KINKEN
Research Highlights
2016

Institute for Materials Research, Tohoku University

KINKEN Research Highlights 2016
Contents
Preface .......................................................................................................................................................... 4

Research Highlights

1. Infrastructural Materials
Microstructure Design of Structural Metallic Materials Division .................................................................... 8
Chemical Physics of Non-Crystalline Materials Division .............................................................................. 9
Biomaterials Science Division .................................................................................................................... 10
Advanced Crystal Engineering Laboratory .................................................................................................11
Multi-Functional Materials Science Division ............................................................................................... 12
Deformation Processing Division ............................................................................................................... 13
Analytical Science Division ........................................................................................................................ 14
Advanced Materials Development andIntegration of Novel Structured Metallic and Inorganic Materials .................................. 15
Computational Materials Research Initiative (CMRI) ................................................................................. 16

2. Energy-related Materials
Crystal Physics Division ............................................................................................................................. 18
Materials Design by Computer Simulation Division .................................................................................... 19
Irradiation Effects in Nuclear and Their Related Materials Division ............................................................ 20
Nuclear Materials Science Division ........................................................................................................... 21
Nuclear Materials Engineering Division...................................................................................................... 22
Non-Equilibrium Materials Division ............................................................................................................. 23
Hydrogen Functional Materials Division ..................................................................................................... 24

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
Physics of Crystal Defects Division ............................................................................................................ 32
Physics of Electronic Materials Division .................................................................................................... 33
Solid-State Metal-Complex Chemistry Division .......................................................................................... 34
Magnetic Materials Division........................................................................................................................ 35
Crystal Chemistry Division ......................................................................................................................... 36
Actinide Materials Science Division ........................................................................................................... 37
Materials Science of Non-Stoichiometric Compounds Division ................................................................. 38

Research Centers
International Research Center for Nuclear Materials Science .................................................................... 40
Cooperative Research and Development Center for Advanced Materials ................................................ 42
High Field Laboratory for Superconducting Materials................................................................................ 43
Kansai Center for Industrial Materials Research ........................................................................................ 44
Center for Computational Materials Science .............................................................................................. 45
Collaborative Research Center on Energy Materials .................................................................................. 46
International Collaboration Center (ICC-IMR)............................................................................................. 47
Center of Neutron Science for Advanced Materials ................................................................................... 48
Research and Development Centerfor Ultra High Efficiency Nano-Crystalline Soft Magnetic Material ................................ 49
Laboratory of Low-Temperature Materials Science .................................................................................... 50
Laboratory of Alpha-Ray Emitters .............................................................................................................. 51
Analytical Research Core for Advanced Materials ..................................................................................... 52

Author Index ............................................................................................................................................... 53

Keyword Index ........................................................................................................................................... 54

Preface

Dear Colleagues,

We are pleased to present KINKEN Research Highlights 2016, 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.

We are happy to say that IMR celebrates its centenary this year. Professor Kotaro Honda establishedthe IMR at the Tohoku Imperial University in 1916 as the 2nd Division of the Provisional Institute ofPhysical and Chemical Research. At that time the primary research focus was steel. Thereafter, theresearch domains gradually broadened to include various types of alloys and metals. The name waschanged into the Research Institute for Iron, Steel and Other Metals (RIISOM) in 1922. Subsequently, theinstitute developed into a global center for fundamental and applied research covering all types ofmaterials, 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 forMaterials 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 for4

IMR KINKEN Research Highlights 2016

Director

materials development, which paved the way for pioneering research in magnetism, superconductivity,
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 2016

5

Infrastructural Materials

IMR KINKEN Research Highlights 2016

Infrastructural Materials

Enhanced Surface Hardening in Nitriding Process by Dynamic
Provision of Nucleation Site For Alloy Nitride Precipitation

Higher surface hardness is required for machinery parts to ensure high reliability and longer life. We foundthat the combined addition of vanadium and aluminum to iron for nitriding treatment resulted in a significant
increase in surface hardness because the vanadium–nitrogen atoms form fine clusters in the early stage andaluminum nitride precipitation is enhanced by the nucleation at the cluster.

Machinery parts such as gears and shafts
require high toughness, as well as high hardness,for resistance to wear and fatigue. However, ingeneral, those properties cannot be improved
simultaneously.
Therefore,
surface-hardening
processes are performed to harden only the surface
region, while the inward region remains ductile.
Nitriding is one of the most popular surfacehardening treatments for steel, which improves
fatigue-, wear- and corrosion-resistant properties.
As compared to other surface-hardening processes,
nitriding has advantages in terms of small distortion
during the process, higher surface hardness, andbetter softening resistance at elevated temperatures.
The process has thus attracted much attention forthe surface hardening of high-precision parts. In the
nitriding process, steel parts are held at 500–600°C
in a nitriding atmosphere so that nitrogen atoms areabsorbed from the surface and then diffuse inward.
Surface hardening by nitriding is caused mainly by
precipitation of fine alloy nitrides or of alloying
element (M)–nitrogen (N) clusters near the surface.
Therefore, an understanding of alloy nitride
precipitation behavior is crucial to controllingsurface hardening by nitriding.
In order to clarify alloying effects on the
precipitation of alloy nitrides and the resultant
surfacehardening,
weinvestigatedthemicrostructure and surface hardness of various
nitrided Fe–M binary alloys [1]. It was found thatnano-sized M–N clusters formed in the nitriding of
Fe–V or Fe–Ti alloys, whereas no precipitation of Al
nitrides was observed [1]. As a result, the Fe–Al
alloy did not show surface hardening as comparedto the other alloys, as shown in Fig. 1 (top). Because
Al is also a strong nitride-forming element, its
precipitation should be facilitated by introducing
nucleation sites.
Recently, we investigated the effects of the
combined addition of Al and V atoms, and we foundthat the addition of V to Fe–Al alloys significantly
accelerated the precipitation of Al nitrides, resulting

Fig. 1 (top) Hardness–depth profiles of the specimen
nitrided at 550°C for 16 h, (bottom left) TEM images ofprecipitates in Fe–1Al and Fe–1Al–0.5V alloys, and(bottom right) schematic illustration of nucleation of Al
nitride at the V–N cluster.

in significant surface hardening [Fig. 1 (top)].
Because the V–N attractive interaction is muchstronger than the Al–N one, the formation of V–Nclusters take place first, and then precipitation of Al
nitrides is induced by nucleation at the V–N cluster/matrix interface at the growth front of the nitrided
region [Fig. 1 (bottom)]. Consequently, such
dynamic provision of nucleation sites during thenitriding process was found to be very effective forenhanced surface hardening.
References[1] G. Miyamoto, Y. Tomio, H. Aota, K. Oh-ishi, K. Hono, and T.
Furuhara, Mater. Sci. Technol., 27, 742 (2011).
[2] G. Miyamoto, S. Suetsugu, K. Shinbo, and T. Furuhara, Metall.
Mater. Trans. A, 46A, 5011 (2015).

Keywords: steel, atom probe tomography, nanocluster
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

8

IMR KINKEN Research Highlights 2016

IMR KINKEN Research Highlights 2016

Local Structure around Ge in Lithium– Germanate GlassesT

he local structure around Ge in lithium–germanate glasses was investigated by using the anomalous X-ray
scattering technique. The averaged coordination number of the first neighboring Ge–O pair increased withincreasing Li2O content up to 24 mol%. The introduction of an octahedral GeO6 unit is one of the mostfundamental structural changes accompanying the so-called germanate anomaly detected in density
measurements.
The densities of lithium–germanate glasses
show a maximum value at approximately 20 mol%
Li2O [1, 2]. Because the physical properties ofglasses correlate with their atomic structures, several
advanced analytical studies have been applied for
elucidating the structural model for this interesting
behavior. We investigated the local structure aroundGe in lithium-germanate glasses using anomalous
X-ray scattering (AXS) measurements, which isranked as the most advanced method currently
available for obtaining quantitative local structural
information for glasses [3].
Lithium–germanate glass samples wereprepared by an ordinary melt–quench technique.
Powder mixtures of GeO2 (99.99%) and Li2CO3(99.0%) were calcined at 923 K for 1 h. The preparedsamples were melted in a platinum crucible in air for
1 h at 1673 K, and then the melts were quenched bypressing them between two copper plates. The AXS
measurements at the Ge K absorption edges were
performed at the BL-7C beamline of the Photon
Factory at the Institute of Material Structure Science,High Energy Accelerator Research Organization.
Figure 1 shows the ∆QiGe(Q) profiles [4] of four
lithium–germanate glasses. Significant differences
are observed at the first peak region of approximately
1.8 Å-1, and the peaks decrease and broaden as the
Li2O content increases. Because the first peak is
associated with the structure of Ge–Ge pairs, thechange detected in the ∆QiGe(Q) profiles suggests
the possible breakdown of the network structurecomposed of GeO4 tetrahedra.
The environmental RDFs for Ge calculated by
Fourier transformation of the ∆QiGe(Q) profiles
indicated that the distance of the Ge–O pairs
increased with increasing Li2O content. Thissuggests the introduction of a new local structuralunit of GeO6, as shown in a previous work. Further
analysis showed that the fraction of GeO6 in thelithium–germanate
glassesincreasedwithincreasing Li2O content up to 24 mol%. This variation
in local structural unit produced a slightly different

Fig. 1 shows environmental interference functions of xLi2O– (1 – x)GeO2 glasses.

behavior, which was suggested originally by thedensity measurements. Nevertheless, a similarsuggestion was also reported by Henderson andFleet [5] through a discussion of the observedchange in Ge–O distances.
References[1] A. O. Ivanov and K. S. Evstropiev, Dokl. Akad. Nauk SSSR
145, 797 (1962).
[2] M. K. Murthy and J. Ip, Nature 201, 285 (1964).
[3] Y. Waseda, E. Matsubara, and K. Sugiyama, Sci. Rep. RITU
A34, 1 (1988).
[4] H. Arima, T. Kawamata, and K. Sugiyama, J. Min. Pet. Sci.
110, 60 (2015).
[5] G. S. Henderson and M. E. Fleet, J. Non-Cryst. Solids. 134,
259 (1991).

Keywords: glass, anomalous X-ray scattering, XAFS
Hiroshi Arima and Kazumasa Sugiyama (Chemical Physics of Non-Crystalline Materials Division)
E-mail: arimah@imr.tohoku.ac.jp
URL: http://www.xraylab.imr.tohoku.ac.jp/

IMR KINKEN Research Highlights 20169

Infrastructural Materials

Effect of Solid-solute Oxygen Addition on Wear Properties ofBiomedical Ti–29Nb–13Ta–4.6Zr Alloy

Ti–29Nb–13Ta–4.6Zr alloy (TNTZ) exhibits good biological and mechanical compatibilities owing to its low

toxicity and the fact that its Young’s modulus is close to that of human bone (approximately 60 GPa). Although
the wear resistance of titanium alloys is generally poor as a biomaterial, the mechanical strength of TNTZ canbe improved by adding an interstitial element, oxygen (O). Thus, the wear characteristics of TNTZ with different
oxygen contents were investigated. The volume loss of TNTZ with high O content was significantly lower thanthat of TNTZ with low O content. Therefore, it is concluded that solid-solution strengthening by oxygen increases
the wear resistance of TNTZ.

Wear resistance is one of the most importantmaterial properties for biomedical devices withmetal-to-metal contact parts because failure caneasily occur at such contact parts.
The wear behaviors and mechanisms of two
types of titanium alloys were previously analyzed
and compared both in air [1] and in Ringer’s solution[2]. The first alloy was a conventional (α + β)-type
Ti–6Al–4V extra-low-interstitial (Ti64) alloy; thesecond was a newly developed β-type Ti alloy forbiomedical applications, Ti–29Nb–13Ta–4.6Zr(TNTZ). It was concluded that volume losses (Vloss)of the TNTZ discs and balls were larger than thoseof the respective Ti64 discs and balls, both in air
and in Ringer’s solution. Particularly, when the TNTZ
disc slid against the TNTZ ball, Vloss of both the discand ball exhibited maximum values both in air andin Ringer’s solution. These results are related to thesevere subsurface deformation of TNTZ, which is
caused by the lower resistance of TNTZ to plastic
shearing than Ti64, inducing delamination andresulting in a higher wear rate.
Therefore, it is necessary to increase the wear
resistance of TNTZ while keeping its Young’s modulus
similar to that of human bone. Young’s modulus isrelated to the crystal structure, which remains
essentially unchanged with increasing interstitial
element content. Thus, interstitial elements are very
promising because their addition to TNTZ is expected
to improve its plastic shear resistance via solution
strengthening. The wear behavior of TNTZ withoxygen contents of 0.06 and 0.89 mass% (06O and
89O, respectively) were investigated in this study.
The Vickers hardness values of discs and balls
made of Ti64, 06O, and 89O were measured. The
hardness of the 89O discs was higher than that of
the Ti64 discs. Moreover, the hardness of the 89Oballs was higher than that of the Ti64 balls. In thecase of the 06O material, the hardness of both discs
Keywords: alloy, biological, mechanical properties
Mitsuo Niinomi (Biomaterials Science Division)
E-mail: niinomi@imr.tohoku.ac.jp
URL: http://biomat.imr.tohoku.ac.jp/

10

IMR KINKEN Research Highlights 2016

Fig. 1 Volume losses of (a) Ti64/06O combinations and (b)Ti64/89O combinations during frictional wear tests in
Ringer's solution.

and balls was lower than that of the respective Ti64
and 89O discs and balls.
The Vloss values of discs and balls made of
Ti64, 06O, and 89O subjected to frictional wear
tests in Ringer’s solution are shown in Fig. 1. The
Vloss values of the 89O discs and balls are much
lower than those of the 06O discs and balls,
regardless of the mating materials. The increase inhardness improved the plastic shear resistance of
the 06O discs and balls, which is necessary to avoid
severe delamination wear. Therefore, it can beconcluded that solid-solution strengthening is avery effective treatment for improving the wear
resistance of TNTZ biomedical implants.
References[1] Y.-S. Lee, M. Niinomi, M. Nakai, K. Narita, and K. Cho, J.
Mech. Behav. Biomed. Mater. 41, 208 (2015).
[2] Y.-S. Lee, M. Niinomi, M. Nakai K. Narita, and K. Cho, Mater.
Trans. 56, 317 (2015).

IMR KINKEN Research Highlights 2016

Development of Eu:SrI2 Scintillator Single Crystal and Gammaray Detection Devices Using the Eu:SrI2 Bulk Single Crystal

High-light-yield and high-energy-resolution Eu:SrI gamma-ray scintillator single crystals were developed
2

using a modified micro-pulling-down (µ-PD) method. In addition, Eu:SrI2 bulk single crystals with diameters of
1–2 in. were grown by a modified Bridgman method using a modified µ-PD furnace. Gamma-ray detection
devices using the Eu:SrI2 bulk single crystal, such as a spectrometer were also developed.

Halide (chloride, bromide, and iodide) materials
were investigated owing to their significant potential
as scintillator materials with high light yield and highenergy resolution. Halide materials have relatively
small band-gaps as compared to oxides andfluorides, and the high light yield of halide materials
is attributable to this small band-gap. In addition,
the high light yield provides high-energy resolution.
However, most halide materials have strong
hygroscopicity, and it is difficult to grow high-quality
and high-transparency single crystals.
Therefore, we developed a modified micropulling-down (µ-PD) method for the crystal growthof halide materials [Fig. 1(a)] [1]. In the modifiedµ-PD method, a removable chamber that can beentered through a glove box filled with high-purity Ar
gas is used, thus protecting the inside of thechamber from exposure to outside atmosphere.
Therefore, the modified µ-PD method can be used
to grow single crystals of halide materials without
being affected by outside atmosphere.
Using the modified µ-PD method, we grew
Eu:SrI2 single crystals with high transparency. The
light yield and energy resolution were also muchhigher than those of previous scintillator materials [2].
In addition, we developed a modified Bridgman
method using the modified µ-PD furnace for thegrowth of bulk single crystals because the modifiedµ-PD method can grow only fiber single crystals. By
the modified Bridgman method, we obtained 1 in.
Eu:SrI2 bulk single crystals with various Eu
concentrations [3]. By further optimization of thegrowth conditions, we grew 1.5 and 2 in. Eu:SrI2
bulk single crystals through collaboration with C&A
Corporation [4]. We then developed radiation
devices using the bulk Eu:SrI2 single crystal by the
JST project.
Especially, a handheld high-performance
spectrometer using the Eu:SrI2 bulk single crystal
was developed in collaboration with Chiyoda
Technology Corporation [Fig. 1(b)].

(a)

(b)

Fig. 1 (a) Schematic of the modified µ-PD method. (b)Spectrometer using Eu:SrI2 bulk single crystal.

References[1] Y. Yokota, N. Kawaguchi, K. Fukuda, T. Yanagida, A.
Yoshikawa, and M. Nikl, J. Cryst. Growth 318, 908 (2011).
[2] Y. Yokota, K. Nishimoto, S. Kurosawa, D. Totsuka, and A.
Yoshikawa, J. Cryst. Growth 375, 49 (2013).
[3] Y. Yokota, S. Kurosawa, K. Nishimoto, K. Kamada, and A.
Yoshikawa, J. Cryst. Growth 401, 343 (2014).
[4] Y. Yokota, T. Ito, S. Yasuhiro, S. Kurosawa, Y. Ohashi, K.
Kamada, and A. Yoshikawa, IEEE Trans. Nucl. Sci. (2016)
accepted.

Keywords: crystal growth, devices, radiation effects
Akira Yoshikawa (Advanced Crystal Engineering Laboratory)
E-mail: yoshikawa@imr.tohoku.ac.jp
URL: http://yoshikawa-lab.imr.tohoku.ac.jp/index-e.html

IMR KINKEN Research Highlights 201611

Infrastructural Materials

Fine-Structured High-Temperature Non-Oxide Ceramics by Phase
Decomposition via Spark Plasma Sintering and Heat Treatment

Transition-metal non-oxide ceramics are promising as ultra-high-temperature ceramics and high-hardness
cutting tools. We synthesized dense compacts from Ti- and Zr-based carbide powders by spark plasma
sintering, and nano–submicron-sized fine structures were assembled by the subsequent heat treatment. The
formation of the self-assembled microstructures enhanced the hardness and toughness.

Ti- and Zr-based non-oxide materials such as
TiC, ZrC, TiN, and ZrN have been receiving muchattention for use in extremely severe environments,
e.g., ultra-high temperature ceramics and cutting
tools, because of their high melting point, excellent
corrosion resistance, and high hardness. However,for practical use in industry, low sinterability andfracture toughness should be improved. It is difficult
to consolidate Ti- and Zr-based non-oxide powders
into dense compacts using conventional sintering
techniques. In general, a small amount of metals
such as Ni and Co is added to promote sintering;
however, the metal additives degrade the mechanicalproperties and corrosion resistance of Ti and Zr
carbides. As the powder manufacturing of non-oxide
ceramics has developed, it has been of great interest
to consolidate pure non-oxide powders and to design
dense and high-strength bulk materials by controllingthe micro- and nanostructures.
Spark plasma sintering (SPS) is a novel
technique to quickly consolidate non-oxide ceramic
powders at high temperatures. We consolidated
TiC–ZrC composites from TiC and ZrC powders by
SPS at sintering temperatures up to 2473 K. At hightemperatures above 2273 K, (Ti, Zr)C solid solutions
were formed with a fully dense and uniform
morphology. Because these dense sintered bodies
are pure non-oxide Ti–Zr carbides with no metal
sintering additives, the Vickers hardness reached
26 GPa [1, 2]. The sintered bodies of the (Ti, Zr)C
solid solutions decomposed into Zr-rich and Ti-richphases by the subsequent heat treatment at
temperatures lower than the sintering temperature(1573–2273 K) [3]. The phase decomposition resulted
in the formation of fine nodular structures several
tens to hundreds of nanometers in length, with thecoherent crystal orientation relationship of the TiCrich phase {100}//ZrC-rich phase {100}, as shown in
Figs. 1(a) and (b). By detailing the effects of TiC–ZrC
compositions and heat-treating conditions on thedecomposition behavior, we discovered a variety ofFig. 1 Phase-decomposed microstructures of TiC–ZrC
composites prepared by SPS and the subsequent heat
treatment. (a): Fine nodular structure composed of Tirich (bright contrast) and Zr-rich (dark contrast) solid
solutions. (b): TEM bright-field image and electron
diffraction pattern of the several tens of nanometers
nodular structure. (c) and (d): Nodular structure andlabyrinth structure.

microstructures formed by self-assembling via
eutectoid reactions and spinodal decomposition, as
shown in Figs. 1(c) and (d). The formation of the finemicrostructure enhanced the hardness and fracture
toughness [4].
References[1] Y. Li, H. Katsui, and T. Goto, Key. Eng. Mater. 616, 52 (2014).
[2] Y. Li, H. Katsui, and T. Goto, Ceram. Int. 41, 7103 (2015).
[3] Y. Li, H. Katsui, and T. Goto, Ceram. Int. 41, 14258 (2015).
[4] Y. Li, H. Katsui, and T. Goto, J. Eur. Ceram. Soc. (2016) inpress.

Keywords: ceramic, nanostructure, mechanical properties
Takashi Goto, Hirokazu Katsui and Akihiko Ito (Multi-Functional Materials Science Division)
E-mail: goto@imr.tohoku.ac.jp
URL: http://www.goto.imr.tohoku.ac.jp/

12

IMR KINKEN Research Highlights 2016

IMR KINKEN Research Highlights 2016

Regulating the Coarsening of γ′ Phase in Superalloys

Stabilizing the γ′ phase represents one of the key challenges in developing next-generation superalloys. We

fabricated a cobalt-based superalloy with a nanoscale coherent γ′ phase, (Ni,Co)3(Al,Ti,Nb), isolated bystacking-fault ribbons in the alloy matrix as a result of Suzuki segregation of the alloying atoms. This newnanostructure can reduce the coarsening rate of the γ′ phase at high temperatures.

One key to preserving the large density of thenanoscale γ′ phase while inhibiting its coarsening athigh temperatures is to single out an ideal
microstructure that can effectively reduce thediffusion among γ′-phase particles without
sacrificing the strength of the superalloy. The
formation of planar stacking-fault ribbons insuperalloys as a result of Suzuki segregation of thealloying elements may fulfill this role.
Here, we developed a new cobalt-based
superalloy comprising 35% Ni, 17.5% Cr, 8% Mo,
3% Nb, 2% Al, and 0.8% Ti (mass%) [1]. After coldswaging, the alloy was subjected to aging at 1073 K
for 3 h. The nanoscale γ′-phase particles precipitatedin the γ matrix [Fig. 1 (a)], whereas the stacking-fault
ribbons were formed because of Suzuki segregationof the alloying elements (e.g. Mo and Cr) into theseplanar defects [2, 3] [Fig. 1 (b)]. The enriched soluteatoms (Suzuki segregation) hampered the diffusionof the major elements of the γ′ phase (Ni, Al, etc.)
across these planar defects, thereby isolating
individual γ′-phase nanoparticles and reducing thecoarsening rate of the γ′ particles during hightemperature exposure [Figs. 1 (c) and (d)].
Furthermore, Suzuki segregation of alloying
elements itself can serve as an important additional
factor in strengthening superalloys at elevatedtemperatures (e.g. 973 K).
The developed cobalt-based superalloy
demonstrated an extremely high strength of 1250
MPa at 973 K, as indicated in Fig. 2. As compared
to commercial superalloys (e.g. Waspaloy®), thedeveloped alloy showed higher yield stress both atroom temperature and at elevated temperatures(Fig. 2). Therefore, the present strategy opens a new
avenue in producing superalloys with extremely
high structural stability at high temperatures andexceptional mechanical properties. In addition, thepresent alloy showed excellent cold workability.
Thus, the application of this method in various
structural applications, including heat-resistantsprings, is expected.

Fig. 1 (a) The morphology of γ′ phase in cold-swage alloy
after aging, (b) stacking-fault ribbons, (c) themorphology of γ′ phase after aging for 2000 h, and (d)the LSW relationship of the coarsening γ′ phase [1].

Fig. 2 The temperature dependence of yield stress of thepresent alloy (S66AG) [1]. The results are compared tothose of commercial superalloys such as TMW-4, In718,
Waspaloy®, and so on.

References[1] H. Bian, X. Xu, Y. Li, Y. Koizumi, Z. Wang, M. Chen, K.
Yamanaka, and A. Chiba, NPG Asia Mater. 7, e212 (2015).
[2] Y. Koizumi, T. Nukaya, S. Suzuki, S. Kurosu, Y. Li, H.
Matsumoto, K. Sato, and A. Chiba, Acta Mater. 60, 2901 (2012).
[3] A. Chiba and M. S. Kim, Mater. Trans. 42, 2112 (2001).

Keywords: alloy, nanostructure, mechanical properties
Akihiko Chiba (Deformation Processing Division)
E-mail: a.chiba@imr.tohoku.ac.jp
URL: http://www.chibalab.imr.tohoku.ac.jp/

IMR KINKEN Research Highlights 201613

Infrastructural Materials

Distinguishing Rare-earth Magnets Utilizing Portable
Cathodoluminescence Spectrometer

We report a method to distinguish neodymium–iron–boron (NdFeB) and samarium–cobalt (Sm–Co) magnets
using a portable cathodoluminescence (CL) spectrometer that we realized. Luminescence owing to the NdFeB
and Sm–Co magnets was detected by capturing CL images of vacuum-dried residues of respective solutions
containing the dissolved NdFeB and Sm–Co magnets. Their luminescent colors were different. Thus, it ispossible to distinguish between NdFeB and Sm–Co magnets by obtaining their CL images.

Neodymium–iron–boron (NdFeB) magnets
have been used in various products such as electricvehicles and hard disk drives. Among rare-earth
elements contained in NdFeB magnets, neodymium,dysprosium, and terbium are expected to be in short
supply because of increasing demand. Thus, in thenear future, it is expected that these rare-earth
elements will need to be recovered from the existing
stock of various kinds of magnets. Separation of
NdFeB magnets from other magnets such as
samarium–cobalt (Sm–Co) magnets is the first stepin the recovery process. In the present study, we
report a method to distinguish between NdFeB andSm–Comagnetsusingaportablecathodoluminescence (CL) spectrometer that we
previously realized [1-3]. The portable CL
spectrometer detects luminescence emitted frominsulating materials or semiconductors by thebombardment of electrons.
Figure 1 (a) shows a schematic of the portable
CL spectrometer. The sample was bombarded withfocused electrons by changing the temperature of apyroelectric crystal of LiTaO3 on which a gold wire
was placed at 1 Pa. The luminescence of the sample
was detected through a glass viewport using acommercially available camera whose built-in
infrared filter was removed. The NdFeB and Sm–Co
magnets were each dissolved in hydrochloric acid.
Then, the iron in the solutions was removed using
methyl isobutyl ketone, and the resulting solutions
were dried in vacuum. The dried residues wereused as samples.
Figures 1 (b) and (c) show CL images of thedried residues of the Sm–Co and NdFeB magnets,
respectively, obtained with the portable CL
spectrometer. The dried residue of the Sm–Co
magnet produced orange luminescence. This color
originated from the luminescent color of thesamarium chloride, which has strong peaks at 597
and 647 nm. The dried residue of the NdFeB

Fig. 1 (a) Schematic of a portable CL spectrometer. CL
images of vacuum-dried residues of (b) Sm–Co magnet
and (c) NdFeB magnet.

produced blue.
This luminescence was detected through afilter cut light with wavelengths less than 780 nm.
Thus, this color was ascribed from the infrared
luminescence of neodymium chloride, whose
strongest peaks occur at 878 and 892 nm. The
portable CL spectrometer can therefore distinguishbetween NdFeB magnets and Sm–Co magnets by
the luminescent colors of their CL images.
References[1] S. Imashuku and J. Kawai, Microsc. Microanl. 21(S3), 793(2015).
[2] S. Imashuku, I. Ohtani, and J. Kawai, Proceedings of ALC ’15,
27p-P-48 (2015).
[3] S. Imashuku, K. Wagatsuma, and J. Kawai, Microsc. Microanl.
22, 82 (2016).

Keywords: electron irradiation, spectroscopy, cathodoluminescence
Susumu Imashuku (Analytical Science Division)
E-mail: susumu.imashuku@imr.tohoku.ac.jp
URL: http://wagatsuma.imr.tohoku.ac.jp/

14

IMR KINKEN Research Highlights 2016

IMR KINKEN Research Highlights 2016

Biocompatibility of Ni- and Be-free Ti-based Bulk Metallic Glasses

Ti-based (Ti–Zr–Cu–Pd–Sn) bulk metallic glasses (BMGs) exhibited significant glass-forming ability, highstrength, high thermal stability, low stress corrosion cracking susceptibility, and good bioactivity. In vivo implantevaluation showed that it had good tissue compatibility, equivalent bone integration, and the ability to bond with
the Ti sample. It is thus possible to use Ti-based BMGs in biomedical applications.

Ti-based bulk metallic glasses (BMGs) arepromising materials for applications in biomedical
fields owing to their high corrosion resistance,
excellent mechanical properties, and good
biocompatibility. Many Ti-based BMGs have beendeveloped in the framework of Ti–Ni–Cu and Ti–Zr–
Cu–Ni alloy systems. However, these Ti-based
BMGs contain Ni, Be, etc., which are unsuitable foruse in the human body because of their cellular
toxicity, limiting the application of Ti-based BMGs inbiomedical fields. We developed Ni- and Be-free
Ti–Zr–Cu–Pd BMGs with high strength and good
corrosion resistance, showing that it is possible tocreate novel Ti-based BMG implants [1]. However,
the relatively low glass-forming ability (GFA) (with acritical diameter of 7 mm) of these BMGs restricts
their use in biomedical applications. Large critical
diameters and excellent mechanical properties arefundamental requirements for such BMGs.
We investigated the influence of small amountsof additional elements on the formation andproperties of Ti–Zr–Cu–Pd bulk glassy alloys. Minor
Sn addition improved the glass-forming ability,
thermal stability, and plasticity of the Ti–Zr–Cu–Pd
alloy system [2]. The stress corrosion cracking(SCC) behavior in Hanks’ solution and the bioactivityof Ti–Zr–Cu–Pd–Sn BMGs were also investigated.
The results revealed that the Ti-based BMGs
exhibited low SCC susceptibility in simulated body
fluid. A bioactive calcium phosphate compound
layer was obtained after two-step treatment on the
Ti-based BMGs [3].
We implanted bars of the developed Ti–Zr–Cu–
Pd–Sn BMG in the femoral bones of rats, followed
by investigation of the local tissue reaction, as well
as of local and whole-body component ion diffusion.
After 12 weeks’ implantation, inflammatory reactions,
implant dislocation, or loosening were not observedin any of the cases. In vivo implant evaluation
showed that the Ti-based BMG had good tissuecompatibility, equivalent bone integration, and theability to bond with the Ti sample (Fig. 1). No
component ion diffusion was detected up to 3
months’ post implantation (Fig. 2) [4]. Thus, theFig. 1 Histological views of Ti-based BMG implant and Ti
implant [4]. Both samples are well covered bysurrounding bone tissue. There were no abnormal
findings in the surrounding bone tissue. Objective
magnification of the upper images is ×4 and that of thelower images is ×20.

Fig. 2 EDX elemental analysis of implant border area [4].
No diffusion of any metallic ions in the BMG sample
was found.

feasibility and efficacy of Ti-based BMGs for use asbone implants was confirmed.
References[1] S. L. Zhu, X. M. Wang, F. X. Qin, M. Yoshimura, and A. Inoue,
Mater. Trans. 48, 2445 (2007).
[2] S. L. Zhu, G. Q. Xie, A. Inoue, Z.D. Cui, X. J. Yang, and W.
Zhang, Mater. Sci. Forum 833, 79 (2015).
[3] F. X. Qin, S.L. Zhu, Z. H. Dan, A. Kawashima, and G. Q. Xie, J.
Alloys Compd. 615, S123 (2014).
[4] R. Kokubun, W. Wang, S. L. Zhu, G. Q. Xie, S. Ichinose, S. Itoh,and K. Takakuda, Bio-Med. Mater. Eng. 26, 9 (2015).

Keywords: bulk metallic glass, biological, mechanical properties
Guoqiang Xie (Advanced Materials Development and Integration of Novel Structured Metallic and Inorganic Materials)
E-mail: xiegq@imr.tohoku.ac.jp
URL: http://amdi-pro.imr.tohoku.ac.jp/en/index.html

IMR KINKEN Research Highlights 201615

Infrastructural Materials

Positron–Monovacancy Interaction in d-Block Metals

Dr. Ishibashi is a core member of CMRI and has been conducting numerous studies based on positrons,
which are known as powerful probes for detecting vacancy-type defects in various solids. Combined withtheoretical calculations, it has become possible to identify defect species. The effect of a trapped positron on
the monovacancy structure was systematically investigated. The present results are useful in predicting positronannihilation parameters accurately.

To describe the positron state in solids, Boroński
and Nieminen proposed the two-component densityfunctional-theory formalism [1], with which interactions
between a positron and electrons, as well as between
a positron and nuclei, are explicitly described. In
many practical calculations, a simplification is madeassuming that the positron affects neither theelectronic structure nor the atomic arrangement. This
simplified scheme is called the “conventional
scheme”. The presence of a trapped positron affects
the electronic structure and the atomic arrangement
at a certain level, depending on the material being
investigated. With both conventional and twocomponent DFT schemes, we recently calculated
Doppler-broadening spectra and positron lifetimes
for divacancies in C, Si, Ge, SiC, AlN, GaN, and InN,
and we found that the difference between the two
schemes depends on the bulk modulus [2]. For
relatively soft materials, Si and Ge, the difference issignificant. In the present study, we expanded ourinvestigation to the positron–monovacancy interactionin d-block metals (except for Mn, Tc, and Hg) [3].
All the calculations were performed using our
computational code QMAS (Quantum MAterials
Simulator). In the conventional scheme, electronic
structures, if necessary, and atomic positions arecalculated independently of the presence of apositron. On the other hand, in the two-component
scheme, electronic structures and atomic positions(when they are relaxed) are affected by the presenceof a positron. Calculations were performed onsupercells with sizes of 4 × 4 × 2 for hcp, 3 × 3 × 3 forfcc, and 4 × 4 × 4 for bcc. Further details aredescribed in Ref. [3].
Figure 1 represents the positron density
distribution trapped at a monovacancy in bcc Fe as an
example of the obtained results. Differences between
the positron lifetimes obtained by the two schemes, Δτ,are plotted in Fig. 2 as a function of the atomic number,
Z. For the unrelaxed structure, the positron lifetime
calculated with the presence of a positron is generally
longer than that obtained neglecting the positronFig. 1 Positron density distribution trapped at a monovacancy
in bcc Fe. Two levels of isosurfaces are shown.

Fig. 2 Z-dependence of the differences in positron
lifetimes trapped at a monovacancy, Δτ, calculated withno relaxation (NR) and relaxation (RL).

effect. When the atomic positions are relaxed without
the positron effect, for most cases, inward relaxation of
the atoms surrounding the monovacancy is observed.
However, this relaxation is suppressed when thepositron effect is taken into account. Thus, thedifference in the positron lifetime is widened, especiallyfor the group V metals. As is the case forsemiconductors, these differences are also related tothe bulk modulus and the cohesive energy [3].
References[1] E. Boroński and R. M. Nieminen, Phys. Rev. B 34, 3820 (1986).
[2] S. Ishibashi and A. Uedono, J. Phys.: Conf. Ser. 674, 012020(2016).
[3] S. Ishibashi, J. Phys. Soc. Jpn. 84, 083703 (2015).

Keywords: positron annihilation, first-principles calculations, vacancy
Shoji Ishibashi [Research Center for Computational Design of Advanced Functional Materials (CD-FMat), AIST]
E-mail: shoji.ishibashi@aist.go.jp
Tetsuo Mohri (Project Leader of Computational Materials Research Initiative)
E-mail: tmohri@imr.tohoku.ac.jp

16

IMR KINKEN Research Highlights 2016

Energy-related Materials

IMR KINKEN Research Highlights 2016

Energy-related Materials

Development of Crystal Growth Technology for Producing
High-quality Multicrystalline Si Ingots for Solar Cells

Growth technology for obtaining a high-quality multicrystalline Si (mc-Si) ingot for solar cells is developed on

the basis of the concept that mc-Si ingots grow under non-wetting/non-reacting conditions. The mc-Si ingot
grown under such conditions had a higher minority carrier lifetime than the mc-Si ingot grown using a
conventional method. This technology will be a powerful tool for realizing high-performance solar cells.

In the photovoltaic market, solar cells made ofpolycrystalline Si (commonly expressed as
multicrystalline Si, mc-Si) are the main products
both at present and potentially in the future by totallyconsidering the production cost, storage of raw
materials, safety, reliability, and energy conversion
efficiency of the solar cells. However, in theconventional method for growing mc-Si ingots, it isdifficult to avoid contaminating the mc-Si ingot with
impurities during the melting/solidification process,where impurities in the Si3N4 powder used to coatthe crucible dissolve into the Si melt. Si3N4 powder
can also detach from the crucible and be dissolved
into the Si melt. Such impurities act as a lifetime
killer and a source of dislocations, which degrades
the quality of the mc-Si ingots.
We had an idea that if a mc-Si ingot could begrown under non-wetting and non-reacting
conditions, the problem of impurity contamination
during the growth process would be solved.
Therefore, the growth conditions, including the
crucible material and coating, atmosphere, andthermal history during the melting/growth process
were systematically investigated.
Figure 1 shows the top surfaces of as-grown
mc-Si ingots grown using our method and aconventional method [1]. The difference in theshininess of both ingot surfaces is evident. Although
inclusions of Si3N4 powder are observed on thesurface of the ingot grown using the conventional
method, no such inclusions are observed in theingot grown using our method, which is thus muchshinier. The side and bottom surfaces of both asgrown mc-Si ingots are also shown in Fig. 1. The
surfaces of the ingot grown in our method are verysmooth and shiny, whereas the grain structures are
not visible, while the surfaces of the ingot grown inthe conventional method were rough and the grain
structures were visible. The minority carrier lifetimeof our ingot was much higher than that of theconventionally grown mc-Si ingot. These results
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/

18

IMR KINKEN Research Highlights 2016

Fig. 1 (a) Top surfaces of as-grown mc-Si ingots grownunder (a) a non-wetting and (b) conventional conditions.

indicate that our technology has the potential to bea powerful tool in the near future for the productionof high-quality mc-Si ingots for solar cell applications.
References[1] K. Fujiwara, Y. Horioka, and S. Sakuragi, Energy Science &Engineering 3, 419-422, (2015).

IMR KINKEN Research Highlights 2016

Application of Multi-physics Simulator Based on Molecular
Dynamics Method for Materials DesignN

ext-generation materials design strongly requires a deep understanding of multi-physics phenomena,
including chemical reactions, impacts, fluid, heat, etc. We applied our developed multi-physics computational
simulator based on the molecular dynamics method to the complicated multi-physics phenomena and processes,
contributing to the materials design related to the mechanical engineering such as fuel cells, electronics, etc.
Highly functional and high-performancematerials are necessary in a wide variety of research
fields such as fuel cells, electronics, tribology, etc.
in order to solve energy and environmental problems
and to realize a safe and secure society. Recently, a
deeper understanding of multi-physics phenomena,
including chemical reactions, impacts, fluid, heat,etc. is required for designing material and systemtechnologies. However, traditional simulation
methods such as first-principles calculations andfluid mechanics cannot simulate such multi-physics
phenomena. Therefore, we applied our multiphysics simulator, which was based on tight-binding
molecular dynamics, molecular dynamics, etc., topioneering next-generation materials design [1-2].
In solid oxide fuel cells, which are expected tobe next-generation power generators, the anodematerial, consisting of Ni and ceramic nanoparticles,
needs to exhibit durability during sintering of the Ni
particles. Therefore, we performed a multinanoparticle sintering simulation and investigated thedifferent sintering processes for Ni/YSZ and Ni/ScSZ
nanoparticles. The degree of sintering of the Ni
nanoparticles in the Ni/YSZ model shown in Fig. 1(a)is larger than that in the Ni/ScSZ model shown in Fig.
1(b). This indicates that Ni/ScSZ provides more
durability to sintering. Our multi-nanoparticle sintering
simulator is therefore useful for designing durable,
high-performance anodes [1].
Hydrogenated amorphous silicon carbide(a-Six Cy Hz) is expected to be applicable to electronic
and optical devices. The atomic fractions in theplasma-enhanced chemical vapor deposition (CVD)
process are important in terms of the performance ofthe carbide. Thus, we performed a CVD growthsimulation of a-Six Cy Hz, where CH3 or SiH3 radicals
are irradiated to a Si substrate (Fig. 2). In thesimulation, a surface-adsorbed CH2 species with adangling bond (DB) is generated and then inserted
into a neighboring Si–Si bond, converting it to a Si-C
bond. The bond rearrangement transfers the DB fromthe C to the Si atoms. A CH3 radical is then adsorbed

Fig. 1 Cross-sectional snapshots of time evolution of (a)Ni/YSZ and (b) Ni/ScSZ multi-nanoparticle models.

Fig. 2 Snapshots of CVD simulation with the continuous
impingement of CH3 and SiH3 radicals. (Bottom)
Schematic images corresponding to each configuration.

on the Si atom, forming a Si–C bond. The absence of
DBs on the C atoms supresses the formation of C–C
bonds. We thus found the reason why Si–C bonds
are preferentially formed instead of C–C bonds in the
CVD process [2].
References[1] J. Xu, S. Bai, Y. Higuchi, N. Ozawa, K. Sato, T. Hashida, and M.
Kubo, J. Mater. Chem. A 3, 21518 (2015).
[2] T. Kuwahara, H. Ito, K. Kawaguchi, Y. Higuchi, N. Ozawa, and
M. Kubo, J. Phys. Chem. C 120, 2615 (2016).

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

IMR KINKEN Research Highlights 201619

Energy-related Materials

The Diffusivity and Solubility of Copper in a Reactor
Pressure Vessel Steel Studied by Atom Probe TomographyT

he diffusion coefficient, D, and the solubility limit, c, of copper (Cu) in nuclear reactor pressure vessel (RPV)
steels are important parameters for understanding the Cu precipitation, which causes irradiation-induced
embrittlement of RPV steels. By using atom probe tomography, the values of D and c were directly measured
at lower temperatures close to the real conditions for RPV steels in operation.
Copper (Cu) precipitation plays an importantrole in the irradiation-induced hardening of nuclear
reactor pressure vessel (RPV) steels. Thus, thediffusion coefficient, D, and the solubility limit, c, of
Cu in RPV steels are important parameters forunderstanding the kinetics of precipitation.
The D and c values of Cu in iron (Fe) aremeasured at temperatures higher than ~700 °C
because conventional techniques require long-range
diffusion over distances of at least several micrometers
due to the spatial resolution limit. Therefore, thevalues of D and c at ~300 °C, which is the temperatureof RPVs used in light-water reactors in operation, aregenerally determined by extrapolation from thelimited temperature range, leading to potential
uncertainties. Direct measurements of D and c at
lower temperatures are necessary for accurate
determination, but they have not yet been obtained.
We recently employed atom probe tomography(APT) to observe the very short-range (several tensof nanometers) diffusion of Cu in an Fe matrix [1].
Diffusion couples of Cu–Fe were annealed and thepenetration of Cu into Fe was observed by APT. The
D and c values of Cu in Fe were directly measured
at temperatures from 550 to 750 °C, temperaturesthat are 150 °C lower than temperatures used inprevious studies. In this study, the same method
was applied to study the D and c values of Cu in
A533B steel, a typical RPV steel [2]. A533B waselectropolished and coated with Cu using vapor
deposition, followed by annealing under three
conditions: 550 °C for 1,008,000 s, 600 °C for
250,000 s, and 700 °C for 3,000 s.
Figure 1 shows a typical set of atom maps for Cu
and Fe obtained for the A533B specimen annealed
at 700 °C. The diffusion of Cu into A533B is clearlyobserved. The D and c values were determined byapplying Fick’s second law to the concentration
profiles of Cu assuming a concentration-independent
diffusion coefficient, a semi-infinite medium, and aconstant surface concentration.
Figure 2 shows the Arrhenius plot of D as a

Fig. 1 Atom maps for Cu and Fe for the A533B specimen
annealed at 700 °C for 3,000 s.

Fig. 2 Arrhenius plot for diffusion coefficient of Cu in
A533B steel and that in pure Fe.

function of temperature in A533B steel and in pure
Fe. The obtained dataset was well-fitted using theArrhenius equation, D = D0 exp(−Q/kBT), where D0
is the pre-exponential factor of 89 m2/s and Q is theactivation energy of 3.45 × 105 J/mol. It was foundthat the activation energy for the A533B steel was
higher than that for Fe, Q = 3.11×105 J/mol. It wasalso revealed that the c value in A533B was almost
the same as that in Fe at temperatures ranging from
550 to 700 °C.
References[1] T. Toyama, F. Takahama, A. Kuramoto, H. Takamizawa, Y.
Nozawa, N. Ebisawa, M. Shimodaira, Y. Shimizu, K. Inoue, and
Y. Nagai, Scripta Mater. 83, 5 (2014).
[2] M. Shimodaira, T. Toyama, F. Takahama, N. Ebisawa, Y.
Nozawa, Y. Shimizu, K. Inoue, and Y. Nagai, Mater. Trans. 56,
1513 (2015).

Keywords: atom probe tomography, nuclear materials, diffusion
Yasuyoshi Nagai, Koji Inoue, Yasuo Shimizu, Kazuaki Nagumo (Irradiation Effects in Nuclear and Their Related Materials Division)
E-mail: nagai@imr.tohoku.ac.jp
URL: http://wani.imr.tohoku.ac.jp/

20

IMR KINKEN Research Highlights 2016

IMR KINKEN Research Highlights 2016

Dynamic Observation of Hydrogen Behavior by Particle
Scattering Combined with Optical Measurements

We applied ion beam analysis techniques combined with optical analysis to investigate the hydrogen behavior

in functional materials under an irradiation environment. Simultaneous measurements of hydrogen and lightemission revealed the trapping and release mechanism of hydrogen in connection with the implantationinduced damage in functional materials.
LiTaO 3 <0001>
Normalized yield

D (NRA)Ta (RBS)

Luminescence intensity
Deuterium retention

Angle from <0001>
1.2

isochronal annealing

LiTaO 31.0
0.8

luminescenceintensity

0.6
0.4

deuterium
retention

5keV D
implantation

0.2
0.0
1

2

3

21

4

-2

400

600

800

H fluence (10 m ) Temperature (K)Fig. 1 Luminescence intensity and D retention in the
LiTaLo3 crystal during ion implantation and thesubsequent heat treatment. The angular scan yields
along the <0001> axis are inserted in the upper part.
1.5

Luminescence intensity
H and O concentration

Ion beam analysis (IBA) techniques are powerful
and unique tools used to determine the atomic
concentration as a function of depth to several microns.
The fast and non-destructive characteristics of IBA
allow in-situ observation of time-dependent phenomena
in functional materials [1]. For example, the investigationof compositional changes in a thin film during theanodizing process gives us a better understanding of
the formation mechanism of the corrosion-resistantsurface [2]. IBA is also useful for examining hydrogentransport behavior in energy production and storage,such as in electrolytes for batteries and fuel cells [3],solid breeders for fusion reactors, and polymer films forradiation measurements [4].
Li-based oxides are regarded as candidates foruse as breeder materials for multiplying hydrogenisotopes as the fuel in fusion. Since hydrogen interacts
strongly with defects, it is able to know the hydrogen
behavior by examining optical characteristics that are
sensitive to defects in oxides. The luminescence from
LiTaO3 decreased with increasing incident D ion
fluence, as shown in Fig. 1. After stopping theimplantation, the subsequent heat treatment showed
recovery of the luminescence intensity with increasing
release of D atoms from the implanted depth, indicating
implantation-induced defect trapping of D atoms.
According to the ion channeling along the <0001>
and <11-20> axes directions, D atoms are considered
to be located preferably at the substitutional sites of
the Li sublattice in the LiTiO3 crystal.
Luminescent materials are attractive for making
scintillators for radiation detection. Polyethylene
naphthalate (PEN), consisting of two benzene rings,
exhibits strong blue luminescence in response toirradiation. Generally, the optical properties of organic
materials are altered effectively and permanently byionizing radiation. In the case of the PEN film, air
exposure caused the recovery of luminescence,accompanied by the immediate accumulation of H
atoms in the ion-implanted region, whereas the O
concentration did not change, as shown in Fig. 2.

air exposure

Polyethylene
naphthalate
1.0

Oxygen0.5

Hydrogenluminescence

0.0

0

5

10

H ion fluence (10

18

15

-2

20

m )

Fig. 2 H and O concentrations and the luminescenceintensity in the surface layer of the PEN film during the 1
MeV H implantation and air exposure.

References[1] S. Nagata, H. Katsui, K. Hoshi, B. Tsuchiya, K. Toh, M. Zhao, T.
Shikama, and E.R. Hodgson, J. Nucl. Mater. 442, 501 (2013).
[2] K. Shahzad, E. Tsuji, Y. Aoki, S. Nagata, and H. Habazaki,
Electrochim. Acta 151, 363 (2015)[3] B. Tsuchiya, K. Morita, S. Nagata, T. Kato, Y. Iriyama, H. Tsuchida,
and T. Majima, Surf. Interf. Anal. 46, 1187 (2014)[4] S. Nagata, M. Mitsuzuka, S. Onodera, T. Yaegashi, K. Hoshi,M. Zhao,
and T. Shikama, Nucl. Instr. Meth. Phys. Res. B 315, 157 (2013).

Keywords: ion beam analysis, luminescence, hydrogen implantation
Shinji Nagata (Nuclear Materials Science Division)
E-mail: nagata@imr.tohoku.ac.jp
URL: http://www-lab.imr.tohoku.ac.jp/~wshikama/

IMR KINKEN Research Highlights 201621

Energy-related Materials

Modeling of One-dimensional Migration of Self-interstitial
Atom Clusters in Steels for Nuclear Materials

We propose a new mechanism for one-dimensional (1D) migration of self-interstitial atom (SIA) clusters inconcentrated alloys induced by high-energy particle irradiation. The model explains in-situ observation of 1D
migration in various steels used for nuclear power plants under electron irradiation using high-voltage electron
microscopy.

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

22

IMR KINKEN Research Highlights 2016

0

5

10

(nm)
15

20

25

30
0

0.0

1.0

5

30%Cu

10%Cu

3%Cu

Fe-1%Cutime (ns)

0.5

10

1.5

15

2.0

20

exchange per atom(a)

10 epa ns-1

formation energy of I-cluster

Recent theoretical and experimental studies
have confirmed that small interstitial atom (SIA)
clusters in pure metals make a gliding motion along
the direction of the Burgers vector with low activationenergies, called one-dimensional (1D) migration.
This phenomenon has been suggested to affectdefect structural development under irradiation withhigh-energy particles, such as void swelling.
Although 1D migration processes in practical alloys
have technical and fundamental significance fordeveloping materials for nuclear power applications,they are not well understood.
We propose a mechanism for 1D migration inconcentrated alloys driven by high-energy particle
irradiation, called “radiation-induced glide motion”[1]. SIA clusters are fundamentally mobile on theirrespective 1D migration tracks, but in concentrated
random alloys they are stationary at the position
where the fluctuating formation energy achieves a
local minimum. Irradiation successively alters the
microscopic distribution of solute atoms from one
random distribution to another through atomic
displacements and the subsequent recovery of the
produced point defects. The interatomic mixing
changes the stable cluster position on the track andcauses the clusters’ 1D migration into a new stable
position. Moreover, growth and shrinkage ofinterstitial clusters under irradiation changes the
microscopic distribution of solute atoms around theloop dislocation itself, which results in another 1D
migration.
Molecular dynamics simulations revealed theoccurrence of stepwise 1D migration in Fe–Cu
alloys under exchanges of atoms or cluster
shrinkage: a single 1D migration was induced on
average by two exchanges per atom or a cluster
radius change by two interatomic distances. The 1D
migration distance ranged up to several nanometers.
The model explained experimental 1D migration invarious alloys under in-situ observation using highvoltage electron microscopy [2]. The short-range 1D
migration (<10 nm) of SIA clusters reflects the
wavelength of the fluctuation of the formation energy

1.4 ns (b)n= (339)
1.5 ns(339)

2 eV

1.6 ns(177)
1.7 ns(177)
1.8 ns(177)
1.9 ns
(186)

0

20
40
60
80
100
center of mass of I-cluster (b)120Fig. 1 (a) Results of molecular dynamics simulation on
trajectory of center of mass of SIA clusters (217i) under
random exchanges of first-nearest pair of atoms in Fe–
Cu alloys. (b) Variation of the formation energy profileand the plane of the interstitial cluster in Fe–10%Cu [1].

of SIA clusters, which gives the characteristic lengthof 1D migration in concentrated alloys.
References[1] Y. Satoh, H. Abe, and T. Matsunaga, Philos. Mag. 94, 2170
(2014).
[2] Y. Satoh, H. Abe, Y. Matsukawa, T. Matsunaga, S. Kano, S.
Arai, Y. Yamamoto, and N. Tanaka, Philos. Mag. 95, 1587
(2015).

IMR KINKEN Research Highlights 2016

Three-dimensional Bicontinuous Porous Carbon Generated in LowTemperature Metallic LiquidAthree-dimensional bicontinuous porous carbon (3Dbp-carbon) with a well-developed graphite structure was generated bydealloying in a metallic melt at low temperatures. Both X-ray diffraction and the Raman spectra indicated that 3Dbp-carbon
became more ordered after the graphitization process. However, the surface area and total pore volume did not significantly
decrease, indicating that porous graphite with extremely high electron conductivity and durability can be obtained by optimizing
the dealloying and the subsequent activation processes.
Carbon black (CB) is commonly used for electrodematerials because of its several advantages. Nevertheless,
CB has problems such as high electrical resistivity and low
durability owing to its low crystallinity. Graphitization is one of
the most effective methods of increasing the graphite ratio ofcarbon-based materials, but it also decreases the surface
area and pore volume of carbon-based materials such as CB,
such that the micropores mostly disappear because ofthermal instability. If porous carbon consisting of meso- andmacro pores can be generated, the surface area and porevolume originating from these pores should remain after
graphitization because of its high thermal stability. To
synthesize these new carbon materials, we previously
developed a dealloying process in a metallic melt [1, 2], asimple top-down process for fabricating three-dimensionalbicontinuous porous carbon.
In the current study, we synthesized 3Dbp-carbon by
immersing a precursor of Mn85C15 (at%) in a pure Bi melt at
1073 K. Because Mn is miscible with Bi but carbon is not, only
Mn atoms dissolved in the Bi melt, and the unstable carbon
atoms spontaneously organized into a nanoporous structure.
Fig. 1(a) and 1(b) show SEM images of the products.
Two types of porous materials with different porosities were
found. When the Mn85C15 precursor, consisting of α-Mn and
Mn23C6, was dipped into the Bi melt, α-Mn first reacted with
the Bi melt to selectively dissolve Mn atoms; the remaining
carbon atoms then diffused on the boundary between the
precursor and the Bi melt, resulting in self-organized 3Dbpcarbon with a relatively high porosity (Fig. 1(a)). Then, Mn23C6,
facing the penetrated Bi melt, slowly reacted with the Bi melt,
resulting in 3Dbp-carbon with relatively low porosity (Fig. 1(b))
by boundary diffusion.
The XRD patterns shown in Fig. 2(a) indicate that 3Dbpcarbon became more ordered with increasing graphitization

Fig. 1 SEM images of the original (a) α-Mn and (b) Mn23C6 structuresof 3D bicontinuous porous carbon prepared by immersing aprecursor of Mn85C15 (at%) in a pure Bi melt at 1073 K.

Fig. 2 Comparison of the (a) XRD patterns and (b) Raman spectra
before and after graphitization at different temperatures for 2 h.

temperature. The full width at half maximum (FWHM) andlattice spacing for the (002) plane (d002) decreased withincreasing graphitization temperature. FWHMG and theintensity ratio of the D band to the G band decreased withincreasing graphitization temperature, as shown in Fig. 2(b).
The surface area of 3Dbp-carbon moderately decreased
graphitization at 2773 K. Nevertheless, the total pore volume
was almost the same value (~0.8 cm3/g) as that under othergraphitization conditions. This indicates that the porous
structure of the graphitic carbon generated by this dealloying
technique is stable during high-temperature graphitization.
References[1] SG. Yu, K. Yubuta, T. Wada, and H. Kato, Carbon 96, 403 (2016).
[2] T. Wada, K. Yubuta, A. Inoue, and H. Kato, Mater. Lett. 65, 1076 (2011).

Keywords: foam, porosity, energy storage
Hidemi Kato (Non-Equilibrium Materials Division)
E-mail: hikato@imr.tohoku.ac.jp
URL: http://www.nem.imr.tohoku.ac.jp/

IMR KINKEN Research Highlights 201623

Energy-related Materials

Strategy for Obtaining Further Hydrogen-rich Materials

T

he recent discovery of the highest superconductivity in the sulfur hydride system has stimulated rapidly
growing interest in exploring hydrogen-rich materials. Here, we present a strategy for obtaining novel complex
transition-metal hydrides containing high-H-coordination hydride complexes.
Hydrogen, in spite of being the simplest
element, exhibits an exceptionally rich chemistry,
forming various types of chemical bonds inmaterials. This chemical flexibility is the source ofmany interesting properties of hydrides, such ashydrogen storage, fast ionic conductivity,
magnetism, and metal–insulator transitions [1].
Especially, the recent discovery of superconductivity
at 203 K in the sulfur hydride system [2] has spurred
research in terms of the exploration of hydrogen-richmaterials.
Complex transition-metal hydrides are a typicalclass of hydrogen-rich materials. In these hydrides,
a number of H atoms covalently bond to transition
metals to form a varied set of homoleptic transitionmetal hydride complexes with a remarkably richvariety of H coordination modes. At the same time,
despite research spanning the past several
decades, the presently known transition metals
capable of forming such complexes are limited toGroups 7–12.
By means of a combined theoretical andexperimental approach, we recently demonstrated
the formation of the first Group 6 hydride complex[CrH7]5– in Mg3CrH8 [3]. Our density functional
theory (DFT) calculations predict that pentagonalbipyramidal ligand-field allows the formation ofstrong σ-bonds between H and Cr, thus stabilizing
the hydride complex with seven-fold H coordination.
The prediction is strongly supported by neutron
diffraction (Fig. 1) and infrared (IR) spectroscopic
measurements.
In general, the H coordination number increases
when going from right to left along a period primarily
because of the increase in atomic size, which allows
more H atoms to bond (Fig. 2). Thus, our findings
strongly suggest high potential for further discovery
of hydride complexes with higher H coordination of
the unexplored Group 3–6 elements.

Fig. 2 Schematic of strategy for obtaining hydridecomplexes with high H coordination.

References[1] S. Takagi and S. Orimo, Scripta Mater. (Viewpoint paper) 109,
1 (2015).
[2] A. P. Drozdov, M. I. Eremets, I. A. Troyan, V. Ksenofontov, andS. I. Shylin, Nature 525, 73 (2015).
[3] S. Takagi, Y. Iijima, T. Sato, H. Saitoh, K. Ikeda, T. Otomo, K.
Miwa, T. Ikeshoji, K. Aoki, and S. Orimo, Angew. Chem. Int. Ed.

Fig. 1 Neutron diffraction profiles of Mg3CrH8. Simulated
profile from DFT structure (top) and experimental profile(bottom).

54, 5650 (2015).

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

24

IMR KINKEN Research Highlights 2016

Electronic Materials

IMR KINKEN Research Highlights 2016

Electronic Materials

Antiferromagnetic Skyrmions

Topological spin textures such as skyrmions have been actively studied in ferromagnets over the past several

years as they may become bits of information in future spintronic memory devices. We propose to study similar
topological objects in antiferromagnets, in which the topology and the presence of two sublattices have a large
effect on the dynamical and thermal properties.

Manipulating spin textures by electric and spincurrents is one of the main challenges in the field of
spintronics. Ferromagnetic skyrmions are attracting
a lot of attention because they are small and notpinned as easily as domain walls when driven byelectric currents. However, ferromagnetic skyrmions
have disadvantages as well, such as the presenceof stray fields and transverse motion, making it moredifficult to employ them in spintronic devices. In thiswork, we propose a novel topological object,
antiferromagnetic (AFM) skyrmion, and we explore
its properties analytically and by micromagnetic
simulations. This topological texture has no strayfields, as shown in Figs. 1(a) and (b), and it is moremobile than its ferromagnetic analogue.
We found that the Dzyaloshinskii–Moriya
interaction, which comes from relativistic spin-orbit
effects and generally favors spin spiral structures,stabilizes the AFM skyrmions. The AFM skyrmion
radius dependes on the strength of the
Dzyaloshinskii–Moriya interaction and temperature.
Moreover, the thermal properties, such as the radiusand diffusion constant, differ from those offerromagnetic skyrmions. Because of the unusual
topology, the AFM skyrmions do not experience atransverse (Magnus) force and therefore do not
move transverse to an applied current [Fig. 1(c)],which makes them interesting candidates for
spintronic applications [1]. These results can beunderstood in terms of a generalized Thiele
equation, which describes soft modes of theskyrmion motion. This equation shows an exact
cancelation of the Magnus force due to the presenceof two AFM sublattices with opposite topologicalcharges. It also leads to a larger diffusion constantof the AFM skyrmion as compared to its
ferromagnetic counterpart.
The next step will be to investigate the efficiencyof temperature gradients for the propagation ofskyrmions in antiferromagnetic insulators and todevelop a theory of spin-orbit torque driven AFM
skyrmion motion in AFM/heavy metal bilayers.

c

IMR KINKEN Research Highlights 2016

spin current js-1
drag force

Magnus force

Fig. 1 (a)–(b) The spin texture of an antiferromagnetic(AFM) skyrmion: (a) top view of the AFM skyrmion and(b) skyrmion’s cross section. (c) The AFM skyrmion is acomposite topological object consisting of a skyrmion
on one sublattice and an antiskyrmion on the other. This
results in the cancelation of the overall Magnus force
and therefore the absence of the topological Hall effect.

References[1] J. Barker and O. A. Tretiakov, Phys. Rev. Lett. 116, 147203(2016)

Keywords: skyrmions, Dzyaloshinskii-Moriya interaction, antiferromagnets
Oleg Tretiakov (Theory of Solid State Physics Division)
E-mail: olegt@imr.tohoku.ac.jp
URL: http://www.bauer-lab.imr.tohoku.ac.jp/index_e.html

26+1IMR KINKEN Research Highlights 2016

Fusion of Pulse Fields and Pulse X-ray Unveils New Charge
Density Wave State

Development of a three-dimensional correlation of a charge density wave in YBa Cu O

2
3 6.67 was discovered bysingle-shot X-ray diffraction in high magnetic fields. The combination of the pulsed magnet and the intense
pulse X-ray enabled us to pick up the extremely weak super-lattice modulation caused by the magnetic fieldinduced electronic phase transition.

High magnetic fields induce various electronic
phase transitions such as metal–insulator, charge
density wave (CDW), and valence-state transitions.
Unique structural anomalies are associated withthese transitions, but observations of such tinychanges of crystal symmetry and/or volume havebeen difficult. For example, CDW states appearing
under high magnetic fields in Cu oxide
superconductors have been intensively studied.
However, direct observation of a CDW super-lattice
peak has been made only in magnetic fields much
lower than the upper critical fields. An ultimate tool toinvestigate such small lattice modulations in extremely
high magnetic fields had been sought for long time.
In the current study, we combined two pulsed
tools, a pulsed magnet and a pulsed X-ray source, toaccomplish this difficult task. The magnetism divisionof IMR has developed an extremely compact splitpair magnet generating magnetic fields of over 30 T.
The bore of the coil is only 3 mm and the length of thecoil is as short as 25 mm. The SLAC National
Accelerator Laboratory offers the most intense pulsed
laser source on earth. When these two tools are
combined, weak CDW peaks in YBa2Cu3O6.67 canbe detected clearly in a single-shot pulsed magnetic
field [1]. It should be also noted that IMR offers acompact capacitor bank developed and assembled
at the magnetism division. The “flying magnet” andthe “rolling capacitor bank” make this fusion possible.
In the present experiments, a new CDW state withstrong three-dimensional correlation was discovered.
The index of this CDW state is given by (δ, 0, l), whereδ is related to the localized charge modulation in thec-plane. Moreover, the index l was found to be an
integer. This unique feature is in sharp contrast to thetwo-dimensional CDW peak found in lower magnetic
fields at the (δ, 0, l/2) position, where the modulation
pitch along the c-axis is doubled. The intensity of the l= integer peak increased rapidly in high magnetic
fields, whereas that of the half-integer peak saturated
in lower magnetic fields. The appearance of a statewith localized electrons with such strong three-

The figure shows the X-ray diffraction chamber used at
Linac Coherent Light Source at SLAC National
Accelerator Laboratory for a single-shot high-magneticfield X-ray diffraction and the split-pair pulse coil
mounted on the cold finger of the specimen.

dimensionality shows the essential role of the strong
electron correlation in the normal state of YBa2Cu3O6.67
and the existence of a few competing interactions. The
present experiment demonstrates the power of the
new tool for investigating magnetic field-induced
electronic transitions.
References[1] S. Gerber, H. Jang, H. Nojiri, S. Matsuzawa, H. Yasumura, D. A.
Bonn, R. Liang, W. N. Hardy, Z. Islam, A. Mehta, S. Song, M.
Sikorski, D. Stefanescu, Y. Feng, S. A. Kivelson, T. P. Devereaux,Z.-X. Shen, C.-C. Kao, W.-S. Lee, D. Zhu, and J.-S. Lee, Science
350, 949 (2015).

Keywords: high magnetic field, superconducting, 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 201627

Electronic Materials

Fluid-mechanical Spin-current Generation

F

undamental studies of spintronics focus on the manipulation and generation of spin currents. To generate
spin currents, recent studies have utilized several interactions with electron spins in condensed matter; the key
is angular momentum conversion. Here, we experimentally show that fluid-mechanical angular momentum
enables us to generate spin currents.

(a)Spin current
Liquid flow
Flow velocity
Vorticity
Flow velocity

IMR KINKEN Research Highlights 2016

ISH voltage(b)50

Hg flow
2.7 m/s

V

0
V

-50
0

6
Time (s)Fig. 1 (a) Concept of fluid-mechanical spin- current
generation. Translational motion with different velocities
in a local flow region exhibits local rotational motion
whose angular velocity is proportional to the vorticity.
The vorticity gradient becomes a spin-current source.
(b) Time evolution of voltage signals induced by the Hg
flow. The flow was started at 0 s and switched off at 6 s.
The length and inner diameter of the pipe were 80 mm
and 0.4 mm, respectively. The measurements were
performed at room temperature.

References[1] R. Takahashi, M. Matsuo, M. Ono, K. Harii, H. Chudo, S.
Okayasu, J. Ieda, S. Takahashi, S. Maekawa, and E. Saitoh,
Nature Phys. 12, 52 (2016).

Keywords: spintronics, electronic material, spin current
Ryo Takahashi and Eiji Saitoh (Surface and Interface Research Division)
E-mail: takahashi.ryo@jaea.go.jp; eiji@imr.tohoku.ac.jp
URL: http://saitoh.imr.tohoku.ac.jp/

28

Vorticity

Voltage

Voltage (nV)

Macroscopic mechanical rotation is the mostcommon carrier of angular momentum. Mechanicalrotation can interact with electron spins directly, as
suggested by the Barnett effect, inducing spinpolarization by mechanical rotation of a material
object. However, generation of a spin current as aresult of mechanical rotation has not been observed
so far because it requires a mechanical rotation
gradient, and producing such a rotation gradient isdifficult in a solid. However, in fluid motion, and evenin a conventional liquid flow in a pipe, we can easily
generate mechanical rotation by using the vorticity,which is the local rotation of a liquid due to theviscosity near the inner wall [Fig. 1(a)]. Hence, as
the liquid flows through the pipe, a spin current due
to macroscopic motion is expected to be generated
along the direction of the vorticity gradient,perpendicular to the pipe flow.
In the present study [1], to detect the spincurrent in a liquid, especially liquid metals (such as
Hg and the gallium alloy Ga62In25Sn13), we used theinverse spin Hall (ISH) effect, converting a spincurrent into electric voltage perpendicular to thespin-current direction through the spin-orbit
interaction of electrons. Hence, in the pipe flow, theISH voltage is expected to be generated along theflow direction [Fig. 1(a)]. Figure 1(b) shows theresults of measurements of the voltage along theflow direction in the Hg pipe flow. A clear voltage
signal appears when Hg is flowing. The sign of thesignal is reversed upon reversing the flow direction;
this unconventional voltage behavior is predicted forthe ISH effect induced by the mechanical motion
described above. We also examined the consistencyof the current results with the theory on spin-current
generation due to fluid motion [1].
This phenomenon is fundamentally new; itbridges the gap between spintronics andhydrodynamics, and it is expected to become a
stepping-stone to expanding spintronic phenomena
into fluids.

IMR KINKEN Research Highlights 2016

High-Tc Superconductivity of FeSe Emerges in Thinning MannerT

wo-dimensional layered materials possess significant potential to exhibit intriguing physical properties bycombining external electric fields. Iron selenide (FeSe) is a layered material that has received much attention
because of its high superconducting transition temperature (high-Tc) when an atomic monolayer is deposited onto
SrTiO3. Here, we highlight a new approach to obtaining high-Tc superconductivity of ultrathin FeSe films by anelectrochemical reaction in an electric double-layer transistor (EDLT). The EDLT allows layer-by-layerelectrochemical etching of FeSe films down to an atomic monolayer and electrostatic control of the superconductivity.

106
Superconductor to insulartor
transition by discharging

105
104
Rs (Ω)

FeSe is an iron-based superconductor with asuperconducting transition temperature (Tc) of 8 K inbulk form [1]. Stacking of Se–Fe–Se atoms forms alayered crystal structure. The recent astonishingdiscovery of its high-Tc superconductivity with a large
gap of approximately 20 meV corresponding to Tc =65 K has sparked an explosion of investigations ofatomic monolayers of FeSe deposited onto SrTiO3
substrates by mainly in-situ characterization using
photo-emission
andscanning
tunneling
spectroscopies [2, 3]. However, the systematic
thickness dependence of electrical measurements ofthe superconductivity and its electric field effect havenot been addressed so far, mainly because of theexperimental difficulty in obtaining ex-situ
measurements for atomically thin films.
To overcome this issue, we applied the electric
double-layer transistor (EDLT) technique with thick
FeSe films grown by pulsed-laser deposition [4].
EDLTs were originally employed to investigate novel
physical phenomena with significant charge carrier
accumulation. Our team applied the EDLT techniqueto regulate the FeSe film thickness by anelectrochemical reaction, enabling layer-by-layer
etching down to an atomic monolayer. Withdecreasing thickness, a high-Tc superconductivityof 40 K surprisingly emerged in ex-situ electricalresistivity measurements (brown curve in Fig. 1). In
addition, the systematic thickness dependence ofthe superconductivity was successfully revealed inour study. Moreover, electrical control of thesuperconductor-to-insulator transition was realized
via control of the external electric field (from the redto the purple curves in Fig. 1). Our results point out
the importance of electric-field-induced electronic
band
modulationforgenerating
high-Tc
superconductivity in FeSe.
This electrochemical etching approach could
be applied to other layered materials. We believe
this method is a powerful technique for exploringnovel physical phenomena in two-dimensional
layered systems.

103
102
101
100
0

20

40

60
T (K)

80

100

Fig. 1 Superconducting transition behavior in EDLT device
upon applying an external electric field (brown curve).
A decrease in the number of charge carriers(discharging) induced superconductor-to-insulatortransition (from red to purple). (Inset) Schematic imageof atomic layer of FeSe in ionic liquid.

References[1] F. C. Hsu, J. Y. Luo, K. W. Yeh, T. K. Chen, T. W. Huang, P. M. Wu,
Y. C. Lee, Y. L. Huang, Y. Y. Chu, D. C. Yan, and M. K. Wu, Proc.
Natl. Acad. Sci. USA 105, 14262 (2008).
[2] Q. Y. Wang, Z. Li, W. H. Zhang, Z. C. Zhang, J. S. Zhang, W. Li,
H. Ding, Y. B. Ou, P. Deng, K. Chang, J. Wen, C. L. Song, K. He,
J. F. Jia, S. H. Ji, Y. Y. Wang, L. L. Wang, X. Chen, X. C. Ma, andQ. K. Xue, Chin. Phys. Lett. 29, 037402 (2012).
[3] S. He, J. He, W. Zhang, L. Zhao, D. Liu, X. Liu, D. Mou, Y. B. Ou,
Q. Y. Wang, Z. Li, L. Wang, Y. Peng, Y. Liu, C. Chen, L. Yu, G. Liu,
X. Dong, J. Zhang, C. Chen, Z. Xu, X. Chen, X. Ma, Q. Xue, and X.
J. Zhou, Nature Mater. 12, 605 (2013).
[4] J. Shiogai, Y. Ito, T. Mitsuhashi, T. Nojima, and A. Tsukazaki,
Nature Phys. 12, 42 (2016).

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

IMR KINKEN Research Highlights 201629

Electronic Materials

Charge Degrees of Freedom under High Pressure in the
Organic Dimer-Mott Insulator β′-(BEDT-TTF)2ICl2

L

ow-dimensional layered organic conductors are a promising class of materials that exhibit high-temperature
superconductivity. Among them, an antiferromagnetic dimer-Mott insulator, β′-(BEDT-TTF)2ICl2, showedsuperconductivity at 14.2 K under 8 GPa. We performed optical conductivity measurements for β′-(BEDTTTF)2ICl2 under high pressure, which revealed that charge fluctuations inside dimers play an important role inhigh-temperature superconductivity.
The organic conductor β′-(BEDT-TTF)2ICl2,
which shows superconductivity at 14.2 K under highpressure (~8 GPa), has aroused significant interest
because its transition temperature is the highest
among organic superconductors known to date. At
ambient pressure, β′-(BEDT-TTF)2ICl2 is a dimerMott (DM) insulator with an antiferromagnetictransition temperature, TN , of 22 K. As typically seen
in bandwidth-controlled Mott transition systems, β′(BEDT-TTF)2ICl2 also exhibits superconductivity
when the antiferromagnetic phase is suppressed byapplying pressure. It is believed, therefore, that
antiferromagnetic spin fluctuations play an essential
role in high-Tc superconductivity.
To elucidate the effect of pressure on the
superconductivity of β′-(BEDT-TTF)2ICl2, we
measured the polarized infrared (IR) optical spectra
under high pressure using a diamond anvil cell(DAC) [Fig. 1(a)] [1]. At ambient pressure, twocharacteristic bands due to intra- and interdimer
charge transfers were observed in the IR spectra,
indicating that this salt is a typical half-filled DM
insulator at ambient pressure [Fig. 1(b)]. With
increasing pressure, however, the intradimer chargetransfer excitation shifted to much lower energies,
indicating that the effective electronic state changes
from half-filled to three-quarters-filled as a result of
weakening of dimerization [Fig. 1(c)]. This implies
that the system approaches a charge-ordered state
under high pressure, in which charge degrees of
freedom emerge as an important factor. The present
results suggest that in addition to antiferromagnetic
spin fluctuations, charge fluctuations inside dimers
play an important role in high-temperature
superconductivity.
References[1] K. Hashimoto, R. Kobayashi, H. Okamura, H. Taniguchi, Y.
Ikemoto, T. Moriwaki, S. Iguchi, M. Naka, S. Ishihara, and T.

(a)

(c)
Excitation energy
V

Edimer

V

dimer

t

td

3/4-filled Bandw
idthn
CO Metal
tio D
a
z
M
i
β’
r
e
κ
Dim
1/2-filled(b)Fig. 1 (a) Experimental setup for the optical measurements
under high pressure using a DAC. (b) Opticalconductivity spectra of β′-(BEDT-TTF)2ICl2 measured in
the DAC at various pressures. The gray lines in theupper left panel show the σ1(ω) spectra measured atambient pressure. (c) The schematic phase diagram
expected in the extended Hubbard model with themolecular dimer degree of freedom is shown asfunctions of degree of dimerization and bandwidth. The
excitation energies of the Hubbard and dimer bands
are also shown as functions of degree of dimerization.
In β′-(BEDT-TTF)2ICl2, when the pressure is applied,
the system would follow the track drawn by the arrow.

Keywords: organic, superconducting, optical properties
Kenichiro Hashimoto (Low Temperature Condensed State Physics Division)
E-mail: hashimoto@imr.tohoku.ac.jp
URL: http://cond-phys.imr.tohoku.ac.jp/index.html

IMR KINKEN Research Highlights 2016

V

U

EHub

Sasaki, Phys. Rev. B 92, 085149 (2015).

30

2td

IMR KINKEN Research Highlights 2016

Spin Fluctuations on a Triangular LatticeIn geometrically frustrated magnets, spin liquid states attract considerable interest. We quantitatively examined
temporal magnetic correlations of the triangular lattice antiferromagnet NiGa2S4 through thirteen decades(10 -13 –1 s) and elucidated that megahertz spin fluctuations last over an extended temperature regime.
Two-dimensional triangular lattices play a
prominent role in the field of frustrated magnetism.
Although it now seems clear that a conventional
triangular lattice antiferromagnet has a long-range
120-deg order, irrespective of the spin quantum
number, S, experiments on materials withgeneralized longer-range and spin-orbit interactions,as well as lattice distortions, point to a rich variety ofphases in the vicinity of the ordered phase. In thequantum limit (S = 1/2) first considered by Anderson,
experiments on organic materials suggested that agapless spin liquid with a spinon Fermi surface may
exist near the metal–insulator transition.
For larger spin quantum numbers, theoreticaland experimental works have pointed to complex
slow spin dynamics that are still poorly understood.
Here, we focus on such dynamics in the S = 1
triangular lattice antiferromagnet NiGa2S4, which isdistinguished by a two-dimensional incommensurate
magnetic wave vector and the potential for spinnematic interactions.
NiGa2S4 consists of neutral insulating layers
held together by van der Waals forces [inset to Fig.
1(a)]. This curtails electron hopping between layers
and leads to a strongly two-dimensional magnet.
Within each layer, nickel ions with S = 1 reside on an
equilateral triangular lattice. Upholding expectationsof anomalous magnetism, the material does notexhibit conventional magnetic ordering down to atemperature T of 50 mK, and the in-plane correlation
length gradually increases upon cooling but tends
to remain at approximately 2.6 nm (7 latticespacings) without a thermal anomaly [Fig. 1(a)].
In sharp contrast, temporal correlations featureclear thermal anomalies. Figure 1(b) shows thetemperature dependence of the characteristic spin
relaxation time in NiGa2S4. Using high-energy
resolution inelastic neutron scattering, neutron spin
echo, muon spin relaxation, and AC magnetometry,
we provide evidence for emergent MHz spin
dynamics over a wide range of temperatures [1]. Weargue that such slow spin dynamics are associatedwith emergent topologically protected degrees of
freedom inherent to incommensurate magnetism on

Fig. 1 Temperature dependence of (a) the spin correlation
length and (b) characteristic spin relaxation time of
NiGa2S4. The crystal structure of NiGa2S4 is depicted in
the inset to (a). Above and below T*= 8.5 K, the muon
spin relaxation rates are in the motionally narrowed andadiabatic limits, respectively. Vogel–Fulcher behavior
from the AC susceptibility measurements is given by
the dotted curve. The dashed curve in (a) and the solid
curve towards T* in (b) are visual guides.

the triangular lattice.
References[1] Y. Nambu, J.S. Gardner, D.E. MacLaughlin, C. Stock, H. Endo,
S. Jonas, T.J. Sato, S. Nakatsuji, and C. Broholm Phys. Rev.
Lett. 115, 127202 (2015).

Keywords: neutron scattering, triangular antiferromagnet, spin fluctuation
Yusuke Nambu (Metal Physics with Quantum Beam Spectroscopy Division)
E-mail: nambu@imr.tohoku.ac.jp
URL: http://qblab.imr.tohoku.ac.jp/

IMR KINKEN Research Highlights 201631

Electronic Materials

Dislocation-based Plasticity of SiT

he classical idea that semiconductor silicon (Si) is brittle and cannot be deformed plastically at room
temperature (RT) is now changing drastically. Recent experimental findings on the plasticity of Si from RT to its
melting temperature (TM) in terms of dislocation mobility and atomic core structure are reviewed.
Si is a key material in nano-sized devices forultra-large-scale integrated (ULSI) circuits and for
precision instruments for micro-electromechanicalsystems (MEMS). Knowledge of the elastic–plastic
characteristics of Si is essential for controlling its
crystallinity during various fabrication processes. Si
is known to be typically ductile at temperatureshigher than approximately 2/3TM, behavior that isgoverned by dislocation dynamics, whereas atlower temperatures, Si is brittle and susceptible tofracture without plastic deformation owing to theextremely low mobility of dislocations. Thus, there isa ductile-to-brittle transition (TBDT) in the deformation
mode at approximately 600–700°C.
Figure 1 shows the mechanical strength of Si
crystals plotted against the reciprocal temperaturefrom RT to 1300°C [1]. There are two regions withremarkable knees at approximately 400°C, showing
a drastic change in the temperature dependence ofthe strength. At temperatures higher than the knees,
Si deformed by compression or tension underatmospheric pressure, being ductile in conventional
viewpoints. Surprisingly, Si deforms plastically evenat temperatures from RT to the knee under speciallyarranged conditions. Small, thin plates (membranes)or micro-scale pillars whose thickness and diameter,
respectively, are on the order of micrometers, canbe deformed by compression or tension at
atmospheric pressure. Bulk specimens can becompressively deformed without fracture under aconfining (hydrostatic) pressure. Under these
conditions, TBDT decreases to temperatures close to
RT. In low-temperature regions, the yield strength of
Si is as high as 1.5 GPa, almost independent of thetemperature, which is extremely different from its
behavior at high temperatures. This feature leads tothe so-called shuffle–glide controversy on the core
structure of dislocations governing the plasticity of
Si in the relevant temperature regions.
Plastic deformation of a crystal takes placethrough the generation, motion, and multiplication of
dislocations in the crystal under stress. The
processes are controlled by the dynamic propertiesof the dislocations. The dislocation velocity has
Keywords: defects, deformation, semiconducting
Ichiro Yonenaga (Physics of Crystal Defects Division)
E-mail: yonenaga@imr.tohoku.ac.jp
URL: http://lab-defects.imr.tohoku.ac.jp/

32

IMR KINKEN Research Highlights 2016

Fig. 1 Temperature dependence of strength of Si undervarious conditions [1]. DF: dislocation-free, D: dislocated,
PS: pre-strained, CP: under confining pressure.

been well determined experimentally as a functionof stress and temperature.
At high temperatures, the deformation
processes are governed by the dynamic collective
motion of glide-set dislocations. The process canbe reproduced by the constitutive model with mutualinteraction and self-multiplication of dislocations [2].
On the other hand, the generation of shuffle-set
dislocations is favorable in deformation at thetemperatures under the application of extremely
high stress.
References[1] I. Yonenaga, Eng. Fracture Mechanics 147, 468 (2015).
[2] J. Cochard, I. Yonenaga, M. M’Hamdi, and Z. L. Zhang, J.
Mech. Phys. Sol. 61, 2402 (2014).

IMR KINKEN Research Highlights 2016

Measurement of Internal Electric Fields in Group-III Nitride
Devices by Electroreflectance Spectroscopy

Nitride semiconductor-based devices have strong polarization-induced internal electric fields, which affectthe device performance. To improve the device performance, it is important to design a device structure thattakes the actual internal electric fields into consideration. In this study, the internal electric field was directly
measured by electroreflectance spectroscopy.

Group-III nitride semiconductors exhibit a wurtzite
crystal structure, and they have crystallographic
polarity as a result of this crystal structure. The choiceof crystallographic polarity is one of the key issues
because it influences several properties in terms of thecrystal growth and device characteristics. N-polar
growth facilitates the growth of InGaN with a high InNmolar fraction. In a previous study, N-polar InGaN/
GaN light-emitting diodes (LEDs) operating across thevisible spectrum have been demonstrated [1].
Devices based on group-III nitride semiconductors
often have polarization-induced electric fields, which
affect device performance [2, 3]. In order to realize
high-efficiency devices, the device structure has to be
designed by taking into consideration the actual internal
electric fields induced by the crystallographic
polarization. Up to now, there has been no report on the
direct measurement of such fields. In this study,
electroreflectance (ER) spectroscopy was adopted toinvestigate the actual internal electric fields in III-polar
and N-polar InGaN/GaN LEDs. A comparable study forLEDs fabricated on GaN with different crystal orientationis thus demonstrated for the first time.
In ER measurements, the phases of the ER
spectra are affected with the direction of the internal
electric fields. Schematic diagrams of the energy
band profiles and dielectric constants for III-polar
and N-polar InGaN/GaN quantum wells are shown in
Fig. 1. In InGaN layers with different polarities, thedirections of the built-in electric fields are opposite
each other. Therefore, the phase of an ER signal will
be different depending on the direction of the internal
electric fields. Figure 2 shows the ER spectra for IIIpolar and N-polar LEDs. The phases of the ER
signals from the InGaN layers were opposite eachother in the III-polar and N-polar samples. By fitting
the ER spectra, the internal electric fields were
estimated to be +2.3 MV/cm and −1.1 MV/cm for
N-polar and III-polar LEDs, respectively. In
conclusion, ER spectroscopy is confirmed as aneffective method to directly measure the actualinternal electric fields.

Polarity

N-polarIII-polar
off

off
on

Band
profileon

Modulatedstate εi (ħω)
Steadystate εi (ħω)∆εi (ħω) F (  )E0

 F (  )E0

Fig. 1 Schematic diagrams of energy band profiles anddifference between the steady-state and the modulated
state in the imaginary part of dielectric constants ε i (ħω).

N-polar

InGaN GaN

III-polar
InGaN

GaN

Fig. 2 ER spectra for III-polar and N-polar InGaN/GaN
MQW-LEDs.

References[1] K. Shojiki, T. Tanikawa, J. H. Choi, S. Kuboya, T. Hanada, R.
Katayama, and T. Matsuoka, Appl. Phys. Express 8, 061005 (2015).
[2] T. Aoki, T. Tanikawa, R. Katayama, T. Matsuoka, and K.
Shiojima, Jpn. J. Appl, Phys. 5S, 04EJ09 (2016).
[3] T. Tanikawa, K. Shojiki, R. Katayama, S. Kuboya, and T.
Matsuoka, Jpn. J. Appl, Phys. 5S, 05FJ03 (2016).

Keywords: crystal growth, optoelectronic, spectroscopy
Takashi Matsuoka (Physics of Electronic Materials Division)
E-mail: matsuoka@imr.tohoku.ac.jp
URL: http://www.matsuoka-lab.imr.tohoku.ac.jp/?TOPPAGEIMR KINKEN Research Highlights 201633

Electronic Materials

Design of Rigid Molecular Magnetic Frameworks from a
Combination of Chain and LayerT

he design of three-dimensional (3D) magnetic pathways is a crucial point for the creation of molecularmagnets. We have recently reported a new strategy for constructing 3D magnetic frameworks: π-type donor
molecules, which could make a magnetic pathway, could be combined with π-type acceptor magnetic layers.
This framework was named “π-stacked pillared layer frameworks” (π-stacked PLFs). In this framework, we canintegrate a magnetic pathway, even in the inter-layer direction, through inserted paramagnetic molecules.
Layered magnetic frameworks, which are often
producible in the synthesis of molecular magnets, areuseful for designing hybrid materials with new
functional molecules intercalated between layers;
however, are disadvantage to creating high TC
magnets. We previously reported a new class ofmolecular magnets made from a D2A formulation ofparamagnetic electron-donor (D) units (paddlewheeltype diruthenium(II, II) unit; [Ru2II,II]) and electronacceptor (A) units (tetracyano-p-quinodimethane
derivatives; TCNQRx) [1]. This type of compoundmainly provided layered magnets, which made itdifficult to control inter-layer interactions [2].
Here, we introduce a unique three-dimensionalframework named a “π-stacked pillared layer
framework (π-stacked PLF)” for magnet design. Twotypes of low-dimensional magnet frameworks, a D2A
magnetic layer noted above and a charge transfer[FeCp*2]+TCNQ• – columnar magnet ([FeCp*2]+ =decamethylferrocenium), were integrated in order tofabricate the magnet [3]. [FeCp*2]+TCNQ• – wasreported by Miller et al. and is known to form a
π-stacking
alternatingcolumncomprising
ferromagnetically coupled Coulombic sets [FeCp*2]+
and TCNQ•− with S = ½ [4]. When combined with thelayered D2A, the [FeCp*2]+ unit acts as a π-stacking
pillar for the D2A layers sandwiched between TCNQ•−
moieties, resulting in a π-stacking PLF with theformula [FeCp*2][{Ru2}2TCNQ] (Fig. 1).
The π-stacked PLF compound exhibited aferrimagnetic phase transition at 82 K (Fig. 1), which
could be increased to 107 K by applying a pressureof 12.5 kbar. These results imply that the inserted
spin of [FeCp*2]+ affected the formation of the threedimensional spin arrangement. This synthetic
strategy employing a combination of layers andchains is widely useful for magnet design based onmolecular assemblies.

Fig. 1 (a) Schematic representation of the design strategy
for π-stacked PLF. (b) The layered structure of theobtained π-stacked PLF compound. (c) Temperaturedependence of ac susceptibilities (in-phase χ′ and outof-phase χ′′) of the compound.

[2] H. Miyasaka, T. Izawa, N. Takahashi, M. Yamashita, and K. R.
Dunbar, J. Am. Chem. Soc. 128, 11358 (2006).
[3] H. Fukunaga and H. Miyasaka, Angew. Chem. Int. Ed. 54, 569(2015).

References[1] H. Miyasaka, Acc. Chem. Res. 46, 248 (2013).

[4] G. A. Candela, L. J. Swartzendruber, J. S. Miller, and M. J. Rice,J. Am. Chem. Soc. 101, 2755 (1979).

Keywords: magnetic properties, crystal structure, ferromagnetic
Hitoshi Miyasaka (Solid-State Metal-Complex Chemistry Division)
E-mail: miyasaka@imr.tohoku.ac.jp
URL: http://www.miyasaka-lab.imr.tohoku.ac.jp/

34

IMR KINKEN Research Highlights 2016

IMR KINKEN Research Highlights 2016

Enhanced Output of the Giant Magnetoresistance Junctionfor Hard Disc Drive Applications

Current perpendicular to plane giant magnetoresistance (CPP-GMR) junctions are a key element for future

reading head applications of hard disk drives with an areal recording density of several tera-bit per square
inches, which is being demanded for storing the enormous amount of data present in society. We succeeded
in enhancing the device output of the CPP-GMR junctions using half-metallic Heusler alloy electrodes and a
newly developed Ag-Mg alloy spacer material.
(a)

(b)

Co2(Fe-Mn)Si

Cu electrode

Ferro.
Ag-Mg AlloyV

Non-mag.
Co2(Fe-Mn)Si

50 nm
3 nm

Ferro.

Ag electrodeFig. 1 (a) High-angle annular dark field scanningtransmission electron microscope (HAADF-STEM)
images of a Co2(Fe-Mn)Si/Ag-Mg/Co2(Fe-Mn)Si layered
film, and (b) a CPP-GMR junction. Copyright (2015) The
Japan Society of Applied Physics.
N
N
55

S S
S N

N S
S S

(b)

N
N

5

Device output (mV)(a)
Resistance × Area (mΩµm2)

In the last decade, there has been a drastic
increase in the amount of information handled bysociety. Hard disc drives (HDDs) are one of the major
storage devices with high data retention and low
cost. It is necessary to develop HDDs of several terabit per square inches areal density for supporting thisinformation. Toward this aim, it is necessary toenhance the sensitivity of the reading head devices.
The
current
perpendicular-to-plane
giant
magnetoresistance (CPP-GMR) junction is expected
to have useful applications in future HDDs [1]. It has
been demonstrated that CPP-GMR junctions using
half-metallic cobalt (Co)-based Heusler alloys and asilver (Ag) spacer layer exhibit a large device output
compared with conventional 3d-transition-metalbased junctions [2, 3]. In this work, we have developed
a new non-magnetic spacer layer, Ag-Mg alloy, which
provides a larger device output than the previously
used Ag spacer layer [4].
Figure 1 (a) shows a high-angle annular dark fieldscanning transmission electron microscope (HAADFSTEM) image of a layered film for the CPP-GMR
junction, in which a Ag-Mg spacer layer is sandwichedwith Co2(Fe-Mn)Si Heusler alloy electrodes. Epitaxial
growth and well-defined interfaces are clearly
confirmed by the image. A HAADF-STEM image of ajunction used for measuring the CPP-GMR effect isshown in Fig. 1 (b), and it is confirmed that a submicrometer-scaled junction was successfully
fabricated. A typical result of the CPP-GMR effect isshown in Fig. 2 (a): The resistance of the junction
clearly changed depending on the configuration of
the magnetizations for the Co2(Fe-Mn)Si electrodes,
which is schematically described above the graph.
The performance of the junction was characterized byinvestigating the bias voltage dependence of theoutput voltage (Fig. 2 (b)). The output of the newly
developed Ag-Mg-spacer junction is about 25%
larger than that of the conventional Ag-spacer. Our
material can contribute to the development of next
generation HDD-reading heads.

50

45

40

4
3
2
1

Conventional（Ag Spacer）
New device（Ag-Mg Spacer）

35
-50

0

50

Magnetic field (mT)

0
0

20

40

60

80

Bias voltage (mV)Fig. 2 (a) A CPP-GMR curve of a junction. High resistancestate is observed for the anti-parallel magnetization
configuration. (b) Device outputs as a function of theapplied bias voltage for Ag spacer (diamond) and AgMg spacer (circle) junctions. Copyright (2015) The
Japan Society of Applied Physics.

References[1] M. Takagishi, K. Yamada, H. Iwasaki, H. N. Fuke, and S.
Hashimoto, IEEE Trans. Magn. 46, 2086 (2010).
[2] Y. Sakuraba, M. Ueda, Y. Miura, K. Sato, S. Bosu, K. Saito, M.
Shirai, T. J. Konno, and K. Takanashi, Appl. Phys. Lett. 101,
252408 (2012).
[3] S. Li, Y. K. Takahashi, T. Furubayashi, and K. Hono, Appl. Phys.
Lett. 103, 042405 (2013).
[4] H. Narisawa, T. Kubota, and K. Takanashi, Appl. Phys. Express
8, 063008 (2015).

Keywords: magnetoresistance, half-metal, spintronics
Koki Takanashi (Magnetic Materials Division)
E-mail: koki@imr.tohoku.ac.jp
URL: http://magmatelab.imr.tohoku.ac.jp/

IMR KINKEN Research Highlights 201635

Electronic Materials

Which Crystal Site Do Impurities Adore?

Crystal sites for impurities in lithium niobates (LN) were revealed by combining lattice constant measurementswith thermodynamic constraints. Divalent and trivalent impurities were located at Li sites in LN, whereas
tetravalent impurities were located at Nb sites. This result provides good clues for suppressing point defects,
which enhances optical application of LN.
Lithium niobate (LiNbO3: LN) is a ferroelectricmaterial that shows excellent and versatile
properties. LN has therefore been used as a
substrate for nonlinear optical devices, as well as forsurface acoustic wave devices. LN crystals arenormally grown from the congruent melt to obtain ahomogeneous composition. Because congruent LN(c-LN) contains more Nb than stoichiometric LN,
excess Nb generates intrinsic point defects at Li
sites. In the “Li site vacancy model” (Fig. 1) [1],intrinsic defects are antisite Nb (NbLi) and vacancies(VLi) at Li sites. In particular, NbLi causes
photorefractive damage, which hinders opticalapplication of LN. Regarding this problem, doping
impurities such as MgO were found to be effective
for increasing the damage threshold [1]. However, it
is not fully understood into which site impurities areincorporated and how impurities decrease the NbLi
concentration. Here, the selection of impurity sites
and NbLi behavior in impurity-doped c-LN were
investigated by analyzing the defect structures, i.e.,
configurations of point defects, including impurities
and intrinsic defects. The defect structures were
determined by lattice constant measurements [2]combined with thermodynamic constraints [3].
Several defect structures of impurity-doped LN
are possible depending on the occupancy of the
impurities and the intrinsic defects in crystal sites.
Among them, unfeasible defect structures can be
excludedbyconsidering
thermodynamic
constraints, that is, by evaluating the degrees of
freedom in each crystal site [3]. The degrees of
freedom are obtained by subtracting the number ofthermodynamic constraints from the number ofparameters. The number of parameters at each site
corresponds to the number of elements, including
defects such as antisite defects and vacancies.
Meanwhile, thermodynamic constraints include
mass conservation at each site and the element
exchange in equilibrium [3]. The thermodynamic
analysis revealed that only structures A and B (Fig.
1) are feasible out of the six models.
In structure A, impurities locate at the Li site
Keywords: oxide, doping, defects
Chihiro Koyama and Satoshi Uda (Crystal Chemistry Division)
E-mail: uda@imr.tohoku.ac.jp
URL: http://www.uda-lab.imr.tohoku.ac.jp/index.html

36

IMR KINKEN Research Highlights 2016

Congruent LN [1]

Li siteNb siteO site：Li+：Nb5+：O2：vacancy：Impurity

Impurity-doped LN [2]Structure A
Structure B

Li siteNb siteO siteLi siteNb siteO siteFig. 1 Defect structures of congruent LN and impuritydoped LN.

where VLi and NbLi also exist. In structure B,
Impurities locate at the Nb site while VLi and NbLi
exist at the Li site.
Because the relationship between impurity
concentration and lattice constants for structures A
and B differ, the defect structures can bedifferentiated by analyzing lattice constant variations
with impurity concentration. The results show thatthe defect structure of divalent and trivalent
impurities, (Mg2+, Zn2+, Co2+, Fe3+)-doped c-LN,
employs structure A, whereas tetravalent impurities,(Zr4+, Ti4+, Ce4+)-doped c-LN, has structure B. The
NbLi concentration increases with increasing
tetravalent impurity concentration. In contrast, the
NbLi concentration decreases with increasing
divalent and trivalent impurities. It is the valence ofan impurity that determines the location of impurities,
whether they will be attracted to the Li site or the Nb
site.
References[1] T. Volk and M. Wöhlecke, “Lithium Niobate Defects,
Photorefraction and Ferroelectric Switching” (Springer, 2008).
[2] C. Koyama, J. Nozawa, K. Maeda, K. Fujiwara, and S. Uda, J.
Appl. Phys. 117, 014102 (2015).
[3] S. Uda, “Chapter 4; Stoichiometry of oxide crystals”, Handbookof Crystal Growth, Vol. IA: Fundamentals 2nd Ed. (Elsevier,2014), Edited by T. Nishinaga.

IMR KINKEN Research Highlights 2016

Heaviest Electron Detected by Quantum OscillationsIn heavy fermion physics, Yb compounds attract much interest because they are hole analogues to Cecompounds. Here, the heaviest electrons in YbCu2Si2 were detected by quantum oscillation measurements. It
was found that valence fluctuations play a key role in the heavy electronic state, although YbCu2Si2 at ambientpressure is far from the magnetic quantum critical point.
The de Haas–van Alphen (dHvA) effect, whichis the quantum oscillation in magnetization, is one of
the most powerful experimental probes for detecting
Fermi surfaces. The frequency is proportional to thecross-sectional area of the Fermi surface, and thus
one can precisely determine the topology of the
Fermi surface by rotating the field angle. Effective
masses can also be obtained for each Fermi
surface, meaning that the heavy electronic state
can be directly observed microscopically.
dHvA experiments have been extensively done
for Ce compounds, and the heavy electronic states
have been established. The phenomena arebasically understood in terms of the competition
between the Kondo effect and the Ruderman–
Kittel–Kasuya–Yosida (RKKY) interaction. The
magnetic quantum critical point and the novel
quantum phase, including the superconductivity,
are the central issues in correlated electron systems.
However, in Yb compounds, which are holeanalogues to Ce compounds, Fermi surfaces withheavy electronic states are not very well understood
experimentally because the dHvA experiments
require a high-quality sample, a high field, and low
temperatures.
In this study, we focused on the intermediatevalence-fluctuating compound YbCu2Si2, which has
no magnetic order at ambient pressure. The
electronic specific heat coefficient is 150 mJ/K 2 mol,indicating a heavy electronic state. However, theband calculation, which does not include the manybody effect, resulted in a value of only 15 mJ/K2 mol.
Thus, a heavy Fermi surface with a 10-times-larger
effective mass was expected in the experiments.
We performed the dHvA experiments using ahigh-quality single crystal of YbCu2Si2 under
extreme conditions at temperatures down to 30 mK
and at high fields up to 15 T [1]. Figure 1 shows thedHvA oscillation and its fast Fourier transform (FFT)
spectrum. The dHvA branches denoted as α, β, γ,and ε correspond to the main Fermi surfaces.
Among them, branch β is the heavy Fermi surface,with 43 m0 (m0: rest mass of electron), which(a) YbCu2Si2

H || 13.5o from [001] to [100]40 mK

100 kOe(b)ε150 kOe

H
2ε

3ε γβ
0

5

α
10

15
7

dHvA Frequency (x10 Oe)
Fig. 1 Typical dHvA oscillation and its FFT spectrum in
YbCu2Si2. Branch β has the heaviest cyclotron effective
mass.

corresponds to the cylindrical Fermi surface
centered at the X point in the Brillouin zone for abody-centered tetragonal structure. To ourknowledge, the effective mass of 43 m 0 is theheaviest mass detected experimentally in dHvA
studies of Yb compounds. Interestingly, the heavy
mass in YbCu2Si2 is insensitive to the magnetic field.
This is probably owing to the fact that YbCu2Si2 is avalence-fluctuating compound at ambient pressure,which is far from the magnetic quantum critical point(Pc ≈ 8 GPa).
This work was done in collaboration with F.
Honda, Y. Homma, D. X. Li, R. Settai, H. Harima,
and Y. Onuki.
References[1] D. Aoki, F. Honda, Y. Homma, D. X. Li, R. Settai, H. Harima,
and Y. Onuki, J. Phys. Soc. Jpn. 84, 035002 (2015).

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

IMR KINKEN Research Highlights 201637

Electronic Materials

Effect of Ti Concentration on Chemically Ordered Regions inPb(Mg1/3Nb2/3)O3–PbTiO3 Epitaxial Thin Films

A

lthough controversies still exist, the relaxor phenomenon in Pb(Mg1/3Nb2/3)O3 (PMN) is believed to arise
from a heterogeneous structure consisting of a polar nano-region (PNR) and a chemically ordered region(COR). In the PNR, Mg and Nb are randomly arranged, thus giving rise to frustration, which is the origin of thephenomenon. In the CNR, these elements are ordered, and thus they inhibit the fluctuation. In this study, weinvestigated the effects of Ti substitution on the stability of CORs.
We prepared (1 − x)Pb(Mg1/3Nb2/3)O3 –xPbTiO3(PMN–xPT) thin films by a chemical solution
deposition process on SrTiO3 (001) single-crystal
substrates [1, 2]. The morphotropic phase boundary(MPB) was located at approximately x = 0.6. Our
X-ray diffraction studies revealed that the depositedfilms were pseudocubic up to approximately x = 0.5,
whereas tetragonality increased beyond thiscomposition, suggesting a phase transformation [3].
This means that COR regions may exist below thisvalue, and accordingly, we carried out structural
examinations by using transmission electron
microscopy (TEM).
The electron diffraction (ED) patterns from PMN–xPT specimens with x = 0–0.5 exhibited superlatticereflections at 1/2 1/2 1/2 and other corresponding
positions, indicating the formation of CORs. It wasalso noted that the intensities of the superlatticereflections decreased with increasing Ti content, x.
However, the ED patterns only gave an average
structure; real-space examination was needed.
Figures 1 (a), (b), and (c) show high-angle annulardetector dark-field (HAADF) scanning transmission
electron microscope (STEM) images of PMN–xPT
films with x = 0, 0.4, and 0.5, respectively. (Each set
consists of wide-view images, magnified images, anddiffractograms.) Because an HAADF-STEM image isbasically that of Z-contrast, chemical ordering can bedirectly estimated by the intensity variations of theatomic images. The CORs thus obtained are indicatedby solid rectangles in Fig. 1. As seen in the figure, each
COR extends only up to 2 nm, or several unit cells, andthey are distributed randomly within the film. It is also
evident that an increase in Ti content led to the
suppression of CORs. The driving force for the growthof CORs has its origin in the strain resulting from thedifference of B-site cation radius, Mg2+:0.072 nm andNb5+:0.067 nm, as well as in the electrical neutrality(Mg2+:Nb5+ = 1:2). Overall, it can be said that CORs
have intrinsic structural frustration and that Ti4+
mediates this situation.

Fig. 1 Atomic-resolution HAADF-STEM images of (a)PMN, (b) PMN–0.4PT, (c) PMN–0.5PT. Diffractogramsof the images and magnified images of a typical region
marked with the white broken squares are also
displayed. The solid lines in the HAADF-STEM images
show CORs.

References[1] T. Kiguchi, Y. Misaka, M. Nishijima, N. Sakamoto, N. Wakiya, H.
Suzuki, and T. J. Konno, J. Ceram. Soc. Jpn. 121, 236 (2013).
[2] Y. Misaka, T. Kiguchi, K. Sato, T. Nishimatsu, T. Yamada, N.
Usami, and T. J. Konno, Key Eng. Mater. 582, 19 (2014).
[3] C. Fan, T. Kiguchi, A. Akama, and T. J. Konno, J. Ceram. Soc.
Jpn. 123, 565 (2015).

Keywords: dielectric properties, nanostructure, transmission electron microscopy (TEM)
Takanori Kiguchi (Materials Science of Non-Stoichiometric Compounds Division)
E-mail: tkiguchi@imr.tohoku.ac.jp
URL: http://konno-lab.imr.tohoku.ac.jp/index.html

38

IMR KINKEN Research Highlights 2016

Research Centers

IMR KINKEN Research Highlights 2016

Research Centers

Effects of Re Addition on Hydrogen Isotope Trapping in W
Irradiated with High-energy Fe Ions at Elevated Temperatures
International Research Center for Nuclear Materials ScienceFusion power has been developed as an almost inexhaustible energy source for the future. Nuclear reactionsof hydrogen isotopes, i.e., deuterium (D) and tritium (T), are maintained in high-temperature plasma generated
in a vacuum vessel lined with a refractory material such as tungsten (W). In this study, radiation-induced
defects in W and trapping of D were successfully characterized by positron-annihilation spectroscopy (PAS).
1021

Deuterium retention (D/m2)

Fusion power has been developed as an almost
inexhaustible energy source for future generations.
A large amount of energy (~keV) will be provided
through controlled nuclear fusion reactions of D and
T in high-temperature plasma, together with highenergy He (3.5 MeV) and neutrons (14 MeV). The
inner surfaces of reactor cores will be coated withrefractory materials. Current designs of fusion
reactors use W as a covering material because of its
high melting point.
Tritium is a radioisotope of hydrogen, andhence the release of T from fusion power plants
should be strictly controlled under both normal
operating and accidental conditions. For thispurpose, the amount of T in a vacuum vessel shouldbe less than a certain amount. However, neutron
irradiation of W induces defects, which then traphydrogen isotopes, increasing T retention. The main
objectives of this study were to understand thetrapping of hydrogen isotopes in radiation-induced
defects in W and to develop techniques to mitigate
the radiation effects.
Neutron irradiation of W and W alloys in the
research reactor BR2 has been performed througha collaboration program of the International
Research Center for Nuclear Materials Science.
Deuterium retention in these irradiated specimens
will be examined by exposing the specimens to D
plasma and D2 gas after cooling of neutron-induced
radioactivity.
Prior to the tests of neutron-irradiatedspecimens, the effects of Re addition were
investigated using surrogate irradiation with 6.4 MeV
Fe ions. Disks of W and a W-5Re alloy were irradiatedwith 6.4 MeV Fe ions at 523?1273 K up to 5 dpa(displacement per atom) at the Bragg peak. The
specimens were exposed to D2 gas at 673 K for 10
h. The microstructures of specimens were examinedusing positron-annihilation spectroscopy (PAS),

W
W-5Re
1020

1019

1018
400

600

800
1000
1200
Irradiation temperature (K)1400

Fig. 1 D retention in W and W-5Re irradiated at various
temperatures with 6.4 MeV Fe ions to the peak damagelevel of 0.5 dpa and then exposed to D2 gas at atemperature of 673 K and a pressure of 100 kPa for 10 h.

whereas D retention was measured using nuclear
reaction analysis (NRA).
The values of D retention in W and W-5Re areplotted against irradiation temperature in Fig. 1. The
D retention in W-5Re was comparable to that in W
after irradiation at 523 K. However, after irradiation
at higher temperatures (>1073 K), the D retention in
W-5Re was lower than that in W by one order ofmagnitude. PAS showed that this reduced D
retention in W-5Re was due to faster recovery ofvacancy-type defects (vacancies and vacancy
clusters). These observations suggest that theaddition of Re is effective in reducing trap-site
density after irradiation of high-energy particles [1].
The effects of Re addition after neutron irradiation
will be examined in the near future using thespecimens irradiated in BR2.
References[1] Y. Hatano, K. Ami, V. Kh. Alimov, S. Kondo, T. Hinoki, T.
Toyama, M. Fukuda, A. Hasegawa, K. Sugiyama, Y. Oya, M.
Oyaidzu, and T. Hayashi, Nucl. Mater. Energ. (2016) in press.

Yuji Hatano (Corresponding Author, Hydrogen Isotope Research Center, Organization for Promotion or Research,
University of Toyama)
E-mail: hatano@ctg.u-toyama.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/index.html

40

IMR KINKEN Research Highlights 2016

IMR KINKEN Research Highlights 2016

Single-crystal Growth and Magnetism of New Heavy-fermion
Compound UPd2Cd20
International Research Center for Nuclear Materials Science

we succeeded in growing a high-quality single crystal of the new ternary uranium compound UPd Cd .
2

20

From the electrical resistivity, magnetic properties, and specific heat experiments, UPd2Cd20 was found to be
an antiferromagnetic heavy-fermion compound with a Néel temperature, TN, of 5 K. It also exhibits a large
electronic specific heat coefficient, γ, exceeding 700 mJ/ (mol·K2).
Uranium (U) compounds have been intensively
studied because of interesting phenomena such as
the coexistence of superconductivity and magnetic
and its heavy-fermion (HF) characteristics. The
origin of these characteristic features in U
compounds is responsible for 5f electrons in U
atoms, which is an intermediate state between
localized 4f and itinerant d electron systems.
Recently, a series of compounds with theformula UT2X20 (T: transition metal, X: Al, Zn), which
crystallizes into a cubic CeCr2 Al20 -type structure[Fig. 1(a)] showed HF and metamagnetic behavior[1]. Substituting T and X metals, we can control theground state, i.e., the hybridization effect between
the 5f and conduction electrons. To study thequantum critical point (QCP), we succeeded in
growing a new isostructural compound of UPd2Cd20,
with X = Cd, as shown in Fig. 1(b) [2].
X-ray diffraction experiments revealed that
UPd2Cd20 crystallized into a CeCr2 Al20 -type
structure without impurity phases and with a small
residual resistivity, meaning that the obtained
crystals are high quality. The drop in the magnetic
susceptibility, χ, and the λ-shaped anomaly in thespecific heat, C, in Fig. 2 indicate that UPd2Cd20 is
an antiferromagnet (AF) with TN = 5 K. UPd2Cd20
shows a broad maximum in χ at Tχmax and a large
electronic specific heat coefficient, γ, exceeding
700 mJ/(mol·K2). This value was estimated byextrapolating from C/T (T→0), which is acharacteristic behavior in HF systems. The
coexistence of AF and HF states implies that
UPd2Cd20 is in the vicinity of QCP, and we
succeeded in controlling the hybridization effect in
the UT2X20 system.
To elucidate the AF and HF states in UPd2Cd20,
further experimental measurements such as the deHaas–van Alphen effect and magnetization in highmagnetic fields are in progress.

Fig. 1 (a) Crystal structure of UPd2Cd20. (b) Photograph ofobtained crystal with a large size of 5 × 5 × 3 mm.

Fig. 2 Temperature dependence of the specific heat, C,
indicating a magnetic transition at TN. Inset shows thetemperature dependence of magnetic susceptibility,
indicating a broad maximum at Tχmax and a rapid
decrease at TN.

References[1] Y. Hirose, T. Takeuchi, F. Honda, S. Yoshiuchi, M. Hagiwara, E.
Yamamoto, Y. Haga, R. Settai, and Y. Onuki, J. Phys. Soc. Jpn.
84, 074704 (2015).
[2] H. Doto, Y. Hirose, F. Honda, D. Li, Y. Homma, D. Aoki, and R.
Settai, Physics Proceedia 75, 56 (2015).

Yusuke Hirose (Corresponding Author, Department of Physics, Niigata University)
E-mail: yhirose@phys.sc.niigata-u.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/index.html

IMR KINKEN Research Highlights 201641

Research Centers

One-dimensional Hexagonal LiCoO2 Crystals for Lithium Ion
Battery Application
Cooperative Research and Development Center for Advanced Materials

One-dimensional LiCoO crystals dominantly surrounding characteristic facets were synthesized by using a2

template-mediated flux growth method. The hexagonal cylindrical LiCoO2 crystals were converted from the starting
CoO whiskers. The results from single-particle measurements indicated excellent electrochemical performance.





120

2 m
118

102

118

102

102

Fig. 1 (a) TEM image of 1D LiCoO2 crystal and (b–d)
corresponding SAED patterns.

(120)

(102)

b

(111)

a

c
(118)

Fig. 2 Schematic of atomic arrangements along the (a)CoO [211] direction and the LiCoO2 (b) [211] and (c)[2101] directions.

contribute to the further development of new
advanced materials with a wide range of technologicalapplications.
References[1] N. Zettsu, K. Nishikawa, K. Yubuta, K. Sakurai, Y. Yamamoto, Y.
Mizuno, S. Oishi, and K. Teshima, J. Mater. Chem. A 3, 17016(2015).

Kunio Yubuta (Corresponding Author, Cooperative Research and Development Center for Advanced Materials)
E-mail: yubuta@imr.tohoku.ac.jp
Tadashi Furuhara (Head of Cooperative Research and Development Center for Advanced Materials)
E-mail: crdam@imr.tohoku.ac.jp
URL: http://www.crdam.imr.tohoku.ac.jp/index2.html

42

IMR KINKEN Research Highlights 2016

[2101]LiCoO2 [211]LiCoO2(022)[211]CoO

Recently, much attention has been paid to lithium
ion rechargeable batteries (LIBs) for use as powersources because of their high performance. LiCoO2
is the most widely used cathode material incommercial LIBs owing to its good capacity retention,
rate capability, and high structural reversibility.
The flux method, which is used for crystal growthfrom a liquid phase, is inexpensive, simple, andenvironmentally friendly. In the present study [1], onedimensional (1D) LiCoO2 crystals were grown by the
template-mediated flux growth method. The
precursor CoO (Fm3m, a = 0.4263 nm) whiskers
were synthesized from LiCl and Co powder in a LiCl–KCl mixed flux. After lithiation to obtain CoO whiskers
grown along the <111> direction, the obtained LiCoO2(R3m, a = 0.2819 and c = 1.4063 nm) crystals
maintained the 1D morphology of the precursor CoO
whiskers. The crystal shape was transformed fromflat rectangular (CoO) to hexagonal cylindrical(LiCoO2). In the cylindrical LiCoO2 crystals, numerous
hexagonal plated-shape crystals with sharp
asymmetrical edges were stacked one dimensionally.
Figure 1 shows a TEM image of the 1D LiCoO2
crystal and the corresponding selected area electron
diffraction (SAED) patterns. Ordered diffraction
reflections with no additional spots or diffuse streaks
indicate that the 1D LiCoO2 crystal had highcrystallinity. Figure 2 shows schematics of atomic
arrangements along the [211]CoO, [211]LiCoO2, and[2101]LiCoO2 directions. No significant changes in
the arrangement of Co and O atoms occurred, eventhough the distance of the O–Co–O plane in CoO
decreased somewhat owing to differences in theionic radii of Co2+ in CoO and Co3+ in LiCoO2.
The results from single-particle measurements,
which were carried out in order to study the intrinsic
electrochemical properties of the 1D LiCoO2 crystal,indicated significantly better electrochemical
responses than commercially available LiCoO2.
The shape-controlled crystal growth will

IMR KINKEN Research Highlights 2016

Development of a 25 T Cryogen-free Superconducting Magnet
High Field Laboratory for Superconducting Materials

A

25 T cryogen-free superconducting magnet (25 T-CSM) was successfully developed. The 25 T-CSM
consists of a 14 T low-temperature superconducting (LTS) outer coil and an 11 T high-temperature
superconducting (HTS) inner coil. We succeeded in generating a 24.6 T field within a 1-h energizing time. We
thus broke the record for the world’s highest magnetic field in cryogen-free superconducting magnets.

References[1] S. Awaji, K. Watanabe, H. Oguro, S. Hanai, H. Miyazaki, M.

30
25

Cryogen-freeSuperconducting Manget(Conduction cooling)

20
B (T)

Cryogen-freesuperconducting
magnets(CSMs) are widely used nowadays because they
can be operated without a cryogenic liquid. The
maximum magnetic field generated by CSMs has
increased year by year, as shown in the top imageof Fig. 1, and most of these successes were obtainedby the High Field Laboratory for Superconducting
Materials (HFLSM). Recently, we achieved theworld’s highest magnetic field for CSMs of 24.6 T,
denoted as 25 T-CSM. 25 T-CSM consists of an
inner high-strength Bi2Sr2Ca2Cu3Oy (Bi2223) coil, a
middle high-strength CuNb/Nb3Sn Rutherford cablecoil, and an outer NbTi Rutherford cable coil (bottom
image of Fig. 1) [1]. The outer two low-temperature
superconducting (LTS) coils are connected in series
and are operated by one power supply. The LTS
coils, with a 300 mm bore, generate a 14 T field byan 851 A operating current. The Bi2223 insert coilgenerates 11 T without a background field and 10.6
T with a 14 T background field. The 24.6 T field isobtained in a 52 mm room-temperature bore within
1-h charging by a simultaneous energizing of the
LTS and the HTS coils [2]. The HTS and LTS coils
are separated thermally and cooled by two GM and
two GM/JT cryocoolers, respectively.
The 25 T-CSM enables us a long time in-fieldheat treatment and a high sensitive experiment in
low temperatures. A He-gas flow cryostat, a 3He
refrigerator, and a 3He– 4He dilution refrigerator will
be available. The current–voltage measurements ofsuperconducting wires with a noise levelapproximately one order of magnitude less thanthose of hybrid magnets were confirmed.

15
10
5
IMR-HFLSM
01990 1995 2000 2005 2010 2015 2020
Year

Fig. 1 (top) Progress of cryogen-free superconducting
magnets (CSMs). 25 T-CSM has rewritten the world
record of CSMs. (bottom) Photo of the 25 T-CSM in the
HFLSM annex building.

Takahashi, S. Ioka, M. Sugimoto, H. Tsubouchi, S. Fujita, M.
Daibo, Y. Iijima, and H. Kumakura, IEEE Trans. Appl.
Supercond. 24, 4302005 (2014).
[2] S. Awaji, H. Oguro, K. Watanabe, H. Miyazaki, S. Hanai, T.

Tosaka, and S. Ioka, IEEE Trans. Appl. Supercond. to besubmitted.

Satoshi Awaji and Kazuo Watanabe (Corresponding Authors, High Field Laboratory for Superconducting Materials)
E-mail: awaji@imr.tohoku.ac.jp
Hiroyuki Nojiri (Head of High Field Laboratory for Superconducting Materials)
E-mail: nojiri@imr.tohoku.ac.jp
URL: http://www.hflsm.imr.tohoku.ac.jp/

IMR KINKEN Research Highlights 201643

Research Centers

Scientific Breakthrough toward Creation of New Industrial Materials
Kansai Center for Industrial Materials ResearchInstitute for Materials Research (IMR) has launched the Kansai Center, a comprehensive institute-wide effort
that pairs IMR’s research groups across the innovation spectrum to solve today’s industrial challenges andtransform tomorrow’s global energy problems. The center was established in April 2011 based on an agreement
between IMR, Osaka Prefecture Government, and enterprises in the Kansai area sponsored by the government,
taking over Osaka Center project.

Fig. 1 SEM images of untreated and AO+HW treated
TiNbSn and CP–Ti discs.
200

Pull out strength / MPa

The Kansai Center was established in Osaka as a
special unit in the Institute for Materials Research (IMR),
Tohoku University, in April 2011 based on an agreementwith Osaka Prefecture Government. The Center issponsored by the government (Ministry of Education,
Culture, Sports, Science and Technology) and it took
over the Osaka Center, which carried out its mission from2006 to 2011. The Kansai Center has three missions: first,
to solve technical problems that industries have struggled
to resolve; second, to provide academic output toindustries, with the aim of applying such output to society;and third, to help educate next-generation materials
scientists and researchers in universities and enterprises.
We have organized a bimonthly forum named“Monodukuri Kisokoza,” which focuses on special topics
regarding materials and processing. Projects are
conducted through wide collaborations between thegovernment, universities, research institutions, and otherorganizations. The Center has four venues to cover theKansai area: the Osaka office at Osaka Prefecture
University, the Hyogo office at University of Hyogo, theSendai office in IMR, and Monodzukuri BusinessInformation Center Osaka (MOBIO) in the Creation Core
Higashi-Osaka, a governmental body where sixteen
local universities and one college are located to facilitate
collaboration with various industries.
The Center has developed various materials andprocesses in collaboration with industry, universities, andgovernment organizations. One of them is a bioactive
surface of implant TiNbSn alloy, which has beendeveloped by IMR. Anodic oxidation (AO) andsubsequent hot-water (HW) treatment enhanced apatiteformation after immersing the alloy in Hank’s solution (Fig.
1). A high bonding strength between the TiNbSn alloy
and rabbit femurs was obtained as compared to untreated
TiNbSn from pull-out mechanical tests in animal
experiments [Fig. 2(a)] [1]. Cross-sectional EDX analysis
for the implanted TiNbSn alloy in rabbits over six weeks
revealed incorporation of Ca and P in the TiO2 layer frombone, suggesting diffusion of constituent elements of

(a)

AO+HW
Untreated

150

100

50

0

3

6

Duration after surgery / week

Fig. 2 (a) Failure load 3 and 6 weeks after implantation and(b) schematic illustration of apatite formation after
immersion in Hank’s solution.

animal bone to TiO2, which is responsible for the highbonding strength. Hot-water treatment for the anodized
TiNbSn promoted apatite formation owing to thehydrophilic surface of TiO2 [Fig. 2(b)]. Strong bonding
was attributed to the inter-diffusion of Ca and P between
TiO2 and animal bone. It is concluded that bioactive
properties were imparted to the TiNbSn alloy coated byanodic oxidation of TiO2.
Similar collaboration studies for practical applications
utilizing academic knowledge and industrial technology
have been in progress. The Kansai Center will make aneffort to innovate in the metallic materials industry throughan alliance with partners in the Kansai area and will
promote scientific research of materials science.
References[1] H. Tanaka, Y. Mori, A. Noro, A. Kogure, M. Kamimura, N. Yamada, S.
Hanada, N. Masahashi, and E. Itoi, Plos. (2016) accepted.

Naoya Masahashi (Head of Kansai Center for Industrial Materials Research)
E-mail: masahasi@imr.tohoku.ac.jp
URL: http://www.kansaicenter.imr.tohoku.ac.jp44※Kansai Center has been reorganized in Trans-Regional Corporation Center for Industrial Materials Research since 2016.

IMR KINKEN Research Highlights 2016

IMR KINKEN Research Highlights 2016

Supercomputing to Understand Materials Processing and Materials Properties
Center for Computational Materials ScienceT

he Center for Computational Materials Science supports multiscale supercomputing in materials science. Herein,
we introduce two major activities selected from approximately 120 users. Dr. Deb Nath analyzes solidification
behavior, which is of fundamental importance in manufacturing process, and Dr. Wakeda and Prof. Ogata predictcritical resolved shear stress, a typical mechanical property of alloys.
Interfacial free energy and the stiffness of Cu–Al
alloys obtained by atomistic simulationsa)
Applying classical nucleation theory to a sphericalcrystal embedded in an undercooled melt, one obtains
the interfacial free energy as a function of crystal radius,r [1], σsl = (0.5.ΔT. ΔH.r)/TM (1), where TM is the melting
point and ΔH is the change of enthalpy. Liquid Cu50Al50
alloys are obtained by heating a mixture of Cu and Al ata constant temperature. Then, different sizes of solid
Cu50Al50 spheres are inserted into the liquid Cu50Al50.
The whole system is relaxed for several time steps andthen heated isothermally in order to understand thecritical temperature for each solid Cu50Al50 sphere.
Varying the size of the solid Cu50Al50 sphere in the same
Cu50Al50 liquid cell, the undercooling temperature
versus the inverse of the critical radius of the solid
Cu50Al50 sphere is plotted in Fig. 1. The anisotropy of theinterfacial free energy and its stiffness will be determinedby the capillary fluctuation method [2].

A

priori theoretical prediction of solutestrengthening of iron alloyb)
An a priori theoretical prediction of the solutestrengthening of a metal is required for high throughput
screening of alloys in structural materials design.
Because plastic deformation in a metal is mainly causedby dislocations, the interaction between dislocations
and solute atoms is a crucial factor for controlling thestrength of metals. Here, we focused on iron alloys andconstructed the prediction framework for strengthening
by solute atoms based on atomistic theory. In the caseof bcc iron, the critical resolved shear stress CRSS
(stress at onset of plastic deformation) is dominated byscrew dislocation motion, which is discretized into kink
nucleation and kink migration processes. We evaluatedthe energy barrier for the two processes under the effectof solute atoms using an atomistic model based onsemi-empirical interatomic potentials [3] and calculated
the dislocation velocity by following the thermal
activation theory. The CRSS can be predicted by thedislocation velocity at arbitrary temperatures, soluteconcentrations, and strain rates [4].

Fig. 1 Undercooling temperature as a function of 1/r toobtain the interfacial free energy of the solid–liquidinterface of Cu50Al50.

Fig. 2 The predicted CRSS of pure Fe and Fe–Si alloys [4].

References[3] M. Wakeda, H. Kimizuka, and S. Ogata, J. Japan Inst. Met. Mater.

[1] Y. Watanabe, Y. Shibuta, and T. Suzuki, ISIJ international 50, 1158
(2010).
[2] J.J. Hoyt, M. Asta and A. Karma, Phys. Rev. Lett. 86, 5530 (2001).

77, 409 (2013).
[4] S. Shinzato, M. Wakeda, and S. Ogata, J. Japan Inst. Met. Mater.
80, 197 (2016).

a) Sankar Kumar Deb Nath [Corresponding Author, Computational Materials Research Initiative (CMRI)]
E-mail: debnath@imr.tohoku.ac.jpb) Masato Wakeda1 and Shigenobu Ogata1, 2 (Corresponding Authors, 1Graduate School of Engineering Science,
Osaka U., 2Center for elements strategy initiative for structural materials, Kyoto U.)
E-mail: wakeda@me.es.osaka-u.ac.jp
Tetsuo Mohri (Head of Center for Computational Materials Science)
URL: http://www-lab.imr.tohoku.ac.jp/~ccms/Eng/index.php

IMR KINKEN Research Highlights 201645

Research Centers

Atomic-level Description of Cutting-Edge Energy Materials for a Sustainable Society
Collaborative Research Center on Energy Materials

In order to attain clean and economical energy systems, the Center creates and studies advanced energy materials
with superior functional properties that have important roles in energy generation and consumption. Through joint
efforts in both science and engineering, high-performance energy materials that efficiently convert and transportenergy are investigated.
At our Center, research and development focus on
the atomic-level control of the multiple structure–property relationships of advanced energy materials, aswell as on the design of devices that lead to effective
carrier conversion, high-speed energy transport, andincreasing renewable energy production. This can beachieved by integrated control of spin, electron, ion,hole, and phonon-like carriers.
One of the Center’s research activities is directed
towards the development of materials that can be usedin sustainable gas storage/separation technologies.
This requires precise control of the structure on an
atomic level and accurate analysis of the interactions
that occur during the adsorption process.
In the Material Processing and Social
Implementation Division, we estimate the important
properties of various nanoporous materials using highly
accurate computational methods in order to accelerate
the experimental realization of novel storage media. In
the search for novel functional adsorbents, metal–organic framework (MOF) materials with unprecedented
regular nano-sized spaces have been studied.
Recently, a new soft porous coordination polymer,
Cu2+(5-azidoisophthalate), with adaptable pores that
selectively adsorb CO from a CO/N2 gas mixture wasdiscovered. The key feature of this structure is thepresence of two channels having different pore sizes,
with the size of the small one increasing owing to theinteraction of CO molecules with the Cu2+ sites, as shownin Fig. 1a. This allows one to control the next step of theseparation process. In agreement with the experimental
data, the calculation results showed a remarkable
distinction in adsorption properties of the CO-coordinated
MOF towards CO and N2 separation. The electron
distribution of the CO adsorption process indicatedfavorable attraction between the guest molecule and thesmall channel of the host structure. In the case of N2, theelectron distribution showed repulsion between nitrogenmolecules and the host framework. Thus, high selectivity
is achieved by the synergetic effect of the local interaction
between CO and accessible Cu2+ metal sites and a(a)

CO adsorption

N2 adsorption(b)Fig. 1 (a) Cu2+(5-azidoisophthalate) structure and electron
density contours of CO and N2 adsorbed inside small
channels. (b) Fragment of Zn4(dmf)(ndc)4(ur)2 withurotropine ligand and charge density isosurfaces for
the C2H2, CO2, and CO interactions.

global transformation of the framework [1].
The adsorption properties of the porous Zn4(dmf)(ndc)4(ur)2 structure were also investigated (see Fig. 1b).
This material is a rare example of a microporouscompound with open basic sites decorating the innersurface of the MOF host. It was found that the inclusionof the urotropine ligand into the MOF frameworkenhanced the adsorption of acetylene and carbon
dioxide. Thus, only in the case of the C2H2 molecule,the most favorable attraction with the host is through theformation of a C-H···N hydrogen bond between the Hatoms of acetylene and the N atoms of urotropine [2].
The use of urotropine as a co-bridging ligand in metal–
carboxylate MOFs may therefore result in a variety ofother porous materials with notable basic functionality
derived from non-coordinated N-centers.
References[1] H. Sato, W. Kosaka, R. Matsuda, A. Hori, Y. Hijikata, R. V. Belosludov,
S. Sasaki, M. Takata, and S. Kitagawa, Science 343, 167 (2014).
[2] S. A. Sapchenko, D. N. Dybtsev, D. G. Samsonenko, R. V.
Belosludov, V. R. Belosludov, Y. Kawazoe, M. Schroder, and V. M.
Fedin, Chem. Comm. 51, 13918 (2015).

Rodion Belosludov (Corresponding Author, Collaborative Research Center on Energy Materials)
E-mail: rodion@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/

46

IMR KINKEN Research Highlights 2016

IMR KINKEN Research Highlights 2016

Magnetization Reversal in Perpendicularly Magnetized FePt
Dot and Antidot Arrays
International Collaboration Center (ICC-IMR)F

ePt dot and antidot lattices with diameters 40 nm, 100 nm, and 200 nm were microfabricated by electron beamlithography. Magnetization reversal in these FePt nanoarrays was studied by magneto-optical Kerr effect andmagnetic force microscopy. The FePt dots exhibited superferromagnetic behavior despite their complete isolation.
Magnetic domain imaging revealed that the reversal processes showed a domain wall trap in the antidote lattices.
L10 -FePt alloy is one of the most promisingmaterials for future ultrahigh density magnetic storage
devices
becauseofits
huge
uniaxial
magnetocrystalline anisotropy (Ku = 7 × 107 erg/cm3),
which leads to a high thermal stability of magnetization
at the nanometer scale. The aim of this international
collaboration is to understand the magnetization
reversal processes in FePt thin films, dots, andantidots. By using magneto-optic Kerr microscopy,
we first studied the magnetization reversal in FePt
thin films deposited on MgO (110) substrates
exhibiting in-plane uniaxial magnetic anisotropy. The
domain structure and magnetization reversal processstrongly depended on the film thickness and thedeposition temperature [1].
The magnetization reversal behavior for
perpendicularly magnetized L10 -FePt (001) nanodots
with different interdot spaces was also investigatedby magnetic force microscopy (MFM). The dots,
which were fully isolated, experienced only dipolarinteraction; however, the array with the isolated FePt
dots exhibited domain like features resembling the
behaviourofpercolated
dots,
indicatingsuperferromagnetism in the FePt nanodot array [2].
We also studied the magnetic properties of a“negative” magnetic structure fabricated bylithography to create a mesh of “holes” in a continuous
FePt magnetic thin film. These negative structures
are called “antidots”, and the array of such antidots iscalled “magnetic antidot lattice (MAL)”. MALs are
attracting much interest from the research community
because of their potential lack of superparamagnetic
limit to the bit size (in comparison to dot arrays). The
major question is how a magnetic domain wall (DW)
will behave in an MAL system with periodic defects.
We fabricated MALs of perpendicularly magnetized
FePt with the dimensions of the antidots ranging from
200 nm to 40 nm. MAL arrays with various types oflattices, such as square and honeycomb were

Fig. 1 SEM images of FePt antidot lattices with (a)rectangular and (b) circular holes.

Fig. 2 (a) Morphology of a FePt antidot lattice with thedimension of 200 nm. The image shown in (b) is themagnetic domain structure taken post-remanence after
positive saturation. (c) Magnetic domain imaged near acoercive field of µoH = -0.15 T.

fabricated to study the effect of the lattice pattern on
the magnetization reversal. Scanning electron
microscopy (SEM) indicated that the size and shapeof the antidot lattices were well controlled. Figure 1
shows the SEM images of two representative FePt
MALs on MgO (100) substrates. Figure 2 shows theMFM images of an antidot lattice where the length of
the antidots is 200 nm. It can be observed that theDWs are trapped between the antidot structures.
Under external magnetic field, the domains show
limited expansion within the antidot structures.
References[1] S. Mallick, S. Bedanta, T. Seki, and K. Takanashi, J. Appl. Phys.
116, 133904 (2014).
[2] S. Bedanta, T. Seki, H. Iwama, T. Shima, and K. Takanashi,Appl. Phys. Lett. 107, 152410 (2015).

Subhankar Bedanta [Corresponding Author, National Institute of Science Education and Research (NISER), India]
E-mail: sbedanta@niser.ac.in
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 201647

Research Centers

Materials Science Advanced by Neutron Platform
Center of Neutron Science for Advanced Materials

T

he Center of Neutron Science for Advanced Materials is a unique neutron facility that has the background of
novel material science in IMR. This center is constructing a state-of-the-art polarized neutron spectrometer,
POLANO, at the Japan Proton Accelerator Research Complex (J-PARC/MLF.) To promote neutron science, we
held a workshop and a J-PARC/MLF tour under collaboration with quantum-beam scientists at Tohoku
University.
The Center of Neutron Science for Advanced
Materials (CN-IMR) was established in 2010 with theaim of promoting novel materials science by using
neutrons. The CN-IMR is constructing a newpolarized neutron spectrometer, POLANO, at theJapan Proton Accelerator Research Complex(J-PARC/MLF) [1] as part of a joint project with theHigh Energy Accelerator Research Organization(KEK). The spectrometer will give a unique
opportunity to measure the microscopic state inmaterials with separating pure magnetic correlations
and atomic correlations. The first neutron beam will
be received in 2016FY. The spectrometer will thenbe available for the collaborative research programof IMR.
In order to discuss novel science brought about
through new materials and spectroscopic
measurements, we held a two-day workshop
entitled “Materials Science Advanced by QuantumBeam Platform,” and more than twenty neutronscientists were invited to attend. Information onstate-of-the-art techniques was exchanged among
the participants and future studies utilizing polarized
neutrons at POLANO were discussed.

Fig. 2 A group photo of J-PARC/MLF tour.

Furthermore, a J-PARC/MLF tour was held forstudents and young researchers to provide an
opportunity to visit the large facility and to learn thefundamentals as well as hear about the latest
research in quantum-beam science. Sixteen
students from four laboratories attended the tour.
The lectures on neutron scattering and muon spinrotation techniques were given by four staff members
from Tohoku University and KEK, which covered thehistorical aspects of quantum-beam science at
Tohoku University. Students visited POLANO andsaw the status of the construction. The tour was wellreceived by the participants.
References[1] T. Yokoo, K. Ohoyama, S. Itoh, K. Iwasa, N. Kaneko, J. Suzuki,
M. Ohkawara, K. Aizawa, S. Tasaki, T. Ino, K. Taketani, S.
Ishimoto, M. Takeda, T. Oku, H. Kira, K. Hayashi, H. Kimura,and T. J. Sato, EPJ Web of Conferences 83, 03018 (2015).

Fig. 1 A photo of workshop held in IMR. More than forty
neutron scientists were participated.

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/

48

IMR KINKEN Research Highlights 2016

IMR KINKEN Research Highlights 2016

Artificially Produced Rare-Earth-Free Cosmic Magnet
Research and Development Center for Ultra High Efficiency
Nano-Crystalline Soft Magnetic Material

A hard magnetic L1 –FeNi phase with a chemical order parameter of 0.8 or higher, which is a higher grade0

than that found in cosmic meteorites, was produced artificially by utilizing an alloy design that shortens theformation time from hundreds of millions of years for natural meteorites to less than 300 h.

The present completely rare-earth-free magnet(Fe–Ni–metalloid alloy) with a chemical orderparameter (S) of 0.8 or higher, as shown in Fig. 1 [1],was produced from NANOMET® [2] by partiallyreplacing Fe with Ni. It was produced using thesame production process as NANOMET®.
Surprisingly, the addition of Ni, with a characteristicof soft magnetism by nature to NANOMET®,
changes from a soft magnetic alloy to a hard one(Fig. 2). This change is due to the artificial productionof a highly ordered L10 –FeNi phase in the samples,
where the phase is the same as that found in naturalmeteorites. Crystallization of the amorphous alloy
drastically shortened the production time to 300 hfrom a couple of billion years for natural meteorites.
Opposing characteristics, such as “extremely rapid
quenching (non-equilibrium) and extremely slow
cooling (extreme equilibrium)” and “soft and hardmagnetism” have been linked through serendipity.
The present results open a door for thedevelopment of completely rare-earth-free magnets
with S > 0.8 for the first time. Going forward, we will
come to understand fundamental magnetic
properties before moving on to research anddevelopmentofmaterials
applications.
Subsequently, we will select industrial problems andestablish their solutions. Finally, we are planning tocarry out studies using the magnet in demonstration
motors as soon as possible.

Fig. 2 Magnetic hysteresis (left: black) and dc
demagnetization curves (right: red). Measurement
conditions include applying a maximum magnetic fieldof ~12 kOe perpendicular to the ribbon plane for the M vs
H curve and 10 kOe for the Md(H) vs H curve. Top inset
shows the topographic AFM (Atomic Force Microscope)
image, whereas the bottom inset is the corresponding
magnetic force microscopy (MFM) image demonstrating
the magnetic domains.
Fig. 1 (a) STEM bright-field image and (b) STEM-EDX
elemental mapping. (c, d) Nanobeam electron
diffraction taken from the area marked with circles in
Figs. 1 (a, b). (e) Simulated NBD pattern of the L10 FeNi
structure, with S = 0.8. Here, STEM and EDX stand for
Scanning Transmission Electron Microscope andEnergy Dispersive X-ray spectrometry, respectively.

References[1] A. Makino, P. Sharma, K. Sato, A. Takeuchi, Y. Zhang, and K.
Takenaka, Sci. Rep. 5, 16627 (2015).
[2] A. Makino, T. Kubota, C. Chang, M. Makabe, and A. Inoue, J.
Mag. Mag. Mater. 320, 2499 (2008).

Akira Takeuchi (Corresponding Author, Research and Development Center for Ultra High Efficiency Nano-Crystalline Soft Magnetic Material)
E-mail: takeuchi@imr.tohoku.ac.jp
Akihiro Makino (Head of Research and Development Center for Ultra High Efficiency Nano-Crystalline Soft Magnetic Material)
E-mail: nanoc@imr.tohoku.ac.jp
URL: http://nanoc.imr.tohoku.ac.jp/eng/index.html

IMR KINKEN Research Highlights 201649

Research Centers

Metallic Ground State in an Atomically Thin Superconductor
Induced by an Electric Field
Laboratory of Low-Temperature Materials ScienceE

lectric double-layer transistors composed of an interface between a crystalline solid and an ionic liquid
provide a good opportunity to investigate the intrinsic nature of two-dimensional superconductors. Here, wereport that an ion-gated ZrNCl superconducting surface with an effective thickness of approximately 1.8 nm
reveals a metallic ground state with finite resistance, even in a weak magnetic field.
Recently emerging two-dimensional (2D)superconductors in atomically thin layers atheterogeneous interfaces are attracting growinginterest in condensed matter physics. Thesesystems are highly crystalline with lower normalstate electric resistance. They may therefore show
the intrinsic nature of 2D superconductors, which ishidden by the disorder in conventional metallic thinfilms. An electric double-layer transistor (EDLT),
which is composed of an interface between acrystalline solid and an ionic liquid, may be able toprovide such a clean system because theconduction carriers are induced electrostatically at
the atomically flat surfaces without introducing
extrinsic disorder. Here, we report the transport
properties of a ZrNCl EDLT under a magnetic field,
H [1].
ZrNCl is known as an atomic-layer material withinsulating behavior. In this study, we succeeded inconverting its topmost surface into a superconductor
with a transition temperature, Tc, of 14.5 K and an
effective thickness of approximately 1.8 nm, whichis less than its one-unit-cell thickness, by gating in
the EDLT configuration, as shown in Fig. 1(a). Figure1(b) shows the temperature dependence of the
sheet resistance, Rsheet(T), at a gate voltage, VG, of
6.5 V in magnetic fields perpendicular to the
conducting plane. In this Arrhenius plot, Rsheet(T)exhibits activated behavior just below Tc (dashedlines), which can be well described by theconventional thermal creep phenomenon ofquantum vortices. We found that at low temperatures,on the other hand, each Rsheet(T) curve clearly
deviates from the activated behavior and thencrosses over to temperature-independent behavior
down to the lowest temperature, even at H = 0.05 T,
which is much lower than the upper critical field ofapproximately 2 T. The results imply that a metallic
ground state exists in the wide region of a mixed
state. This can be attributed to the intrinsic vortex

Fig. 1 (a) Schematic of EDLT. (b) Arrhenius plot of the
sheet resistance of a ZrNCl EDLT at VG = 6.5 V for
different magnetic fields perpendicular to the surface.

creep motion driven by quantum mechanicalprocesses, which has been difficult to observe indisordered metallic thin-film superconductors,
resulting in either a superconducting or an insulating
ground state.
Our results indicate that the EDLT provides amodel platform of clean 2D superconductors withweak pinning and disorder.
References[1] Y. Saito, Y. Kasahara, J. Ye, Y. Iwasa, and T. Nojima, Science
350, 409 (2015).

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

50

IMR KINKEN Research Highlights 2016

IMR KINKEN Research Highlights 2016

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 of Alpha-ray

Emitters. This laboratory is one of the most important centers around the world for studying the physical and chemical
properties of radioactive materials such as actinide compounds. Researchers from many of the leading universities andinstitutes all over the country visit this facility every year to prepare a variety of materials and carry out chemical andphysical measurements.

This laboratory has provided a research
environment for the study of 170 radionuclides (RIs) andelements, especially alpha-ray emitters such as actinide
elements, since 1960. The laboratory, originaly locatedin the basement of the old Main Building 1, was moved
to its present location in 1978. The lab’s inventory of RIs,
including actinide elements, is one of the largest among
Japanese universities. The lab functions as an importantsource for the preparation of pure crystals of actinide
compounds, providing them to other universities and to
SORs.
The controlled area of this laboratory consists ofthree chemistry labs, three physical labs, a room forradioactivity measurements, a contamination test room,and storage rooms for RIs and nuclear materials. Eachchemistry lab is equipped with local exhaust ventilation
systems, which enables handling of unsealed radioactive
materials. Gamma-ray spectrometers, a liquid
scintillation counter, and an alpha-ray spectrometer areavailable in the radioactivity measurement room.
Correlated electron phenomena in actinide
intermetallic compounds have attracted attentions. The
formation of a heavy fermion state, where the effective
mass of the conduction carriers become extremely
large as a result of Kondo-type interactions between
magnetic moments derived from the 5f state in actinides
and conduction bands, is one of the central topics being
studied because the high densities-of-state often leadto novel phase transitions, such as unconventional
superconductivity.
The uranium compound URu2Si2 is one of thosecompounds. It is known as an unconventional
superconductor coexisting with an unidentified
electronically ordered state, called a “hidden order” [1].
It is therefore interesting to investigate themodification of the conduction electron behavior upon
introduction of 5f electrons in a metal. This can beaccomplished by detecting changes in the Fermi
surface formed by conduction electrons via the deHaas–van Alphen technique. In fact, it has recently
been demonstrated in a cerium-based system,
CeRu2Si2, with the same crystal structure, where theFig. 1 Fourier transforms of de Haas–van Alphen oscillations
in pure ThRu2Si2 and in uranium-substituted ThRu2Si2. The
frequencies are proportional to the cross sectional areasof the Fermi surfaces.

magnetic moment of the 4f electron in cerium is gradually
incorporated into the Fermi surfaces, leading to theirvolume change, which is interpreted in terms of Kondointeraction [2].
In the case of URu2Si2, however, the situation looks
quite different. Recent attempts to introduce uranium
into the host metal ThRu2Si2 only resulted in a change inthe effective mass of the conduction electrons withoutchanging the volume. A typical experimental result isshown in Fig. 1, where the cross sectional areas areshown both for pure ThRu2Si2 and the dilute alloy(U0.03Th0.97)Ru2Si2 [3]. The enhancement of the
conduction carriers is also reflected in the bulk
properties, such as specific heat [3, 4]. The significantly
different behavior of the actinide system as compared to
the well-known cerium system might reflect novel
characteristics of 5f wave functions in actinides.
References[1] J.A. Mydosh and P.M. Oppeneer, Rev. Mod. Phys. 83, 1301 (2011).
[2] H. Aoki, N. Kimura, and T. Terashima, J. Phys. Soc. Jpn. 83, 072001(2014).
[3] Y. Haga, Y. Matsumoto, N. Tateiwa, E. Yamamoto, N. Kimura, T.
Yamamura, and Z. Fisk, J. Phys.: Conf. Ser. 592, 012036 (2015).
[4] H. Amitsuka and T. Sakakibara, J. Phys. Soc. Jpn. 63, 736 (1994).

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 201651

Research Centers

Improved Analytical Procedures for Highly Sensitive andPrecise Determination of Trace Elements in Metallic Materials
Analytical Research Core for Advanced Materials

In routine elemental analysis, the analytical procedures frequently need to be improved to obtain reliable
results. This paper reports such an improvement, which enables the chemical composition of various metal
and inorganic materials to be determined with better sensitivity and precision.
Elemental analysis is routinely conducted at theAnalytical Research Core for Advanced Materials(ARCAM) by using various instrumental analyticalmethods: inductively coupled plasma atomic
emission spectrometry (ICP-AES), atomic absorption
spectrometry (AAS), etc. A trace amount of alloyedelements in a metallic material is often assayed; forthis purpose, procedures with higher sensitivity andprecision need to be developed. This report
describes two contributions to improving theanalytical procedure that we published in 2015.
A simultaneous internal standard method offlame AAS was developed for determining theamount of alloyed nickel analyte in a steel sample[1]. An AAS instrument at ARCAM has a xenon
short-arc lamp as the continuous radiation source
and a high-resolution echelle monochromator. This
instrument enabled us to measure the analyte andinternal standard absorption simultaneously. In thepresent work, nickel (232.003 nm) and iron (232.036nm) were selected to improve the precision of theanalytical results. Test solutions containing 10 µg
cm-3 of nickel and 500 µg cm-3 of iron were prepared.
Repeated measurements (n = 10) were carried out.
Nickel and iron absorbance values within 1.5–2.7%of the relative standard deviation (RSD) wereobtained. On the other hand, the ratios of theseabsorbance values (Ni/Fe) were 0.7–1.4% of RSD.
Therefore, the present Ni/Fe internal standard
method can be applied for precise nickel
quantification in steel. Certified reference materials
were used for the validation of the present AAS
method: JSS 171-7 containing 0.099 mass% ofnickel and JSS 154-14 containing 0.505 mass% ofnickel. By using accurate iron-matching calibration,
the analytical results of the present internal standard
method agreed with the certified values. In addition,
greater precision was obtained: 0.6–1.0% of RSD.
The liquid–liquid extraction method suggested
in our previous paper [2] was applied to ICP-AES for

determining trace nickel in a cobalt–chromium–molybdenum (CCM) alloy. With a multi-type ICPAES, analysts might be faced with the problem ofspectral interference of CCM matrix components
against trace nickel (< 0.01 mass%). In the present
work, liquid–liquid extraction was employed forsolution preparation in order to measure nickel
emission lines without spectral interference.
Approximately 0.10 g of the CCM alloy was
decomposed with hydrochloric and nitric acids orhydrofluoric acid. The resulting solution was fumedwith 10 cm3 of perchloric acid. By pipetting 35
mass% hydrochloric acid to the fumed solution,
chromium was completely removed. Dried salt withno perchloric acid was dissolved in 20 cm3 of dilutedhydrochloric acid (containing a one-third volume of
distilled water). Liquid-liquid extraction was carriedout two times by using 20 cm3 of 4-methyl-2pentanone containing 20 vol% of trioctylamine.
Perchloric acid (2 cm3) was added to the resulting
aqueous solution. Organic compounds in the
aqueous solution were decomposed by adding
nitric acid continuously. Finally, nickel in a 25.0 cm3
solution with yttrium as an internal standard wasmeasured by ICP-AES. The lower limit ofdetermination was improved from 0.01 mass%(conventional ICP-AES procedure without liquid–
liquid extraction) to 0.0006 mass% (the present
method).
References[1] T. Itagaki, T. Ashino, K. Takada, and K. Wagatsuma, Bunseki
Kagaku 64, 117 (2015).
[2] F. Sakamoto, T. Ashino, and K. Wagatsuma, Bunseki Kagaku
64, 689 (2015).

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

52

IMR KINKEN Research Highlights 2016

Author Index
Name

page

A
Aoki, Dai
Arima, Hiroshi
Awaji, Satoshi

37
9
43

B
Bauer, Gerrit Ernst-Wilhelm
Bedanta, Subhankar
Belosludov, Rodion

47
47
46

C
Chiba, Akihiko13

D
Deb Nath, Sankar Kumar

45

F
Fujita, Masaki
Fujiwara, Kozo
Furuhara, Tadashi

48
18
42

G
Goto, Takashi

12

H
Hashimoto, Kenichiro
Hatano, Yuji
Hirose, Yusuke

30
40
41

I
Imashuku, Susumu
Inoue, Koji
Ishibashi, Shoji
Ito, Akihiko

14
20
16
12

K
Kato, Hidemi
Katsui, Hirokazu
Kiguchi, Takanori
Koyama, Chihiro
Kubo, Momoji
M
Makino, Akihiro
Masahashi, Naoya
Matsuoka, Takashi
Miyamoto, Goro
Miyasaka, Hitoshi

23
12
38
36
19

49
44
33
8
34

Name

page

Mohri, Tetsuo

16, 45

N
Nagai, Yasuyoshi
Nagata, Shinji
Nagumo, Kazuaki
Nakayama, Kenichi
Nambu, Yusuke
Niinomi, Mitsuo
Nojima, Tsutomu
Nojiri, Hiroyuki

20, 40, 41
21
20
52
31
10
50
27, 43O
Ogata, Shigenobu
Orimo, Shin-ichi

45
24, 46

S
Saitoh, Eiji
Sasaki, Takahiko
Satoh, Yuhki
Shimizu, Yasuo
Shiogai, Junichi
Sugiyama, Kazumasa

28
50
22
20
29
9

T
Takagi, Shigeyuki
Takahashi, Ryo
Takanashi, Koki
Takeuchi, Akira
Tretiakov, Oleg

24
28
35
49
26

U
Uda, Satoshi

36

W
Wagatsuma, Kazuaki
Wakeda, Masato
Watanabe, Kazuo

52
45
43

X
Xie, Guoqiang

15

Y
Yamamura, Tomoo
Yonenaga, Ichiro
Yoshikawa, Akira
Yubuta, Kunio

51
32
11
42

IMR KINKEN Research Highlights 201653

Keyword Index
Keyword

page

A
alloy
10, 13anomalous X-ray scattering
9atom probe tomography
8, 20
antiferromagnets
26
B
biological10, 15bulk metallic glass
15
C
ceramic
12, 19crystal growth11, 18, 33
crystal structure
24, 34
cathodoluminescence
14D
defects
32, 36deformation32
devices11
dielectric properties
38
doping36
Dzyaloshinskii-Moriya interaction
26
diffusion
20
E
electron irradiation
14, 22electronic material
28
energy storage
23
F
Fermi surface
37
ferromagnetic
34
field-effect transistor
29
first-principles calculations
16, 24
foam
23
G
glass
9
H
half-metal
35
heavy fermion
37high magnetic field
27
hydride24hydrogen implantation
21
I
ion beam analysis
21
L
luminescence21
Mmagnetic properties
34

54

IMR KINKEN Research Highlights 2016

Keywordpage

magnetoresistance35
mechanical properties
10, 12, 13, 15
molecular dynamics
19
N
nanocluster
8
nanostructure
12, 13, 38
neutron scattering
31
nuclear materials
20, 22O
optical properties
30
optoelectronic
33
organic
30
oxide
36
P
porosity
23
positron annihilation
16
R
radiation effects
11
S
semiconducting
32
simulation
19, 22solar cells
18
spectroscopy
14, 33spin current
28
spin fluctuation
31
spintronics
28, 35steel
8superconducting
27, 29, 30
skyrmions
26Tthin films
29
transmission electron microscopy (TEM) 38
triangular antiferromagnet
31
V
vacancy
16
X
XAFS
9
X-ray scattering
27

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

Editorial Staff:
Misa Yokoyama (IMR), Yoshiko Takahashi (IMR),
and Kaori Kikuchi (IMR)

Printing:
HOKUTO Corporation

Organization
Institute for Materials Research
Tohoku University
2-1-1 Katahira, Aoba-ku, Sendai 980-8577, Japan
Tel. +81-(0)22-215-2144 Fax. +81-(0)22-215-2482
URL: http://www.imr.tohoku.ac.jp/
E-mail: pro-adm@imr.tohoku.ac.jp© IMR June 2016