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Fe
O
grown on AlO
; Effects of postdeposition annealing studied by XMCD野中 洋亮*; 若林 勇希*; 芝田 悟朗; 坂本 祥哉*; 池田 啓祐*; Chi, Z.*; Wan, Y.*; 鈴木 雅弘*; 田中 新*; 田中 雅明*; et al.
Physical Review Materials (Internet), 7(4), p.044413_1 - 044413_10, 2023/04
被引用回数：0 パーセンタイル：0(Materials Science, Multidisciplinary)We study the electronic and magnetic states of as-grown and annealed FeO(111)/AlO3(111) (
Co, Ni) thin films with various thicknesses grown on Si(111) substrates with the 
-AlO(111)buffer layers by using X-ray absorption spectroscopy (XAS) and X-ray magnetic circular dichroism (XMCD), to investigate magnetically dead layers in these films. Although the magnetically dead layers in the as-grown samples are formed near the interface with the AlO buffer layer, we reveal that ferrimagnetic order is partially recovered by postdeposition annealing at 973 K for 48 hours in air. By analyzing the line shapes of the XAS and XMCD spectra, we conclude that, in the dead layers, there are a significant number of vacancies at the 
sites of the spinel structure, which may be the microscopic origin of the degraded ferrimagnetic order in the FeO thin films.
structure observation of pyroelectric ceramics during power generation cycle川崎 卓郎; 福田 竜生; 山中 暁*; 坂本 友和*; 村山 一郎*; 加藤 孝典*; 馬場 将亮*; 橋本 英樹*; Harjo, S.; 相澤 一也; et al.
Journal of Applied Physics, 131(13), p.134103_1 - 134103_7, 2022/04
被引用回数：1 パーセンタイル：17.38(Physics, Applied)The microscopic origin of the pyroelectric power generation using ferroelectric ceramics for energy harvesting from time-varying waste heat can be understood by conducting 
neutron diffraction measurements. The behavior of the domain orientation and lattice strain in the lead zirconate titanate (PZT)-based ceramics with a tetragonal structure during the novel power generation cycle combining electric field and temperature change were investigated. The [001] domains and the lattice strain of the (111) plane in the direction of parallel to the electric field increase in the process of simultaneous rise in the electric field and temperature, and rapidly decrease in the process of the field drop. The alignment of the domain orientation by the electric field and its randomization by the higher temperature during the cycle are critical features of the current power generation system.
impurity band state as the origin of high Curie temperature in the 
-type ferromagnetic semiconductor (Ga,Fe)Sb武田 崇仁*; 坂本 祥哉*; 荒木 恒星*; 藤澤 唯太*; Anh, L. D.*; Tu, N. T.*; 竹田 幸治; 藤森 伸一; 藤森 淳*; 田中 雅明*; et al.
Physical Review B, 102(24), p.245203_1 - 245203_8, 2020/12
被引用回数：7 パーセンタイル：44.34(Materials Science, Multidisciplinary)(Ga
,Fe
)Sb is one of the promising ferromagnetic semiconductors for spintronic device applications because its Curie temperature (Tc) is above 300 K when the Fe concentration 
is equal to or higher than 0.20. However, the origin of the high Tc in (Ga,Fe)Sb remains to be elucidated. To address this issue, we use resonant photoemission spectroscopy (RPES) and first-principles calculations to investigate the x dependence of the Fe 3 states in (Ga,Fe)Sb ( = 0.05, 0.15, and 0.25) thin films. The observed Fe 2-3 RPES spectra reveal that the Fe-3 impurity band (IB) crossing the Fermi level becomes broader with increasing , which is qualitatively consistent with the picture of double-exchange interaction. Comparison between the obtained Fe-3 partial density of states and the first-principles calculations suggests that the Fe-3 IB originates from the minority-spin (
) 
states. The results indicate that enhancement of the double-exchange interaction between 
electrons with increasing is the origin of the high Tc in (Ga,Fe)Sb.
Kim, J.*; 山中 暁*; 村山 一郎*; 加藤 孝典*; 坂本 友和*; 川崎 卓郎; 福田 竜生; 関野 徹*; 中山 忠親*; 武田 雅敏*; et al.
Sustainable Energy & Fuels (Internet), 4(3), p.1143 - 1149, 2020/03
被引用回数：16 パーセンタイル：64.8(Chemistry, Physical)Waste heat is a potentially exploitable energy source but remains a problem awaiting a solution. To explore solutions for automobile applications, we investigate pyroelectric power generation from the temperature variation of exhaust gas using a novel electro-thermodynamic cycle. Niobium-doped lead zirconate titanate stannate (PNZST) ceramics were applied as pyroelectric materials, and their structural characteristics were investigated. In the driving cycle assessments (JC-08) using real exhaust gas, the maximum power generated was identified as 143.9 mW cm
(777.3 J L
per 1 cycle) over a temperature range of 150-220 
C and an electric field of 13 kV cm-1. The net mean generating power of the total driving cycle was 40.8 mW cm, which is the most enhanced result in our power generating systems to date and 314 times greater than our first report. Materials with sharp transition behaviors with the temperature and electric field are worthy of study with regard to pyroelectric energy harvesting materials, and their corresponding crystal and domain structures were investigated to optimize performance.
ferromagnetic semiconductor (Ga,Fe)Sb; X-ray magnetic circular dichroism and resonance photoemission spectroscopy studies坂本 祥哉*; Tu, N. T.*; 竹田 幸治; 藤森 伸一; Hai, P. N.*; Anh, L. D.*; 若林 勇希*; 芝田 悟朗*; 堀尾 眞史*; 池田 啓祐*; et al.
Physical Review B, 100(3), p.035204_1 - 035204_8, 2019/07
The electronic structure and the magnetism of the ferromagnetic semiconductor (Ga,Fe)Sb, whose Curie temperature can exceed room temperature, were investigated by means of X-ray absorption spectroscopy (XAS), X-ray magnetic circular dichroism (XMCD), and resonance photoemission spectroscopy (RPES). The line-shape analyses of the XAS and XMCD spectra suggest that the ferromagnetism is of intrinsic origin. The orbital magnetic moments deduced using XMCD sum rules were found to be large, indicating that there is a considerable 3
contribution to the ground state of Fe. From RPES, we observed a strong dispersive Auger peak and nondispersive resonantly enhanced peaks in the valence-band spectra. The latter is a fingerprint of the correlated nature of Fe 3 electrons, whereas the former indicates their itinerant nature. It was also found that the Fe 3 states have a finite contribution to the density of states at the Fermi energy. These states, presumably consisting of majority-spin - hybridized states or minority-spin e states, would be responsible for the ferromagnetic order in this material.
ferromagnetic semiconductor (Ga,Fe)Sb; X-ray magnetic circular dichroism and resonance photoemission spectroscopy studies坂本 祥哉*; Tu, N. T.*; 竹田 幸治; 藤森 伸一; Hai, P. N.*; Anh, L. D.*; 若林 勇希*; 芝田 悟朗*; 堀尾 眞史*; 池田 啓祐*; et al.
Physical Review B, 100(3), p.035204_1 - 035204_8, 2019/07
被引用回数：16 パーセンタイル：66.08(Materials Science, Multidisciplinary)The electronic structure and the magnetism of the ferromagnetic semiconductor (Ga,Fe)Sb, whose Curie temperature can exceed room temperature, were investigated by means of X-ray absorption spectroscopy (XAS), X-ray magnetic circular dichroism (XMCD), and resonance photoemission spectroscopy (RPES). The line-shape analyses of the XAS and XMCD spectra suggest that the ferromagnetism is of intrinsic origin. The orbital magnetic moments deduced using XMCD sum rules were found to be large, indicating that there is a considerable 3 contribution to the ground state of Fe. From RPES, we observed a strong dispersive Auger peak and nondispersive resonantly enhanced peaks in the valence-band spectra. The latter is a fingerprint of the correlated nature of Fe 3 electrons, whereas the former indicates their itinerant nature. It was also found that the Fe 3 states have a finite contribution to the density of states at the Fermi energy. These states would be responsible for the ferromagnetic order in this material.
Co
)Fe
O
(x=0-1) layers on Si(111) studied by soft X-ray magnetic circular dichroism若林 勇希*; 野中 洋亮*; 竹田 幸治; 坂本 祥哉*; 池田 啓祐*; Chi, Z.*; 芝田 悟朗*; 田中 新*; 斎藤 祐児; 山上 浩志; et al.
Physical Review Materials (Internet), 2(10), p.104416_1 - 104416_12, 2018/10
被引用回数：10 パーセンタイル：37.66(Materials Science, Multidisciplinary)We study the electronic structure and magnetic properties of epitaxial (NiCo)FeO(111) layers with thicknesses = 1.7 - 5.2 nm grown on AlO
(111)/Si(111) structures. We revealed the crystallographic (octahedral 
or tetrahedral 
) sites and the valences of the Fe, Co, and Ni cations using experimental soft X-ray absorption spectroscopy and X-ray magnetic circular dichroism spectra and configuration-interaction cluster-model calculation.
坂本 祥哉*; 若林 勇希*; 竹田 幸治; 藤森 伸一; 鈴木 博人*; 伴 芳祐*; 山上 浩志; 田中 雅明*; 大矢 忍*; 藤森 淳*
Physical Review B, 95(7), p.075203_1 - 075203_5, 2017/02
被引用回数：9 パーセンタイル：42.75(Materials Science, Multidisciplinary)GeFe (Ge:Fe) shows ferromagnetic behavior up to a relatively high temperature of 210 K and hence is a promising material for spintronic applications compatible with Si technology. We have studied its underlying electronic structure by soft X-ray angle-resolved photoemission spectroscopy measurements and first-principles supercell calculation. We observed finite Fe 3 components in the states at the Fermi level (
) in a wide region of momentum space, and the was located 
0.35 eV above the valence-band maximum of the host Ge. Our calculation indicates that the is also within the deep acceptor-level impurity band induced by the strong -(
) hybridization. We conclude that the additional minority-spin 
electron characteristic of the Fe
state is responsible for the short-range ferromagnetic coupling between Fe atoms.
Mn granular thin films若林 勇希*; 秋山 了太*; 竹田 幸治; 堀尾 眞史*; 芝田 悟朗*; 坂本 祥哉*; 伴 芳祐*; 斎藤 祐児; 山上 浩志; 藤森 淳*; et al.
Physical Review B, 95(1), p.014417_1 - 014417_6, 2017/01
被引用回数：10 パーセンタイル：45.87(Materials Science, Multidisciplinary)Ge
Mn (GeMn) granular thin films are a unique and promising material for spintronic applications owing to their large positive magnetoresistance (MR). The microscopic origin of the MR has not yet been clarified. Here, we develop a method to separately investigate the magnetic properties of the nanoparticles and the matrix, utilizing the extremely high sensitivity of X-ray magnetic circular dichroism (XMCD) to the local magnetic state of each atom. We find that the MR ratio is proportional to the product of the magnetizations originating from the nanoparticles and the matrix. This result indicates that the spin-polarized holes in the nanoparticles penetrate into the matrix and that these holes undergo first order magnetic scattering by the paramagnetic Mn atoms in the matrix, which induces the large MR.
鈴木 良祐*; 松原 雅昭*; 坂本 賢治*; 鈴木 将人*; 白石 泰祐*; 柳原 星児*; 伊沢 悟*; 若井 隆純
Experimental Techniques, 40(1), p.253 - 260, 2016/09
被引用回数：0 パーセンタイル：0.03(Engineering, Mechanical)軸方向に垂直な2つの90度貫通切欠きを持つオーステナイト系ステンレス鋼管の塑性崩壊挙動と強度を調べた。様々なノッチ間距離で二つのノッチ試験片を光塑性フィルムで覆った。試験片には、軸方向の引張荷重と曲げ荷重を任意に組み合わせた荷重を加えた。塑性崩壊挙動を調査するために、試験中に光塑性フリンジパターンの変化が観察された。塑性崩壊強度は、弾完全塑性体に基づくモデルを用いて評価した。実験的な塑性崩壊点での光塑性フリンジパターンは荷重履歴によって異なった。このことから、塑性崩壊挙動は荷重履歴に依存することがわかった。一方、塑性崩壊強度はノッチ間距離にはほとんど依存しなかった。実験的な塑性崩壊は、いくつかの純引張荷重試験でのみ理論塑性点に達する前に発生した。したがって、この研究で使用された弾完全塑性体に基づくモデル解析は、純粋な引張荷重を受けるステンレス鋼管の塑性崩壊には非保守的な推定を与える可能性がある。
Fe若林 勇希*; 坂本 祥哉*; 竹田 幸治; 石上 啓介*; 高橋 文雄*; 斎藤 祐児; 山上 浩志; 藤森 淳*; 田中 雅明*; 大矢 忍*
Scientific Reports (Internet), 6, p.23295_1 - 23295_9, 2016/03
被引用回数：20 パーセンタイル：66.31(Multidisciplinary Sciences)We investigate the local electronic structure and magnetic properties of the group-IV-based ferromagnetic semiconductor, GeFe (GeFe), using soft X-ray magnetic circular dichroism. Our results show that the doped Fe 3 electrons are strongly hybridized with the Ge 4 states, and have a large orbital magnetic moment relative to the spin magnetic moment, namely 
/
0.1. We find that nanoscale local ferromagnetic regions, which are formed through ferromagnetic exchange interactions in the high-Fe-content regions of the GeFe films, exist even at room temperature, well above the Curie temperature of 20 - 100K. We observe the intriguing nanoscale expansion of the local ferromagnetic regions with decreasing temperature, followed by a transition of the entire film into a ferromagnetic state at the Curie temperature.
-type ferromagnetic semiconductor (In,Fe)As:Be studied by X-ray magnetic circular dichroism坂本 祥哉*; Anh, L. D.*; Hai, P. N.*; 芝田 悟朗*; 竹田 幸治; 小林 正起*; 高橋 文雄*; 小出 常晴*; 田中 雅明*; 藤森 淳*
Physical Review B, 93(3), p.035203_1 - 035203_6, 2016/01
被引用回数：18 パーセンタイル：63.01(Materials Science, Multidisciplinary)In order to investigate the mechanism of ferromagnetic ordering in the new -type magnetic semiconductor (In,Fe)As codoped with Be, we have performed X-ray absorption spectroscopy and X-ray magnetic circular dichroism (XMCD) studies. The spectral line shapes suggest that the ferromagnetism is intrinsic, originating from Fe atoms incorporated into the zinc-blende-type InAs lattice. The magnetization curves of Fe measured by XMCD were well reproduced by the superposition of a Langevin function representing superparamagnetic (SPM) behavior of nanoscale ferromagnetic domains and a 
-linear function representing Curie-Weiss paramagnetism even much above the Curie temperatures. The data at 20 K showed a deviation from the Langevin behavior, suggesting a gradual establishment of macroscopic ferromagnetism on lowering temperature. The existence of nanoscale ferromagnetic domains indicated by the SPM behavior suggests spatial fluctuations of Fe concentration on the nanoscale.
岩元 洋介; 義家 敏正*; 吉田 誠*; 中本 建志*; 阪本 雅昭*; 栗山 靖敏*; 上杉 智教*; 石 禎浩*; Xu, Q.*; 八島 浩*; et al.
Journal of Nuclear Materials, 458, p.369 - 375, 2015/03
被引用回数：13 パーセンタイル：73.22(Materials Science, Multidisciplinary)粒子・重イオン輸送計算コードPHITSの100MeV以上の陽子照射による材料損傷の計算手法を検証するため、極低温12Kの環境で125MeV陽子照射による銅の原子のはじき出し断面積に関係する電気抵抗率変化を測定した。実験にあたり、照射した銅サンプルを熱伝導に優れた無酸素銅板により冷却するため、Gifford-McMahon冷凍機を用いた極低温照射システムを開発した。照射サンプルは直径250
m及び純度99.999%の銅線として、電気絶縁及び熱伝導に優れた2枚の窒化アルミニウムセラミック板で挟み込んだ。銅線の電気抵抗率変化は、四端子法を用いて測定した。京都大学FFAG施設でビームフルエンス1.45
10
陽子/cm
の125MeVの陽子を温度12Kで照射した結果、照射前の銅線の電気抵抗29.41
に対し、照射欠陥に伴う1.53という微小な電気抵抗の増加を測定できた。また、PHITSコードを用いて、欠陥生成効率を考慮して銅のはじき出し断面積を算出し、電気抵抗率変化の測定結果から導出した値と比較した。その結果、PHITSの材料損傷の計算手法により、エネルギー100MeV以上の陽子照射による銅のはじき出し断面積を定量的によく再現することがわかった。
-type ferromagnetic semiconductor (In,Fe)As小林 正起*; Anh, L. D.*; Hai, P. N.*; 竹田 幸治; 坂本 祥哉*; 門野 利治*; 岡根 哲夫; 斎藤 祐児; 山上 浩志; 原田 慈久*; et al.
Applied Physics Letters, 105(3), p.032403_1 - 032403_4, 2014/07
被引用回数：6 パーセンタイル：26.85(Physics, Applied)The electronic and magnetic properties of Fe atoms in the ferromagnetic semiconductor (In,Fe)As codoped with Be have been studied by X-ray absorption spectroscopy (XAS) and X-ray magnetic circular dichroism (XMCD) at the Fe 
edge. The XAS and XMCD spectra showed simple spectral line shapes similar to Fe metal, but the ratio of the orbital and spin magnetic moments estimated using the XMCD sum rules was significantly larger than that of Fe metal, indicating a significant orbital moment of Fe 3 electrons in (In,Fe)As:Be. The XMCD intensity as a function of magnetic field indicated hysteretic behavior of the superparamagnetic-like component due to discrete ferromagnetic domains. VC
戸張 博之; 井上 多加志; 谷口 正樹; 柏木 美恵子; 梅田 尚孝; 大楽 正幸; 山中 晴彦; 渡邊 和弘; 坂本 慶司; 栗山 正明*; et al.
Fusion Engineering and Design, 88(6-8), p.975 - 979, 2013/10
被引用回数：1 パーセンタイル：10.69(Nuclear Science & Technology)日本が調達するITER NB機器の1つであるHVブッシングは、コバールをロウ付け接合したセラミックリングとFRPリングからなる2重絶縁管を、5段積み重ねた多芯絶縁フィードスルーである。0.6MPaの絶縁ガス領域と真空の隔壁となるHVブッシングでは、差圧によって生じる圧力荷重や地震荷重並びに自重をFRPリングで支持することが求められる。また、セラミックロウ付け接合部が真空境界となり、ここでは外部に充填する0.6MPaの空気圧に耐える機械強度が求められる。これらの荷重に耐え、安全係数
3.5となる設計案を構築するために、機械構造解析を実施した。FRPについては、発生するせん断力に対する機械強度を増すために繊維を直交させたガラスクロスを周方向に巻いた2次元等方性FRPリングを用いるべきことを明らかにし、またロウ付け接合部については、コバールの形状、固定方法を工夫して応力を低減した。その結果、ITERの要求を満たす構造案を構築できた。
柳原 星児*; 松原 雅昭*; 鈴木 良祐*; 鈴木 将人*; 白石 太祐*; 坂本 賢治*; 若井 隆純
日本機械学会M&M2012材料力学カンファレンス講演論文集(CD-ROM), 2 Pages, 2012/09
The fracture assessment of independent multiple flaws is not developed in the piping for nuclear power in the Japan Society of Mechanical Engineers maintenance standard. In the maintenance standard, an enough examination is not performed about the influence that the load history of the axial tension due to inner pressure and the bending such as the earthquake affects on collapse strength of the piping. This study clarified that the effect of multiple flaws affected on the plastic collapse strength of the stainless steel piping that loaded axial tension and bending independently, and proposed the maximum load evaluation method. Conclusions are as follows: (1) Multiple flaws on piping can be evaluated by the plastic collapse theory of the single flaw, and the flaw can be simplified, and a conservative evaluation of piping be done. (2) The maximum stress can be calculated from the flaw size and mechanical properties of piping and piping size.
白石 太祐*; 松原 雅昭*; 鈴木 良祐*; 鈴木 将人*; 柳原 星児*; 坂本 賢治*; 若井 隆純
日本機械学会M&M2012材料力学カンファレンス講演論文集(CD-ROM), 3 Pages, 2012/09
The aim of this study is to investigate the effect of notch interval on plastic collapse strength of the type 304 stainless steel piping and simplify the flaw assessment method of type 304 stainless steel piping subjected to combined tension and bending. Typical loads applied to type 304 stainless steel piping are axial tension due to internal pressure and bending load caused by external forces. Two 90 degree through-wall notches were machined perpendicular to the axial direction of the pipe with interval, 
, from 1 to 28 mm. The experimental plastic collapse strength of the specimens with single notch and two notches were higher than the theoretical ones of the single notched pipe assumed elastic perfectly plastic body. Therefore, it was clarified that the plastic collapse strengths of type 304 stainless steel pipes with two notches perpendicular to the pipe axis can be evaluated safely using the theoretical ones of the single notched pipe assumed elastic perfectly plastic body.
白石 太祐*; 松原 雅昭*; 鈴木 良祐*; 鈴木 将人*; 若井 隆純; 坂本 賢治*
Proceedings of 5th International Workshop New Methods of Damage and Failure Analysis of Structural Parts (CD-ROM), 6 Pages, 2012/09
The aim of this study is to investigate the effect of notch interval on plastic collapse strength of the type 304 stainless steel piping and simplify the flaw assessment method of type 304 stainless steel piping subjected to combined tension and bending. Typical loads applied to type 304 stainless steel piping are axial tension due to internal pressure and bending load caused by external forces. The plastic collapse strengths of the notched specimen subjected to arbitrary combined axial tension and bending loads were evaluated. Two 90 degree through-wall notches were machined perpendicular to the pipe axis with interval from 1 to 28 mm. It was clarified that the plastic collapse strengths of type 304 stainless steel pipes with two notches perpendicular to the pipe axis can be evaluated safely using the theoretical plastic collapse strength of the pipe with single notch assuming elastic perfectly plastic body.
松原 雅昭*; 林 達也*; 鈴木 将人*; 白石 太祐*; 坂本 賢治*; 若井 隆純
日本機械学会M&M2011材料力学カンファレンス講演論文集(CD-ROM), 2 Pages, 2011/07
本研究では、原子力設備の安全性向上に寄与するため、複数欠陥がステンレス鋼管の塑性崩壊強度に及ぼす影響について調べた。複数欠陥を有する配管の塑性崩壊荷重を知ることは重要である。そこで、簡単のために、複数欠陥を単一欠陥でモデル化することを目的として、単一及び複数の欠陥を有する管に対して、引張及び曲げ荷重が重畳する実験を行った。その結果、(1)複数欠陥を単一欠陥にモデル化することにより保守的に評価可能であることがわかった、(2)いずれの荷重条件においても、並列欠陥は単一欠陥に置き換えて考えることが可能であることがわかった。
戸張 博之; 井上 多加志; 花田 磨砂也; 大楽 正幸; 渡邊 和弘; 梅田 尚孝; 谷口 正樹; 柏木 美恵子; 山中 晴彦; 武本 純平; et al.
Proceedings of 23rd IAEA Fusion Energy Conference (FEC 2010) (CD-ROM), 8 Pages, 2011/03
ITER NBI用高電圧(HV)ブッシングは、ガス絶縁方式である-1MV高圧電源伝送系と真空中に設置する負イオン源及び静電加速器の間の圧力隔壁であり、かつ電力を絶縁導入する重要な機器である。原子力機構では、これまでに5段重ねのHVブッシングの絶縁材に用いる世界最大(外径1.56m)の大口径セラミックの開発に成功した。また、サンプル試験や強度解析を行い、セラミックと金属を一体化する接合技術の開発を進めてきた。そして今回、この大口径セラミックに適用可能な厚肉コバール材を用いたロウ付け接合技術の開発に成功した。さらに、大口径セラミック,金属フランジなどを一体に組み上げHVブッシングの1段分を実サイズで模擬したモックアップを試作し、耐電圧試験を実施した。その結果、1段あたりの定格電圧の20%上回る240kVを1時間以上に渡り安定に保持し、ITER NBIで要求される絶縁性能を実証した。
