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論文

Sommerfeld coefficient enhancement and magnetic short-range order in a hyperkagome 3$$d$$ electron system

社本 真一*; 安井 幸夫*; 吉澤 香奈子*; 野田 幸男*; 高橋 美和子*; 大貫 惇睦*; 芳賀 芳範; 石角 元志*; 山内 宏樹; Huang, T.-C.*; et al.

Physical Review B, 113(23), p.235126_1 - 235126_7, 2026/06

https://doi.org/10.1103/m5pw-ghz3
 被引用回数：0 パーセンタイル：0.00(Materials Science, Multidisciplinary)

$$beta$$-Mn shows a large Sommerfeld constant $$gamma$$ of 70 mJ,$$cdot$$,Mn$$^{-1}$$,$$cdot$$,K$$^{-2}$$, which is one of the largest values in 3$textit{d}$-electron systems. Although the origin has been attributed to the fluctuating magnetic moment, there are no material-dependent systematic studies in the 3$textit{d}$-electron systems except for doped $$beta$$-Mn. The ordered $$beta$$-Mn structure compounds Mn$$_3$$TX (T = Co, Rh, Ir; X = Si, Ge) also exhibit the $$gamma$$ enhancement. We have studied the $$gamma$$ enhancement in Mn$$_3$$TX system. The $$gamma$$ enhancement has been often accompanied with magnetic short-range order. The mechanism of the magnetic short-range order is discussed based on the phase diagrams of Mn$$_3$$TX system. The phase diagrams are categorized in two groups. One group of Mn$$_3$$CoSi and Mn$$_3$$RhSi exhibits the magnetic short-range order above the N$'{e}$el temperature, whereas the others do not. The two groups can be separated by the spin-orbit coupling value, regardless of the cubic lattice parameter.

論文

The Influence of structural dynamics in two-dimensional hybrid organic-inorganic perovskites on their photoluminescence efficiency; Neutron scattering analysis

Rajeev, H. S.*; Hu, X.*; Chen, W.-L.*; Zhang, D.*; Chen, T.*; 古府 麻衣子*; 梶本 亮一; 中村 充孝; Chen, A. Z.*; Johnson, G. C.*; et al.

Journal of the Physical Society of Japan, 94(3), p.034602_1 - 034602_14, 2025/03

https://doi.org/10.7566/JPSJ.94.034602
 被引用回数：3 パーセンタイル：51.84(Physics, Multidisciplinary)

Two-dimensional hybrid organic-inorganic perovskites (HOIPs) have emerged as promising materials for light-emitting diode applications. In this study, by using time-of-flight neutron spectroscopy we identified and quantitatively separated the lattice vibrational and molecular rotational dynamics of two perovskites, butylammonium lead iodide (BA)$$_{2}$$PbI$$_{4}$$ and phenethyl-ammonium lead iodide (PEA)$$_{2}$$PbI$$_{4}$$. By examining the corresponding temperature dependence, we found that the lattice vibrations, as evidenced by neutron spectra, are consistent with the lattice dynamics obtained from Raman scattering. We revealed that the rotational dynamics of organic molecules in these materials tend to suppress their photoluminescence quantum yield (PLQY) while the vibrational dynamics did not show predominant correlations with the same. Additionally, we observed photoluminescence emission peak splitting for both systems, which becomes prominent above certain critical temperatures where the suppression of PLQY begins. This study suggests that the rotational motions of polarized molecules may lead to a reduction in exciton binding energy or the breaking of degeneracy in exciton binding energy levels, enhancing non-radiative recombination rates, and consequently reducing photoluminescence yield. These findings offer a deeper understanding of fundamental interactions in 2D HOIPs and could guide the design of more efficient light-emitting materials for advanced technological applications.

論文

Magnetic excitation in the hyperkagome antiferromagnet Mn$$_{3}$$RhSi

社本 真一; 山内 宏樹; 飯田 一樹*; 池内 和彦*; 金子 耕士; Chen, Y.-S.*; 矢野 真一郎*; Hsu, P.-T.*; Lee, M. K.*; Hall, A. E.*; et al.

Physical Review Research (Internet), 6(3), p.033303_1 - 033303_7, 2024/09

https://doi.org/10.1103/PhysRevResearch.6.033303

Mn$$_{3}$$RhSiの磁気励起は少なくとも0.3から140meVに広がる。200Kでの非弾性散乱強度を積分することで、Mnサイト当たり約5$$mu_{B}$$の磁気モーメントは、約5$$mu_{B}$$であることがわかった。一方で、長距離磁気秩序の磁気モーメントは4Kでわずか2.61$$mu_{B}$$であり、多くの部分が低温まで揺らいでいることがわかった。

論文

Quantum critical behavior of the hyperkagome magnet Mn$$_3$$CoSi

山内 宏樹; Sari, D. P.*; 安井 幸夫*; 坂倉 輝俊*; 木村 宏之*; 中尾 朗子*; 大原 高志; 本田 孝志*; 樹神 克明; 井川 直樹; et al.

Physical Review Research (Internet), 6(1), p.013144_1 - 013144_9, 2024/02

https://doi.org/10.1103/PhysRevResearch.6.013144

$$beta$$-Mn-type family alloys Mn$$_3$$$$TX$$ have three-dimensional antiferromagnetic (AFM) corner-shared triangular network. The antiferromagnet Mn$$_3$$RhSi shows magnetic short-range order (SRO) over a wide temperature range of approximately 500 K above the N$'{e}$el temperature $$T_{rm N}$$ = 190 K. Mn$$_3$$CoSi has the smallest lattice parameter and the lowest $$T_{rm N}$$ in the family compounds. The quantum critical point (QCP) from AFM to the quantum paramagnetic state is expected near a cubic lattice parameter of 6.15 $AA. Although $T_N$$ of Mn$$_3$$CoSi is only 140 K, quantum critical behavior is observed in Mn$$_3$$CoSi as the enhancement of the electronic specific heat coefficient $$gamma$$. We study how the magnetic SRO appears in Mn$$_3$$CoSi by using neutron scattering, $$mu$$SR, and physical property measurements. The experimental results show that the neutron scattering intensity of the magnetic SRO does not change much regardless of the suppressed magnetic moment in the long-range magnetic ordered state compared to those of Mn$$_3$$RhSi. The initial asymmetry drop ratio of $$mu$$SR above $$T_{rm N}$$ becomes small, and the magnetic SRO temperature $$T_{SRO}$$ is suppressed to 240 K. The results suggest that the Mn$$_3$$CoSi is close to the QCP in the Mn$$_3$$$$TX$$ system.

論文

Magnetic properties and electronic configurations of Mn ions in the diluted magnetic semiconductor Ba$$_{1-x}$$K$$_x$$(Zn$$_{1-y}$$Mn$$_y$$)$$_2$$As$$_2$$ studied by X-ray magnetic circular dichroism and resonant inelastic X-ray scattering

鈴木 博人*; Zhao, G.*; 岡本 淳*; 坂本 祥哉*; Chen, Z.-Y.*; 野中 洋亮*; 芝田 悟朗; Zhao, K.*; Chen, B.*; Wu, W.-B.*; et al.

Journal of the Physical Society of Japan, 91(6), p.064710_1 - 064710_5, 2022/06

https://doi.org/10.7566/JPSJ.91.064710
 被引用回数：5 パーセンタイル：43.12(Physics, Multidisciplinary)

The magnetic properties and the electronic excitations of the new diluted magnetic semiconductor Ba$$_{1-x}$$K$$_x$$(Zn$$_{1-y}$$Mn$$_y$$)$$_2$$As$$_2$$ have been studied by X-ray magnetic circular dichroism (XMCD) and resonant inelastic X-ray scattering (RIXS). The sum rule analysis of the XMCD spectra indicates that the Mn atoms are in the high-spin configurations of $$d^5$$, whereas the presence of competing ferromagnetic and antiferromagnetic interactions between the Mn ions reduces the net spin moment. Based on a comparison of the RIXS line shapes with those of Ga$$_{1-x}$$Mn$$_x$$As, it is concluded that the ground state of Mn in Ba$$_{1-x}$$K$$_x$$(Zn$$_{1-y}$$Mn$$_y$$)$$_2$$As$$_2$$ consists of both the $$3d^5 underline{L}$$ and $$3d^5$$ electron configurations.

論文

Demonstration of long-pulse acceleration of high power positive ion beam with JT-60 positive ion source in Japan-Korea joint experiment

小島 有志; 花田 磨砂也; Jeong, S. H.*; Bae, Y. S.*; Chang, D. H.*; Kim, T. S.*; Lee, K. W.*; Park, M.*; Jung, B. K.*; 藻垣 和彦; et al.

Fusion Engineering and Design, 102, p.81 - 87, 2016/01

https://doi.org/10.1016/j.fusengdes.2015.11.033
 被引用回数：8 パーセンタイル：51.92(Nuclear Science & Technology)

原子力機構では、JT-60SAで利用する中性粒子入射装置の実現に向けて、高出力長パルスの正イオン源を開発中であり、今回、JT-60SAの要求値を超える2MWの正イオンビームを100秒間生成することに成功した。本実験は、「日本原子力研究開発機構と韓国国立核融合研究所との間の核融合研究開発に関する協力のための取決め」に基づいた共同実験として韓国原子力研究院において実施した。その結果、ビームの生成時間が30秒を超えると、イオンを生成するための放電ガス圧の変化がビーム電流値の時間的変化を引き起こすことが分かった。さらに、ビーム電流が変化するため、ビーム電流値とイオン源加速電極の電圧配分で決まるビームの収束性が時間とともに悪化していることが判明した。この収束性の悪化により、ビームの一部が加速電極に衝突し、電極の熱負荷が過大となり、加速電極間で絶縁破壊が発生し、ビーム生成時間が制限されていることが初めて分かった。そこで、イオン源の動作ガス圧を制御してビーム電流の時間的変動を低減するとともに、加速電極電圧の配分を細かく調整することでビーム収束性の悪化を抑えて熱負荷を低く保ち、2MWのビームを100秒間生成することに成功した。これらの長時間運転手法の開発と実証により、JT-60SAでの100秒運転に見通しがついた。

論文

Magnetic correlations in Ho$$_{x}$$Tb$$_{2-x}$$Ti$$_{2}$$O$$_{7}$$

Chang, L.-J.; Schweika, W.*; Kao, Y.-J.*; Chou, Y. Z.*; Per${ss}$on, J.*; Br$"u$ckel, T.*; Yang, H. C.*; Chen, Y. Y.*; Gardner, J. S.*

Physical Review B, 83(14), p.144413_1 - 144413_7, 2011/04

https://doi.org/10.1103/PhysRevB.83.144413
 被引用回数：9 パーセンタイル：36.44(Materials Science, Multidisciplinary)

Polycrystalline samples of Ho$$_{x}$$Tb$$_{2-x}$$Ti$$_{2}$$O$$_{7}$$ (0 $$<$$ $$x$$ $$<$$ 2) have been prepared and characterized for their structural and magnetic properties. The parent compounds of this solid solution are the spin ice Ho$$_{2}$$Ti$$_{2}$$O$$_{7}$$ and the spin liquid Tb$$_{2}$$Ti$$_{2}$$O$$_{7}$$. The results of specific heat, elastic and inelastic neutron scattering measurements suggest that the very strong single-ion effects of Ho$$_{2}$$Ti$$_{2}$$O$$_{7}$$ and Tb$$_{2}$$Ti$$_{2}$$O$$_{7}$$ persist in the Ho$$_{x}$$Tb$$_{2-x}$$Ti$$_{2}$$O$$_{7}$$ (0 $$<$$ $$x$$ $$<$$ 2) solid solution, whereas the Tb-Ho correlations are weak, resulting in small shifts in the energy scales but with no dramatic effect on the bulk properties.

論文

Mixed-state Hall effect and flux pinning in Ba(Fe$$_{1-x}$$Co$$_{x}$$)$$_{2}$$As$$_{2}$$ single crystals (x = 0.08 and 0.10)

Wang, L. M.*; Sou, U.-C.*; Yang, H. C.*; Chang, L.-J.; Cheng, C.-M.*; Tsuei, K.-D.*; Su, Y.*; Wolf, T.*; Adelmann, P.*

Physical Review B, 83(13), p.134506_1 - 134506_8, 2011/04

https://doi.org/10.1103/PhysRevB.83.134506
 被引用回数：29 パーセンタイル：71.04(Materials Science, Multidisciplinary)

Longitudinal and Hall resistivities, scaling behavior, and magnetizations are examined to study the effect of flux pinning in Ba(Fe$$_{1-x}$$Co$$_{x}$$)$$_{2}$$As$$_{2}$$ (BFCA) single crystals with x = 0.08 and 0.10. Larger values of activation energy, critical current density, and pinning force are obtained in BFCA with x=0.10, indicating relatively strong pinning. The correlation between longitudinal and Hall resistivities shows the scaling behavior of $$rho_{xy} propto {(rho_{xx})}^{beta}$$ with exponents $$beta$$ = 3.0-3.4 and 2.0$$pm$$0.2 for BFCA crystals with x = 0.08 and 0.10, respectively. Furthermore, the normal-state Hall angle is also observed, and is explained by the Anderson theory. The results are analyzed and coincide with the theory, including the pinning-induced backflow effect and plastic flow mechanism in vortex dynamics.

論文

Study of ion-beam-induced damage and luminescence properties in terbium-implanted AlGaN

Park, J.-H.*; 若原 昭浩*; 岡田 浩*; 古川 雄三*; Kim, Y.-T.*; Chang, H.-J.*; Song, J.*; Shin, S.*; Lee, J.-H.*; 佐藤 真一郎; et al.

Japanese Journal of Applied Physics, 49(3), p.032401_1 - 032401_5, 2010/03

https://doi.org/10.1143/JJAP.49.032401
 被引用回数：1 パーセンタイル：5.09(Physics, Applied)

Terbium (Tb) ions were implanted into Al$$_{0.35}$$Ga$$_{0.65}$$N epitaxial layers at room temperature to investigate ion-beam-induced damage and luminescence properties at various doses of $$1times 10^{12}$$ - $$2.8times 10^{16}$$ Tb/cm$$^2$$. Rutherford backscattering spectrometry/channeling (RBS/channeling) reveals that on-beam-induced damage level steeply increases and that the damage cannot be fully recovered even after rapid thermal annealing at 1100 $$^{circ}$$C, when the dose exceeds $$5times 10^{14}$$ Tb/cm$$^2$$. On the other hand, cathodoluminescence (CL) intensity related to Tb$$^{3+}$$ transitions increased initially and saturated above a dose of $$1times 10^{13}$$ Tb/cm$$^2$$. The results suggest that Tb-related luminescence properties are much susceptible to defects and nonradiative defects, namely, Tb-defect complexes, are formed under low-dose conditions even at a very low structural defect density.

論文

Electronic structure and magnetism of the diluted magnetic semiconductor Fe-doped ZnO nanoparticles

片岡 隆史*; 小林 正起*; 坂本 勇太*; Song, G. S.*; 藤森 淳*; Chang, F.-H.*; Lin, H.-J.*; Huang, D. J.*; Chen, C. T.*; 大河内 拓雄*; et al.

Journal of Applied Physics, 107(3), p.033718_1 - 033718_7, 2010/02

AA2009-0977.pdf:1.0MB

https://doi.org/10.1063/1.3294620
 被引用回数：58 パーセンタイル：85.74(Physics, Applied)

We have studied the electronic structure of Fe-doped ZnO nanoparticles, which have been reported to show ferromagnetism at room temperature, by X-ray photoemission spectroscopy (XPS), resonant photoemission spectroscopy (RPES), X-ray absorption spectroscopy (XAS) and X-ray magnetic circular dichroism (XMCD). From the experimental and cluster-model calculation results, we find that Fe atoms are predominantly in the Fe$$^{3+}$$ ionic state with mixture of a small amount of Fe$$^{2+}$$ and that Fe$$^{3+}$$ ions are dominant in the surface region of the nanoparticles. It is shown that the room temperature ferromagnetism in the Fe-doped ZnO nanoparticles is primarily originated from the antiferromagnetic coupling between unequal amounts of Fe$$^{3+}$$ ions occupying two sets of nonequivalent positions in the region of the XMCD probing depth of $$sim$$2-3 nm.

論文

Electronic structure of Ga$$_{1-x}$$Cr$$_{x}$$N and Si-doping effects studied by photoemission and X-ray absorption spectroscopy

Song, G.*; 小林 正起*; Hwang, J. I.*; 片岡 隆*; 滝沢 優*; 藤森 淳; 大河内 拓雄; 竹田 幸治; 岡根 哲夫; 斎藤 祐児; et al.

Physical Review B, 78(3), p.033304_1 - 033304_4, 2008/07

https://doi.org/10.1103/PhysRevB.78.033304
 被引用回数：8 パーセンタイル：35.20(Materials Science, Multidisciplinary)

The electronic structure of the magnetic semiconductor Ga$$_{1-x}$$Cr$$_{x}$$N, and the effect of Si doping on it have been investigated by photoemission and soft X-ray absorption spectroscopy. We have confirmed that Cr in GaN is predominantly trivalent when substituting for Ga and that Cr 3$$d$$ states appear within the band gap of GaN just above the N 2$$p$$-derived valence-band maximum. As a result of Si doping, downward shifts of the core levels (except for Cr 2$$p$$) and the formation of new states near the Fermi level were observed, which we attribute to the upward chemical-potential shift and the formation of a small amount of Cr$$^{2+}$$ species caused by electron doping. Possibility of Cr-rich cluster growth by Si doping are discussed based on the spectroscopic and magnetization data.

論文

Photocathodes for the energy recovery linacs

Rao, T.*; Burrill, A.*; Chang, X. Y.*; Smedley, J.*; 西谷 智博; Hernandez Garcia, C.*; Poelker, M.*; Seddon, E.*; Hannon, F. E.*; Sinclair, C. K.*; et al.

Nuclear Instruments and Methods in Physics Research A, 557(1), p.124 - 130, 2006/02

https://doi.org/10.1016/j.nima.2005.10.112
 被引用回数：67 パーセンタイル：96.12(Instruments & Instrumentation)

近年、次期光源や高エネルギー核物理学に用いるエネルギー回収型線形加速器(ERL)の利用が注目を浴びている。ERLが要求する電子源性能は、電流値、電流密度、繰り返し、温度や加速勾配など広範囲に渡る。これらの性能を実現する電子源として、光陰極電子源が重要な役割を果たすと考えられている。本論文では、ERLを実現しうる二次電子放出型、セシウム付加ディスペンサー型、フィールドエミッタ型や超格子半導体の光陰極電子源について概論を提供する。

報告書

Separation of technetium from neutron irradiated molybdenum

上野 馨; Chang, C.-T.*

JAERI 1036, 3 Pages, 1962/11

JAERI-1036.pdf:0.19MB

塩化テトラフェニルアルソニウムを用いる$$^{99m}$$Tcの分離法を研究し、次のことがわかった。$$^{99}$$Mo-$$^{99m}$$Tcを含む5%以下のアンモニヤ水溶液-0.1M塩化テトラフェニルアルソニウムのクロロホルム溶液系で、溶媒抽出をすれば、$$^{99m}$$Tcは$$^{99}$$Moを含まずに、よく有機層に抽出される。この方法で、中性子照射をした$$^{99}$$Moより、$$^{99m}$$Tcを定量的に、放射化学的に純粋に抽出することができる。抽出されたテクネチウムは6.0時間の半減期で減衰し、$$^{99m}$$Tcの減衰によく一致している。

口頭

Decimeter-scale laboratory studies of thermal, mechanical, hydrological and chemical processes in near-field systems of generic geological waste repositories

Hu, Q. H.*; Zhang, T.*; Shen, Y. Q.*; 舘 幸男; 深津 勇太; Borglin, S.*; Chang, C.*; Hampton, J.*

no journal, , 

In a deep geological repository of high-level nuclear wastes, the near-field systems consist of waste packages, buffer materials, and natural barrier systems. It is expected that the initial thermal loading after waste emplacement will last several hundred years. It is important to investigate the effects of this thermal loading on the near-field components under in situ stress conditions, in terms of thermal-hydrological-mechanical-chemical (THMC) processes and subsequent radionuclide retention and migration. Preliminary tests have been performed via integrated combinations of buffer materials and host rocks, at nm-dm scales, subjected to a range of elevated temperatures under true-triaxial conditions, which is complemented by a suite of nano-petrophysical characterization approaches such as small-angle neutron/X-ray scattering techniques to quantify total pore space and sample size-dependent effective porosity. For multiple-approach radionuclide retention and migration tests before- and after-THMC experiments, a complementary range of tests will include batch, column, and gas diffusion for granular samples, as well as gas/liquid diffusion and fractured core transport tests for intact rock samples under different temperature and pressure conditions.

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