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論文

XAFS analysis of ruthenium in simulated iron phosphate radioactive waste glass

岡本芳浩; 小林秀和; 塩飽秀啓; 捧賢一; 畠山清司*; 永井崇之

Journal of Non-Crystalline Solids, 551, p.120393_1 - 120393_8, 2021/01

https://doi.org/10.1016/j.jnoncrysol.2020.120393

模擬廃液を含有した鉄リン酸ガラス試料におけるルテニウムの化学状態を、X線吸収微細構造(XAFS)およびイメージングXAFSによって調べた。EXAFS分析の結果、30mol%Fe $_{2}$ O $_{3}$ -P $_{2}$ O $_{5}$ ベースガラスに、廃棄物成分が10wt.%以下の場合では、ルテニウムがガラス相に含まれることを示唆された。他の試料では、ルテニウムは、主に結晶性RuO $_{2}$ として存在することが確認された。イメージングXAFS分析からは、RuO $_{2}$ の析出が確認されたが、全ての試料において、大きさ50m以下の小さいものであった。ホウケイ酸ガラス系で観察されるような、RuO $_{2}$ の凝集体は、本研究における鉄リン酸ガラス試料では確認されなかった。

論文

Direct observation of the magnetic ordering process in the ferromagnetic semiconductor Ga $_{1-x}$ Mn $_{x}$ As via soft X-ray magnetic circular dichroism

竹田幸治; 大矢忍*; Pham, N. H.*; 小林正起*; 斎藤祐児; 山上浩志; 田中雅明*; 藤森淳*

Journal of Applied Physics, 128(21), p.213902_1 - 213902_11, 2020/12

https://doi.org/10.1063/5.0031605

In order to understand the mechanism of the ferromagnetism in Ga $_{1-x}$ Mn $_{x}$ As ((Ga,Mn)As), we have investigated the magnetic behavior on a microscopic level through systematic temperature () and magnetic-field () dependent soft X-ray magnetic circular dichroism (XMCD) experiments at the Mn $L_mathrm{2,3}$ absorption edges. The and dependences of XMCD intensities have been analyzed using a model consisting of the ferromagnetic (FM), paramagnetic, and superparamagnetic (SPM) components. Intriguingly, we have found a common behavior for the ferromagnetic ordering process in (Ga,Mn)As samples with different Mn concentrations and different Curie temperature ( $T_mathrm{C}$ ) values. In particular, the SPM component develops well above $T_mathrm{C}$ , indicating that local FM regions are formed well above $T_mathrm{C}$ . The present findings indicate that the onset of ferromagnetic ordering is triggered by local electronic states around the substitutional Mn ions. Insight into the most representative ferromagnetic semiconductor, (Ga,Mn)As, will be an important step in understanding the mechanism of ferromagnetic ordering in various ferromagnetic semiconductor families.

論文

Determination of atomistic deformation of tricalcium silicate paste with high-volume fly ash

Jee, H.*; Im, S.*; 兼松学*; 鈴木裕士; 諸岡聡; 小山拓*; 町田晃彦*; Bae, S.*

Journal of the American Ceramic Society, 103(12), p.7188 - 7201, 2020/12

https://doi.org/10.1111/jace.17404

被引用回数：0 パーセンタイル：100(Materials Science, Ceramics)

We examined the influence of incorporating high-volume fly ash (FA) on the atomic structure and deformation behavior of calcium silicate hydrates (C-S-H) in tricalcium silicate (C $_{3}$ H) paste upon exposure to external forces. Atomic structural changes and strains under compressive load were assessed using synchrotron in situ high-energy X-ray scattering-based atomic pair distribution function (PDF) analysis. Three different strain types, namely macroscopic strains, measured by a gauge attached to the specimen, strain in reciprocal space, (Bragg peak shifts), and strain in real space (PDF peak shift), were compared. All monitored and calculated strains for C $_{3}$ H-FA (50 wt.% FA) paste were compared with those of pure C $_{3}$ H paste. In the range of 10 , PDF analysis showed that C $_{3}$ H-FA had a similar atomic structure to synthetic C-S-H followed by pure C $_{3}$ H paste. The atomic strain of C $_{3}$ H-FA in real space ( 20 ) was smaller than that of C $_{3}$ H under compression, which suggests that the incompressibility of C-S-H on an atomistic scale is enhanced by fly ash incorporation. This may be caused by increased silicate polymerization of C-S-H due to the additional silicate provided by the fly ash.

論文

Application of an augmentation method to MCR-ALS analysis for XAFS and raman data matrices in the structural change of isopolymolybdates

佐伯盛久*; 蓬田匠; 松村大樹; 斉藤拓巳*; 中西隆造*; 辻卓也; 大場弘則*

Analytical Sciences, 36(11), p.1371 - 1378, 2020/11

https://doi.org/10.2116/analsci.20P147

モリブデンイオンMoO $_{4}$ $^{2-}$ 水溶液に酸を加えると、複数のモリブデン原子が酸素を介して結合したポリモリブデン酸が形成され、さらに酸濃度に応じてポリモリブデン酸の化学形態は大きく変化する。我々は、これまで研究例の少なかった高酸性水溶液中(0.15-4.0M)でのポリモリブデン酸の化学形態を、ラマン分光法およびX線吸収微細構造(XAFS)分光法により調べ、測定したスペクトルを多変量スペクトル分解法(MCR-ALS)により解析した。MCR-ALS解析では実験データ解析により得られるスペクトルの任意性が問題になり、XAFSデータのみの解析ではこれが顕著になるが、XAFSデータとラマンデータを同時にMCR-ALS解析することで、信頼性の高い3成分のXAFSスペクトルを得ることに成功した。構造解析の結果から、硝酸濃度が高くなるにつれポリモリブデン酸の化学種が[Mo $_{36}$ O $_{112}$ (H $_{2}$ O) $_{16}$ ] $^{2+}$ [Mo $_{2}$ O $_{5}$ (H $_{2}$ O) $_{6}$ ] $^{2+}$ [HMoO $_{3}$ (H $_{2}$ O) $_{3}$ ] $^{+}$ へと変化する様子を明らかにした。

論文

Nanoscale structural analysis of Bi $_{0.5}$ Na $_{0.5}$ TiO

米田安宏; 野口祐二*

Japanese Journal of Applied Physics, 59(SP), p.SPPA01_1 - SPPA01_7, 2020/11

https://doi.org/10.35848/1347-4065/aba2c2

被引用回数：0 パーセンタイル：100(Physics, Applied)

放射光全散乱を利用してBi $_{0.5}$ Na $_{0.5}$ TiO (BNT)のナノスケール構造解析を行った。BNTは脱分極温度が低いという問題があるものの、非鉛で優れた圧電特性を持つ物質として期待されている。脱分極はリラクサー同様の散漫的な振る舞いであるため、局所構造解析が必要である。局所構造解析によって化学量論的不均一性と構造不均一性の両方を明らかにした。特に局所構造領域においてはTiのランダムネスが構造の平均化を強く促進していることがわかった。

論文

Insight into Kondo screening in the intermediate-valence compound SmOsSb $_{12}$ uncovered by soft X-ray magnetic circular dichroism

斎藤祐児; 藤原秀紀*; 保井晃*; 門野利治*; 菅原仁*; 菊地大輔*; 佐藤英行*; 菅滋正*; 山崎篤志*; 関山明*; et al.

Physical Review B, 102(16), p.165152_1 - 165152_8, 2020/10

https://doi.org/10.1103/PhysRevB.102.165152

被引用回数：0

Through a high-precision soft X-ray magnetic circular dichroism (XMCD) study of the intermediate-valence compound SmOsSb $_{12}$ , we show our successful approach of revealing unprecedented details of Kondo screening below a characteristic temperature of $T_{0} sim$ 20 K in the paramagnetic phase. The multiplet XMCD structure at the Sm $M_{5}$ edge sensitive to the 4 configuration enabled us to observe a clear difference between the temperature evolution above and below $T_{0}$ with one- and two-component behavior, respectively. Our findings are in strong contrast to the conventional Kondo crossover that coincides with the valence transition, but are qualitatively accounted for by theoretical XMCD predictions combined with the two-fluid phenomenology recently proposed. This work contributes to the large context of Kondo physics that is closely related to quantum criticality in heavy fermion systems.

論文

Fabrication of a novel magnetic topological heterostructure and temperature evolution of its massive Dirac cone

平原徹*; Otrokov, M. M.*; 佐々木泰佑*; 角田一樹*; 友弘雄太*; 日下翔太郎*; 奥山裕磨*; 一ノ倉聖*; 小林正起*; 竹田幸治; et al.

Nature Communications (Internet), 11, p.4821_1 - 4821_8, 2020/09

https://doi.org/10.1038/s41467-020-18645-9

被引用回数：1 パーセンタイル：100(Multidisciplinary Sciences)

We fabricate a novel magnetic topological heterostructure Mn $_{4}$ Bi $_{2}$ Te $_{7}$ /Bi $_{2}$ Te $_{3}$ where multiple magnetic layers are inserted into the topmost quintuple layer of the original topological insulator Bi $_{2}$ Te $_{3}$ . A massive Dirac cone (DC) with a gap of 40-75 meV at 16 K is observed. By tracing the temperature evolution, this gap is shown to gradually decrease with increasing temperature and a blunt transition from a massive to a massless DC occurs around 200-250 K. Magnetic measurements show that there are two distinct Mn components in the system that corresponds to the two heterostructures; MnBi $_{2}$ Te $_{4}$ /Bi $_{2}$ Te $_{3}$ is paramagnetic at 6 K while Mn $_{4}$ Bi $_{2}$ Te $_{7}$ /Bi $_{2}$ Te $_{3}$ is ferromagnetic with a negative hysteresis (critical temperature 20 K). This novel heterostructure is potentially important for future device applications.

論文

Unveiling spin-dependent unoccupied electronic states of Co $_{2}$ MnGe (Ga) film via Ge (Ga) $L_{2,3}$ absorption spectroscopy

吉川智己*; Antonov, V. N.*; 河野嵩*; 鹿子木将明*; 角田一樹; 宮本幸治*; 竹田幸治; 斎藤祐児; 後藤一希*; 桜庭裕弥*; et al.

Physical Review B, 102(6), p.064428_1 - 064428_7, 2020/08

https://doi.org/10.1103/PhysRevB.102.064428

被引用回数：0 パーセンタイル：100(Materials Science, Multidisciplinary)

X-ray absorption spectroscopy (XAS) and X-ray magnetic circular dichroism (XMCD) spectroscopy were applied at the Ge (Ga) $L_{2,3}$ edge to unravel the spin-resolved unoccupied electronic states of Co $_{2}$ MnGe (Ga). Complicated spectral features were observed in both XAS and XMCD spectra. For their interpretation, we compared the experimental XAS and XMCD spectra with the calculated Ge (Ga) 4 and 4 orbital partial density of states. The comparison enabled a qualitative explanation of the XMCD spectra as the difference between the majority and minority-spin unoccupied density of states summed over the 4 and 4 orbitals. Our finding provides a new approach to uncover the spin-split partial density of states above the Fermi level.

論文

Nature of the Dirac gap modulation and surface magnetic interaction in axion antiferromagnetic topological insulator MnBi $_{2}$ Te $_{4}$

Shikin, A. M.*; Estyunin, D. A.*; Klimovskikh, I. I.*; Filnov, S. O.*; Kumar, S.*; Schwier, E. F.*; 宮本幸治*; 奥田太一*; 木村昭夫*; 黒田健太*; et al.

Scientific Reports (Internet), 10, p.13226_1 - 13226_13, 2020/08

https://doi.org/10.1038/s41598-020-70089-9

被引用回数：0 パーセンタイル：100(Multidisciplinary Sciences)

Modification of the gap at the Dirac point (DP) in axion antiferromagnetic topological insulator MnBi $_{2}$ Te $_{4}$ and its electronic and spin structure have been studied by angle- and spin-resolved photoemission spectroscopy (ARPES) under laser excitation at various temperatures, light polarizations and photon energies. We have distinguished both large and reduced gaps at the DP in the ARPES dispersions, which remain open above the Nel temperature of $T_textrm{N}$ = 24.5 K. We propose that the gap above $T_textrm{N}$ remains open due to a short-range magnetic field generated by chiral spin fluctuations. Spin-resolved ARPES, XMCD and circular dichroism ARPES measurements show a surface ferromagnetic ordering for the large gap sample and apparently significantly reduced effective magnetic moment for the reduced gap sample.

論文

Sorption behavior of selenide on montmorillonite

杉浦佑樹; 戸村努*; 石寺孝充; 土井玲祐; Francisco, P. C. M.; 塩飽秀啓; 小林徹; 松村大樹; 高橋嘉夫*; 舘幸男

Journal of Radioanalytical and Nuclear Chemistry, 324(2), p.615 - 622, 2020/05

https://doi.org/10.1007/s10967-020-07092-x

被引用回数：0 パーセンタイル：100(Chemistry, Analytical)

Batch sorption experiments were performed to investigate the sorption mechanism of Se on montmorillonite under reducing conditions in deep geological environments. Based on Eh-pH diagrams and ultraviolet-visible spectra, Se was dissolved as selenide (Se(-II)) anions under the experimental conditions. The distribution coefficients ( $K_{rm d}$ ; m $^{3}$ kg $^{-1}$ ) of Se(-II) indicated ionic strength independence and slight pH dependence. The $K_{rm d}$ values of Se(-II) were higher than those of Se(IV), which also exists as an anionic species. X-ray absorption near edge spectroscopy showed that the oxidation state of Se-sorbed on montmorillonite was zero even though selenide remained in the solution. These results suggest that Se(-II) was oxidized and precipitated on the montmorillonite surface. Therefore, it is implied that a redox reaction on the montmorillonite surface contributed to high $K_{rm d}$ values for Se(-II).

論文

Analysis of atomistic structural deformation characteristics of calcium silicate hydrate in 53-year-old tricalcium silicate paste using atomic pair distribution function

Bae, S.*; Jee, H.*; Suh, H.*; 兼松学*; 城鮎美*; 町田晃彦*; 綿貫徹*; 菖蒲敬久; 諸岡聡; Geng, G.*; et al.

Construction and Building Materials, 237, p.117714_1 - 117714_10, 2020/03

https://doi.org/10.1016/j.conbuildmat.2019.117714

被引用回数：1 パーセンタイル：100(Construction & Building Technology)

Although the atomistic structure and the deformation characteristics of calcium silicate hydrates (C-S-H) are of primary interest in cement chemistry, they have not been fully investigated. In this study, pair distribution function (PDF) analysis was conducted on a 53-year-old fully hydrated tricalcium silicate (C $_{3}$ S) paste using in situ synchrotron high-energy X-ray scattering to probe the atomic structural deformation of C-S-H under external loading. The results were compared with those from our previous PDF study of a 131-day-old C $_{3}$ S paste in order to elucidate the effect of aging on the mechanical characteristics of C-S-H. Three different strains measured by the strain gauge, by the lattice shifts (d-spacing) in the reciprocal space, and by the shift of the interatomic distance (r) in the real space were compared. In the range of r 20 , where most of the information was derived from C-S-H, the 53-year-old C $_{3}$ S paste had a higher overall elastic modulus (18.3 GPa) and better resistance to compressive stress than the 131-day-old C $_{3}$ S paste (elastic modulus: 8.3 GPa). Moreover, it was found that the macroscopic strains of the 53-year-old C $_{3}$ S paste were presumably induced by mechanical deformation such as microcracks at the macroscale. The results provide experimental evidence for the atomistic and mesoscale mechanical behavior of C-S-H in the early and late ages.

論文

Nature of structural instabilities in superconducting SrIrSn $_{13}$

金子耕士; Cheung, Y. W.*; Hu, Y.*; 今井正樹*; 谷奥泰明*; 金川響*; 村川譲一*; 森山広大*; Zhang, W.*; Lai, K. T.*; et al.

JPS Conference Proceedings (Internet), 30, p.011032_1 - 011032_6, 2020/03

https://doi.org/10.7566/JPSCP.30.011032

A quantum critical point appears as a second-order phase transition which takes place at zero temperature. In contrast to heavy-fermion systems in which magnetism often plays a vital role, recent studies revealed that structural instabilities can drive a system to a quantum critical point as well. In quasi-skutterudite (Ca,Sr)Sn $_{13}$ (=Rh, Ir), SrIrSn $_{13}$ exhibits superconductivity around $T_{rm sc}$ 5 K and a structural transition at $T^*{simeq}$ 147 K. Applying physical or chemical pressure on SrIrSn $_{13}$ suppresses rapidly, and a quasi-linear dependence of electrical resistivity, signature of non-Fermi liquid behavior, was observed where extrapolates to 0 K. The isomorphs (CaSr $_{1-x}$ )RhSn $_{13}$ exhibits similar behavior, where the criticality can be reached by 0.9 without external pressure. Neutron scattering experiments in SrIrSn $_{13}$ evidences the second order nature of the structural transition at by the observation of a continuous evolution of superlattice peak below and a gradual increase of critical scattering upon approaching to by cooling. Increase of in (CaSr $_{1-x}$ )RhSn $_{13}$ toward the quantum critical point leads to the systematic variation of the critical exponents of the order parameter. In addition, this substitution induces the phonon softening around the M point towards zero energy revealed by inelastic X-ray scattering experiment. We will present systematic variations in both elastic and inelastic channels upon approaching to the quantum critical point.

論文

Manipulation of saturation magnetization and perpendicular magnetic anisotropy in epitaxial Co $_{x}$ Mn $_{4-x}$ N films with ferrimagnetic compensation

伊藤啓太*; 安富陽子*; Zhu, S.*; Nurmamat, M.*; 田原昌樹*; 都甲薫*; 秋山了太*; 竹田幸治; 斎藤祐児; 小口多美夫*; et al.

Physical Review B, 101(10), p.104401_1 - 104401_8, 2020/03

https://doi.org/10.1103/PhysRevB.101.104401

被引用回数：1 パーセンタイル：31.73(Materials Science, Multidisciplinary)

Spintronics devices utilizing a magnetic domain wall motion have attracted increasing attention, and ferrimagentic materials with almost compensated magnetic moments are highly required to realize the fast magnetic domain wall motion. Here, we report a key function for this purpose in anti-perovskite Co $_{x}$ Mn $_{4-x}$ N films. Perpendicular magnetization emerges for , and the saturation magnetization reaches a minimum value at .

論文

Zeolitic vanadomolybdates as high-performance cathode-active materials for sodium-ion batteries

Zhang, Z,*; Wang, H.*; 吉川浩史*; 松村大樹; 畑尾秀哉*; 石川理史*; 上田渉*

ACS Applied Materials & Interfaces, 12(5), p.6056 - 6063, 2020/02

https://doi.org/10.1021/acsami.9b19808

被引用回数：0 パーセンタイル：100(Nanoscience & Nanotechnology)

Developing new cathode-active materials for rechargeable batteries is important to fulfill the growing demands of energy transformation, storage, and utilization. Zeolitic transition-metal oxides based on vanadomolybdate, constructed by pentagon metal-oxygen clusters as building blocks and metal ions as linkers in a trigonal symmetry, are good candidates for cathodes of Na rechargeable batteries. The material is activated via amorphization of the crystal structure in the ab plane during discharging process, keeping the molecular structure of the building blocks stable, which causes high specific capacity and good cycle performance.

論文

Anomalous small-angle X-ray scattering (ASAXS) study of irradiation-induced nanostructure change in Fe-ion beam irradiated oxide dispersion-strengthened (ODS) steel

熊田高之; 大場洋次郎; 元川竜平; 諸岡聡; 冨永亜希; 谷田肇; 菖蒲敬久; 金野杏彩; 大和田謙二*; 大野直子*; et al.

Journal of Nuclear Materials, 528, p.151890_1 - 151890_7, 2020/01

https://doi.org/10.1016/j.jnucmat.2019.151890

被引用回数：0 パーセンタイル：100(Materials Science, Multidisciplinary)

ステンレス鋼の放射線照射によるナノ構造変化観測用異常分散X線小角散乱(ASAXS)装置を開発した。イオンビーム照射前後のMA956試料の散乱パターンを比較したところ、Cr析出物の形状は全く変化していないことが判明した。

論文

Lattice dynamics in FeSe via inelastic X-ray scattering and first-principles calculations

村井直樹; 福田竜生; 中島正道*; 河村光晶*; 石川大介*; 田島節子*; Baron, A. Q. R.*

Physical Review B, 101(3), p.035126_1 - 035126_6, 2020/01

https://doi.org/10.1103/PhysRevB.101.035126

被引用回数：0 パーセンタイル：100(Materials Science, Multidisciplinary)

非弾性X線散乱を用いたFeSe超伝導体のフォノン研究について報告する。実験的に決定したフォノン分散と非磁性相の密度汎関数理論(DFT)とを比較を行うと、両所の間には顕著な不一致が見られた。FeSeは磁気秩序を示さないにもかかわらず、スピン偏極DFTを用いることによって初めて実験結果は再現される。この解析は、強いスピン揺らぎを内在した常時性状態における近似を与える。

論文

最先端放射光ナノ計測・解析共用拠点(日本原子力研究開発機構)

米田安宏; 吉越章隆; 竹田幸治; 塩飽秀啓; 松村大樹; 菖蒲敬久; 田村和久

まてりあ, 58(12), p.763 - 769, 2019/12

https://doi.org/10.2320/materia.58.763

文部科学省ナノプラットフォーム委託事業において、微細構造解析プラットフォームに属する各実施機関の提供している装置紹介である。

論文

X-ray absorption spectroscopy and magnetocaloric study of Pr $_{1-x}$ Sr $_{x}$ CoO $_{3}$ (00.5)

松村大樹; 辻卓也; 吉井賢資

Materials Chemistry and Physics, 238, p.121885_1 - 121885_5, 2019/12

https://doi.org/10.1016/j.matchemphys.2019.121885

被引用回数：0 パーセンタイル：100(Materials Science, Multidisciplinary)

ペロブスカイトPr $_{1-x}$ Sr $_{x}$ CoO $_{3}$ (00.5)についてX線吸収分光測定を行うとともに、x=0.5で観測される110Kの磁気異常の起源を探るため磁気熱量効果測定を行った。Co吸収端のX線吸収測定からは、xが増えるとともにCoの原子価が増加し、Co-O結合距離が縮まることが分かった。また、CoO $_{6}$ 多面体の歪みも増大することが分かった。Co-O結合距離の縮み方は、xが大きいほど大きいことも分かった。測定温度範囲である17-300Kでは、Co吸収端の吸収スペクトルには異常は見られなかった。磁気熱量効果の結果と合わせ、110Kの異常は磁気構造の変化であることが分かった。

論文

Intrinsic 2D ferromagnetism in V $_{5}$ Se $_{8}$ epitaxial thin films

中野匡規*; Wang, Y.*; 吉田訓*; 松岡秀樹*; 真島裕貴*; 池田啓祐*; 平田靖透*; 竹田幸治; 和達大樹*; 小濱芳允*; et al.

Nano Letters, 19(12), p.8806 - 8810, 2019/12

https://doi.org/10.1021/acs.nanolett.9b03614

被引用回数：8 パーセンタイル：17.8(Chemistry, Multidisciplinary)

The discoveries of intrinsic ferromagnetism in atomically thin van der Waals crystals have opened a new research field enabling fundamental studies on magnetism at two-dimensional (2D) limit as well as development of magnetic van der Waals heterostructures. Here we demonstrate that V $_{5}$ Se $_{8}$ epitaxial thin films grown by molecular-beam epitaxy exhibit emergent 2D ferromagnetism with intrinsic spin polarization of the V 3d electrons although the bulk counterpart is originally antiferromagnetic. Moreover, thickness-dependence measurements reveal that this newly developed 2D ferromagnet could be classified as an itinerant 2D Heisenberg ferromagnet with weak magnetic anisotropy.

論文

Short- and middle-ranges order structures of KNbO nanocrystals

米田安宏; 國定諒一*; 近田司*; 上野慎太郎*; 藤井一郎*; 永田肇*; 尾原幸治*; 和田智志*

Japanese Journal of Applied Physics, 58(SL), p.SLLA03_1 - SLLA03_7, 2019/11

https://doi.org/10.7567/1347-4065/ab37e2

被引用回数：0 パーセンタイル：100(Physics, Applied)

We studied KNbO nanocrystals grown by a solvothermal method. Average and local structures were refined by combining Rietveld and PDF analysis. We found that a rhombohedrally distorted NbO octahedron was maintained in short-range order region, even in the nanocrystals with a cubic average structure. The cubic structure of KNbO nanocrystals were observed as a disordered phase of the rhombohedral structure. The disordered feature can be understood that the structural transformation owing to the particle-size effect is analogous to the temperature-driven phase transition.