-of-the-art polarized neutron
spectrometer, POLANO, with an intense neutron
source at the Materials and Life Science Experimental
Facility (MLF) in the Japan Proton Accelerator
Research Complex (J-PARC) [1]. The constructionof POLANO started in 2012 under the collaboration
with High Energy Accelerator Research Organization(KEK) and has almost completed. The spectrometer
will be offered for the collaborative research
programs of IMR after the commissioning process.
To promote the utilization of neutrons for condensed
matter physics and materials science, we madeleaflets for the advertisement of our spectrometers(Fig. 1) and widely distributed them to the researchgroups in Japan.
Furthermore, to provide an opportunity to theundergraduate students to visit a neutron facility,
NC-IMR held an MLF-JRR3 tour (as a part of theuniversity program “Frontier of Physics”). Six
students of the Department of Physics, Tohoku
University, attended a two-day tour. The staff
members of Tohoku University, KEK, and JAEA
gave lectures on neutron scattering techniques andusage of neutrons for materials science. The
students visited HERMES, which is a powder
diffractometer managed by NC-IMR (Fig. 2), andthe new spectrometer POLANO in MLF. The tour
was well received by the participants.
References[1] T. Yokoo, S. Itoh, N. Kaneko, M. Fujita, T. Ino, M. Ohkawara, K.

Fig. 1 Leaflet of neutron spectrometers, which areoperated by IMR, Tohoku University.

Fig. 2 Group photo of the “Frontier of Physics” workshop
organized by NC-IMR in February 2017.

Ohoyama, and M. Sakaguchi, to appear in J. Phys.: Conf.
(2017).

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/

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IMR KINKEN Research Highlights 2017

Energy-Efficient Electric Motors Made from Nanocrystalline
Soft Magnetic Alloy “NANOMET®”
Research and Development Center for Ultra High Efficiency
Nano-Crystalline Soft Magnetic Materials

A brushless DC motor made from NANOMET core exhibits remarkable improvement in energy consumption.
®

A prototype motor with an outer core diameter of 70 mm and thickness of 50 mm was constructed using thelaminated nanocrystalline soft magnetic alloy (NANOMET®) ribbons.

Nowadays, there is an increasing interest inenergy conservation for preventing the exhaustionof precious minerals and environmental pollution. In
Japan, motors consumed 51 % of the total electricalenergy. Energy loss is especially significant in soft
magnetic silicon-steel cores (~ 2–3 W/kg) used toconstruct motors. Research has shown almost no
improvement in the energy loss properties of Sisteel since the 2000s.
Recently, a series of new nanocrystalline alloys,
NANOMET® [1], were developed. Energy loss inthese alloys is 1/3 of that of oriented Si-steel and isnearly one order of magnitude lower than that of
non-oriented steel, which are generally used tomake motors for consumer goods. The NANOMET®
alloys show high Bs close to that of Si-steel and havethe ability for mass production.
In this article, we advertise the first successful
assembling of a radial-gap type motor (Fig. 1) using
NANOMET® ribbons. Nanocrystalline ribbons ofwidth 80 mm and thickness 30 µm were laminatedin the form of a magnetic core having an outer
diameter 70 mm and a thickness 50 mm, to constructa prototype brushless DC motor. Figures 1 (a) and(b) show the outer appearance of the constructed
stator-core and the completed motor. The prototype
motor using the NANOMET® core exhibits an
outstandingly low core-loss of 0.4 W compared tothat of the motor made with non-oriented Si-steel
core (1.4 W). The reduction in energy loss in thecore was ~ 70%, which is huge. In a directcomparison with the non-oriented Si-steel
commercial motor under the rated testing conditionsof an applied load torque of 80 mN·m and revolutionsof 1920 rpm (revolution per minute), the prototype
motor comprising the NANOMET® core exhibited aremarkable 3% improvement in the overall efficiency.
An overall efficiency improvement of as high as ~6% was recorded for the motor that was constructed
for R&D purpose. The industrial feasibility of theFig. 1 (a) Outer appearance of the constructed stator-coreand (b) the completed brushless DC motor [2].

NANOMET® core for highly energy efficient motors
was thus confirmed.
References[1] A. Makino, H. Men, T. Kubota, Y. Yubuta, and A. Inoue,
Materials Transactions 50, 204 (2009).
[2] N. Nishiyama, K. Tanimoto, and A. Makino, AIP Advances 6,055925 (2016).

Akihiro Makino (Corresponding Author, Professor, New Industry Creation Hatchery Center)
E-mail: nanom@imr.tohoku.ac.jp
URL: http://nanom.imr.tohoku.ac.jp/

IMR KINKEN Research Highlights 201751

Research Centers

Two-Dimensional Superconductivity Maintained in Giant
Magnetic Fields
Laboratory of Low Temperature Materials Science

Recently emerged two-dimensional superconductors have been attracting growing interests due to their

exotic properties. As an example, we present the giant critical magnetic field exceeding 50 T in ion-gated
MoS2, where the superconductivity is protected by spin-orbit interaction originating from the broken inversion
symmetry in the confined geometry.

Two-dimensional (2D) superconductivity inatomically thin layers has become a renewed
research field owing to the recent developments intechnologies for fabricating clean 2D electron
systems such as heterogeneous interfaces, atomic
layers grown by molecular beam epitaxy, exfoliatedthin flakes, and field-effect devices. These systems
are generally highly crystalline, and are promising
for the observation of intrinsic quantum properties,
which are otherwise hidden by disorders in theconventional thin film superconductors [1]. The iongated single crystal surface in the electric double
layer transistor (EDLT), where the electrons arestrongly confined in the topmost layer by electricfield, provides such a clean 2D superconductor [2].
Here, we report the exotic superconductivity in
EDLT of MoS2, which is maintained in a giant
magnetic field exceeding the limit predicted byconventional theory [3].
Figure 1 shows the upper critical magnetic field
Hc2 of a MoS2-EDLT with the critical temperature Tc= 6.5 K at a gate voltage VG = 5.5 V as a function oftemperature T. While Hc2 in the out-of-planecondition is as low as 4 T, that in the in-planecondition increased to approximately 52 T at T = 1.5
K. This value is much higher than the usualparamagnetic limit of 1.86Tc, derived from the BCS
theory. The anomalous enhancement of Hc2 can be
explained based on the crystal structure of the MoS2
monolayer, where the in‑plane inversion symmetryis spatially broken, as shown in the inset of Fig. 1.
This causes a special type of spin-orbit interaction(SOI) that produces out‑of‑plane spin polarization
with the effective Zeeman magnetic fields, and arecalled as the Zeeman-type SOI. In this situation, thesuperconductivity occurs with the Cooper pairsconsisting of upward and downward spins, both ofwhich are aligned along the out-of-plane direction,
resulting in the protection of superconductivity
against the in-plane magnetic field.

MoS2-EDLTVG = 5.5 V

Se
Mo

Fig. 1 The in‑plane and out‑of‑plane upper critical field
Hc2 as a function of temperature T in ion-gated MoS2.
The inset shows the top view of a monolayer MoS2
crystal (Figures are from Ref. 3, Nature PublishingGroup).

According to first-principle calculations, theenergy for the spin polarization is 13 meV, whichindicates that the electrons indeed feel an internal
out‑of‑plane magnetic field of about 100 T; this
explains the experiments well. The above
observation is possible in monolayer limit and highcrystallinity, which are realized in EDLT.
References[1] Y. Saito, T. Nojima and Y. Iwasa, Nat. Rev. Mater. 2, 16094(2017).
[2] Y. Saito, T. Nojima, Y. Iwasa, Supercond. Sci. Technol. 29,093001 (2016).
[3] Y. Saito, Y. Nakamura, M. S. Bahramy, Y. Kohama, J. Ye, Y.
Kasahara, Y. Nakagawa, M. Onga, M. Tokunaga, T. Nojima, Y.
Yanase, and Y. Iwasa, Nat. Phys. 12, 144 (2016).

Tsutomu Nojima (Laboratory of Low Temperature Materials Science)
E-mail: nojima@imr.tohoku.ac.jp
URL: http://ltsd.imr.tohoku.ac.jp/index-e.html
Takahiko Sasaki (Head of Laboratory of Low Temperature Materials Science)
E-mail: ltcenter@imr.tohoku.ac.jp

52

IMR KINKEN Research Highlights 2017

IMR KINKEN Research Highlights 2017

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 over 170
radionuclides (RIs) and elements, especially alpharay emitters such as actinides. This lab functions as
a source for the preparation of pure crystals of
actinide compounds, providing them to otheruniversities and to the Synchrotron Orbital Radiation(SOR) facilities. The Radiation Controlled Area of
this laboratory includes three chemistry labs andthree physical labs, which are equipped with local
exhaust ventilation systems enabling handling ofvarious kinds of materials. Many spectrometers
including those for gamma-rays and alpha-rays areavailable here.
Ultra-low radioactive techniques are studied inthis lab as a key to develop particle and nuclear
physics researches. A large liquid scintillator
detector (KamLAND) in the Kamioka mine wasconstructed for neutrino researches by the ResearchCenter for Neutrino Science in Tohoku University in2002 [1]. However, a further reduction in radioactive
impurities in the liquid scintillator is essential forenhancing its sensitivity to important physicalquantities such as the neutrino masses probed by
the neutrinoless ββ–decay experiments [2]. One ofthe problematic impurities is 210Pb, which resultsfrom a series of 238U that exists in mine rocks.
Although we had once established an excellent
purification method by using a distillation apparatus,
its operation was rather complicated and not costeffective. Thus, as an alternative method, weinvestigated metal scavenging recently developed
in industries [3,4].
For the Pb removal test, 220Rn emanating froman intense ThO2 source was dissolved in the liquid
scintillator with nitrogen purging, and daughter
212Pb were accumulated. Among the 12 candidatesof metal scavengers, R-Cat-Sil AP (Kanto ChemicalCo., Inc.), which attained about 98% efficiency inlinear alkylbenzene used as a liquid scintillator
component (Fig. 1), proved to be the best for 212Pb

Metal scavenging process

NH2

M

+

NH2

M

KamLAND
neutrinoless ββ-decay
eeν

n

ν

n

Fig. 1 Removal efficiency of 212Pb in linear alkylbenzene
as a function of the number of cycles in the metal
scavenging process under optimized parameters. The
red line indicates the fitted curve, assuming an
exponential reduction in 212Pb with a constant term.

removal.
Metal scavenging was found to be a practicalmethod for Pb removal, which does not require acomponent change of the liquid scintillator. We
confirmed that the emanated 222Rn is consistent
with the background level, which indicates that the
scavenging process did not newly introduce 210Pb
in the liquid scintillator. This ensured the reduction of
210 Pb, leading to a significant improvement in theneutrino mass sensitivity of KamLAND.
References[1] K. Eguchi et al., Phys. Rev. Lett. 90, 021802 (2003).
[2] A. Gando et al., Phys. Rev. Lett. 117, 082503 (2016).
[3] A. Hinchcliffe, C. Hughes, D. A. Pears, and M. R. Pitts, Org.
Process Res. Dev. 11, 477 (2007).
[4] O. Chkvorets, R. Ford, D. Hallman, and E. Vázquez-Jáuregui
Nucl. Phys. Proc. Suppl. 229, 519 (2012).

Tomoo Yamamura (Head of Laboratory of Alpha-Ray Emitters)
E-mail: yamamura@imr.tohoku.ac.jp
URL: http://alpha.imr.tohoku.ac.jp

IMR KINKEN Research Highlights 201753

Research Centers

Extensive Application of Cs-Corrected TEM and STEM for
Materials Characterization
Analytical Research Core for Advanced Materials (ARCAM)

Recently, a most-advanced scanning transmission electron microscope ((S)TEM) has been installed in

ARCAM. This instrument is equipped with two Cs-correctors and high performance EDS and EELS systems.
High quality data can be obtained easily and quickly from this upgradation. Furthermore, advanced applications
such as the direct observation of atomic columns and local state analysis at atomic scale can be performed.

We demonstrate the microstructural analysis of
a novel CuMnAlFe shape memory alloy (SMA) [1].
Although the conventional TEM (CTEM) observations
revealed that the crystal structure of the matrix isL21–type, and the precipitates have bcc-basedordered structure and cuboidal shape with grain
sizes from sub-micron to around 10 nm, it wasdifficult to distinguish the detailed chemical-orderedstructure of the precipitate by the electron diffraction
technique. Moreover, the analysis function of theexisting TEM is only a single point EDS measurementwith a spatial resolution of up to 20 nm. Hence, the
new STEM was employed for further investigations.
Small coherent precipitates with grain sizes ofaround 10 nm could be seen using the advanced
STEM (Fig. 1 (a)), which otherwise require a carefulobservation using CTEM. This clearly demonstrates
that these precipitates contain high concentrationsof Fe and Mn and no Cu. Since the HAADF-STEM
images exhibit strong atomic number (Z) contrasts,
as shown in Fig. 1 (b), it is suggested that the brightspots represent the Fe and Mn columns, whereas
the dark ones represent the Al columns. Therefore,
the crystal structure of the precipitates wasconsidered as the D03 -type.
Figure 2 shows an example of EELS
measurement of a titania nanomaterial [2]. The
spectrum was acquired in the Ti-L region, where
crystal-field splitting was clearly observed. The finestructure in the spectrum provides useful informationsuch as the bonding state, valence state, andcoordination environment. We support EELS
characterization using (S)TEM equipped with a cold
field-emission electron gun, which enables
measurements with a high energy resolution.

Fig. 1 (a) EDS mapping of CuMnAlFe SMA. (b) High angle
annular dark field (HAADF)-STEM image of the Fe-richprecipitate.

Fig. 2 An example of EELS measurement of Ti-L edge of atitania nanomaterial.

References[1] S.Y. Yang, T. Omori, C.P. Wang, Y. Liu, M. Nagasako, J.J.
Ruan, R. Kainuma, K. Ishida, and X.J. Liu, Sci. Rep. 6, 21754(2016).
[2] M. Ohwada, K. Kimoto, Y. Ebina, and T. Sasaki, Microscopy
64, 77 (2015).

Makoto Nagasako (Corresponding Author, Analytical Research Core for Advanced Materials)
E-mail: nagasako@imr.tohoku.ac.jp
Megumi Ohwada (Corresponding Author, Analytical Research Core for Advanced Materials)
E-mail: ohwada.megumi@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/

54

IMR KINKEN Research Highlights 2017

Author Index
NamepageNamepageA

Mizuguchi, MasakiAkiyama, Eiji

9Araki, Yasufumi

26

Arima, Hiroshi

34

B
Bauer, Ernst-Wilhelm Gerrit

49

C

Mohri, Tetsuo

23, 47

N
Nagai, Yasuyoshi

32, 42, 43

Nagasako, Makoto

54

Nemykin, Victor

49

Nojima, Tsutomu

52

Nojiri, Hiroyuki

Chen, Ying

47

Chiba, Akihiko

11

F

48

27, 45O
Ohno, Yutaka

17

Ohwada, Megumi

54

Fujita, Masaki

50

Okada, Junpei

37

Fujiwara, Kohei

29

Orimo, Shin-ichi

21, 48

Fujiwara, Kozo

16

Furuhara, Tadashi

44

S
Sasaki, TakahikoGGoto, Takashi

10

H30, 52

Sato, Toyoto

21

Satoh, Yuhki

19

Semboshi, Satoshi

46

Shiba, Hayato

23

Hirobe, Daichi

28

Shimizu, Yasuo

32

Honda, Fuminori

39

Shimizu, Yusei

43

Shiogai, Junichi

29

Sugiyama, Kazumasa

34

I
Ikeda, Yoichi

31

Inoue, Koji

32

K
Kashiwakura, Shunsuke

13

Kato, Hidemi

20TTakanashi, Koki

36

Taniguchi, Kouji

35

Toyama, Takeshi

42

Katsui, Hirokazu

10, 22

Kimura, Shojiro45

Uda, Satoshi

37

Konno, J. Toyohiko

12

Umetsu, Y. Rie

44

Kubo, Momoji

18

U

W
M

Wagatsuma, Kazuaki

54

Makino, Akihiro

51

Masahashi, Naoya

46

YMatsuoka, Takashi

33

Yamada, Ryo47

Miyamoto, Goro

8

Yamamura, Tomoo

53

Miyasaka, Hitoshi

35

Yoshikawa, Akira38

IMR KINKEN Research Highlights 201755

Keyword Index
Keywordpage

KeywordpageA

molecular devices 35

age-hardening12

molecular dynamics

18

alloy amorphous 

1123, 37

nanostructure 

20, 32

atom probe tomography

32

neutron scattering 27

aluminum alloys

12

nitride 

33

nuclear materials 

19nucleation & growth 

8C
ceramic chemical vapor deposition (CVD)

18
10, 22O

corrosion 

9organic 30

crystal growth 

16oxide 29

D

P

deformation 

11parity symmetry breakingdomain wall

26

phase transformation 

doping 

35

porosity 

E

31
8, 12
20

Q

electrical properties 30, 39electron irradiation 

19

Selectronic material 

32

scintillator38

energy storage 21simulation quantum spin system

28

18,19, 23

eutectics38

Si37

F

sintering 

10solar cells

16,17

field-effect transistor

29

foam20

spectroscopy13

G

spin dynamics

36

grain boundaries

17

spintronics

Goldschmidt tolerance factor

21

steel826, 28structure34

H
heavy fermion31

supercooled liquid

37high magnetic field

27

surface reaction

9high pressure

39

Thigh strength steel

9thin films

29, 33hydride21

tourmaline34

I

Vionic conductor

22L
laser plasma

13valence transition

39

vapor phase epitaxy (VPE)

33

W
Weyl semimetalM

26

magnetic

28, 31X

magnetic properties

35, 36

XAFS34

mechanical properties metal-insulator transition 
microstructure 56

N

IMR KINKEN Research Highlights 201723

X-ray scattering

27

30

X-ray imaging38

10, 11, 22

Editors
Atsushi Tsukazaki, Gerrit E.W. Bauer,
Kozo Fujiwara, Yusuke Nambu,
Junpei Okada, and Shigeyuki Takagi

Editorial Staff
Misa Yokoyama, Aki Oikawa, and Izumi Suda

Printing
HOKUTO Corporation

Organization
Institute for Materials Research
Tohoku University
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