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論文

Microscopic origin of the spin-reorientation transition in the kagome topological magnet TbMn$$_{6}$$Sn$$_{6}$$

Huang, Z.*; Wang, W.*; Ye, H.*; Bao, S.*; Shangguan, Y.*; Liao, J.*; Cao, S.*; 梶本 亮一; 池内 和彦*; Deng, G.*; et al.

Physical Review B, 109(1), p.014434_1 - 014434_9, 2024/01

TbMn$$_{6}$$Sn$$_{6}$$ is a correlated topological magnet with a Mn-based kagome lattice, in which a Chern gap opens at the Dirac point at low temperatures. The magnetic moment direction of the ferrimagnetic order changes from in the kagome plane to the out-of-plane upon cooling, which is essential for generating the Chern gap, but the underlying mechanism for the spin reorientation remains elusive. Here, we investigate the spin-reorientation transition in TbMn$$_{6}$$Sn$$_{6}$$ using neutron scattering. We provide direct evidence for the spin-reorientation transition and unveil the coexistence of two Tb modes at 200 K. To account for these results, we put forward a model based on SU(N) spin-wave theory, in which there is a temperature evolution of the ground state Tb $$4f$$ orbitals, driven by the crystalline electric field, single-ion anisotropy, and exchange interactions between Tb and Mn ions. Our findings shed light on the complex magnetism of TbMn$$_{6}$$Sn$$_{6}$$, despite its relatively simple ground state magnetic structure, and provide insights into the mechanisms for tuning magnetic topological materials.

論文

Pressure-modulated magnetism and negative thermal expansion in the Ho$$_2$$Fe$$_{17}$$ intermetallic compound

Cao, Y.*; Zhou, H.*; Khmelevskyi, S.*; Lin, K.*; Avdeev, M.*; Wang, C.-W.*; Wang, B.*; Hu, F.*; 加藤 健一*; 服部 高典; et al.

Chemistry of Materials, 35(8), p.3249 - 3255, 2023/04

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

静水圧や化学圧力は、結晶構造を変化させる効率的な刺激であり、材料科学において電気的、磁気的特性のチューニングによく利用されている。しかし、化学圧力は定量化が困難であり、これら両者の定量的な対応関係はまだよくわかっていない。本研究では、負の熱膨張(NTE)を持つ永久磁石の候補である金属間化合物を調べた。放射光X線その場観察により、AlをドープしたHo$$_2$$Fe$$_{17}$$に負の化学圧力があることを明らかにし、単位セル体積の温度・圧力依存性を用いそれを定量的に評価した。また、磁化測定と中性子回折測定を組み合わせることで、磁気秩序に対する化学圧力と静水圧の違いを比較した。興味深いことに、圧力はNTEの抑制と増強を制御するために使用することができた。電子状態計算から、圧力がFermiレベル(EF)に対する主要バンドの上部に影響を与えたことを示しており、これは磁気安定性に影響を与え、それが磁気とNTEを調節する上で重要な役割を果たしていることがわかった。本研究は、圧力の影響を理解し、それを利用して機能性材料の特性を制御する良い例を示している。

論文

Effect of storage environment on hydrogen generation by the reaction of Al with water

Wang, Y.-Q.*; Gai, W.-Z.*; Zhang, X.-Y.*; Pan, H.-Y.*; Cheng, Z.-X.*; 徐 平光; Deng, Z.-Y.*

RSC Advances (Internet), 7(4), p.2103 - 2109, 2017/01

AA2016-0521.pdf:1.55MB

 被引用回数:25 パーセンタイル:64.44(Chemistry, Multidisciplinary)

Al powder was stored in saturated water vapor, oxygen, nitrogen and drying air separately for a time period up to about six months, the degradation behavior of Al activity was characterized by the reaction of Al with water. It was found that water vapor decreased the induction time for the beginning of Al-water reaction and reduced the total hydrogen generation per unit weight of Al, while oxygen increased the induction time and retarded the Al-water reaction. In contrast, the effect of nitrogen and drying air on Al activity was weak. The mechanism analyses indicated that water vapor promoted the hydration of Al surface passive oxide film and speeded up the reaction of Al with water, while oxygen thickened the passive oxide film of Al surface and prolonged its hydration process. These imply that water vapor rather than oxygen is responsible for the degradation of Al activity during storage under ambient condition.

論文

Kinetics study of the Al-water reaction promoted by an ultrasonically prepared Al(OH)$$_{3}$$ suspension

Liang, G.-H.*; Gai, W.-Z.*; Deng, Z.-Y.*; 徐 平光; Cheng, Z.*

RSC Advances (Internet), 6(42), p.35305 - 35314, 2016/04

AA2016-0023.pdf:1.41MB

 被引用回数:16 パーセンタイル:51.51(Chemistry, Multidisciplinary)

Hydrogen is an ideal fuel for fuel cells because its reaction byproduct with oxygen is environmentally benign. To resolve the safe storage and low cost transportation problem, the onsite hydrolysis reaction in water has been recently employed as a new-type portable hydrogen source. Metal Al is thought as a promising hydrogen-generation material due to its relative low price, light atomic weight and abundance in the earth. In order to promote the reaction of Al particles with water and weaken the inhabitation phenomenon of dense passive oxide film on Al surface, the effect of ultrasonically prepared Al(OH)$$_{3}$$ suspension on the kinetics of Al-water reaction was investigated in this paper. It is found that the induction time for the beginning of Al-water reaction decreases and the reaction rate increases with increasing the suspension concentration, volume and temperature, which is ascribed to the exothermic characteristics of Al-water reaction.

論文

Diluted ferromagnetic semiconductor Li(Zn,Mn)P with decoupled charge and spin doping

Deng, Z.*; Zhao, K.*; Gu, B.; Han, W.*; Zhu, J. L.*; Wang, X. C.*; Li, X.*; Liu, Q. Q.*; Yu, R. C.*; 後神 達郎*; et al.

Physical Review B, 88(8), p.081203_1 - 081203_5, 2013/08

 被引用回数:71 パーセンタイル:91.9(Materials Science, Multidisciplinary)

We report the discovery of a diluted magnetic semiconductor, Li(Zn,Mn)P, in which charge and spin are introduced independently via lithium off-stoichiometry and the isovalent substitution of Mn$$^{2+}$$ for Zn$$^{2+}$$, respectively. Isostructural to (Ga,Mn)As, Li(Zn,Mn)P was found to be a ${it p}$-type ferromagnetic semiconductor with excess lithium providing charge doping. First-principles calculations indicate that excess Li is favored to partially occupy the Zn site, leading to hole doping. Ferromagnetism with Curie temperature up to 34 K is achieved while the system still shows semiconducting transport behavior.

論文

Nonlinear simulation of energetic particle modes in JT-60U

Bierwage, A.; 相羽 信行; 篠原 孝司; 藤堂 泰*; Deng, W.*; 石川 正男; 松永 剛; 矢木 雅敏

Proceedings of 24th IAEA Fusion Energy Conference (FEC 2012) (CD-ROM), 8 Pages, 2012/10

Energetic particle mode (EPM) dynamics are simulated using a global nonlinear hybrid code (MEGA). The scenario considered is based on JT-60U shot E039672, just before the onset of a so-called Abrupt Large Event (ALE). The simulation model is gradually extended towards a more realistic representation of the JT-60U plasma, including realistic geometry, realistic pressure, and realistic fast ion distributions. It is found that the mode structure and frequency of the EPM is very robust and can be reproduced by simple models. In contrast, accurate prediction of the growth rate, fluctuation amplitude and fast ion transport may require realistic models. The progress made - in particular, the use of realistic geometry and a realistic fast ion distribution computed by an orbit-following Monte-Carlo code - constitutes an important step forward towards predictive simulations and integrated modelling of energetic particle dynamics in burning plasmas, such as in ITER and DEMO.

論文

Nonlinear simulation of energetic particle modes in high-beta tokamak plasma

Bierwage, A.; 相羽 信行; 藤堂 泰*; Deng, W.*; 石川 正男; 松永 剛; 篠原 孝司; 矢木 雅敏

Plasma and Fusion Research (Internet), 7(Sp.1), p.2403081_1 - 2403081_4, 2012/07

The global hybrid code MEGA is used to study the dynamics of energetic particle modes (EPM) in parameter regimes close to the onset of ideal magnetohydrodynamic (MHD) ballooning instability. This work is motivated by observations of energetic-particle-driven modes in the wall-stabilized regime (so called EWM) in JT-60U, the physics of which have not been fully understood yet. In this study, nonlinear simulations of energetic particle modes (EPM, high frequency, 40-60 kHz) are carried out under conditions, where EWM (low frequency, 1-3 kHz) are observed. Although, EPM are unlikely to interact with EWM directly, the energetic particle transport caused by EPM may affect the total pressure profile and, hence, the stability of kink-ballooning modes, which are thought to be the fundamental modes underlying EWM. The dynamics of EPM near ideal MHD ballooning stability boundary is examined for the first time.

口頭

Nonlinear simulation of energetic particle driven modes in JT-60U

Bierwage, A.; 相羽 信行; Deng, W.*; 石川 正男; 松永 剛; 篠原 孝司; 藤堂 泰*; 矢木 雅敏

no journal, , 

Energetic Particle Modes observed in JT-60U are studied using the global nonlinear code MEGA. For the first time, these modes are simulated in realistic geometry and with realistic bulk plasma pressure. The effect of plasma shaping, bulk pressure and compressibility is examined, looking at the linear growth, initial nonlinear saturation, nonlinear evolution and energetic particle transport. It is found that growth, saturation and evolution of the MHD modes vary significantly depending on the simulation setup. However, the resulting particle transport caused by these strongly driven modes is not correlated to the growth rates and saturation levels. The reduction of the energetic ion density in the central region of the plasma is comparable in all cases studied: circular and shaped plasma, zero and finite bulk beta, weak and strong compressibility effect.

口頭

Effect of annealing models on the welding-induced residual stress and plastic strain in Type 316 stainless steel welded joints

Li, S.; 山口 義仁; 勝山 仁哉; Sun, W.*; Deng, D.*; Li, Y.

no journal, , 

Many flaws due to stress corrosion cracking (SCC) have been reported in the heat affected zone of austenitic stainless steel welded joints in nuclear power plants. High tensile residual stresses and hardness induced by the welding process may affect the initiation and propagation of SCC. During the welding thermal cycles, the accumulated strain hardening can be reduced or eliminated below the melting point due to the dynamic recovery, recrystallization, and grain growth of the material, which is known as the annealing effect. Different annealing models were proposed including the single-stage and two-stage annealing models, which are temperature dependent models to eliminate the accumulated strain hardening in one or two steps, and dynamic annealing models, in which the time-temperature dependent annealing effect can be considered. In this study, numerical investigations were carried out to evaluate the effect of different annealing models on the distributions of welding residual stress and accumulated plastic strain. Two butt-welded joints of Type 316 stainless steel were fabricated. The welding residual stresses of the two welded joints were measured using the neutron diffraction method and sectioning method, respectively. Two-dimensional finite element analysis was performed based on Abaqus platform. Chaboche combined isotropic-kinematic strain hardening model was used. The simulation results of welding residual stresses were compared with measurements. The results obtained have shown that the annealing effect can significantly influence the formation of the accumulated plastic strain and residual stresses in Type 316 stainless steel welded joints. The residual stresses will be overestimated if the annealing effect is neglected, or a relatively high value of the annealing temperature is used. The annealing model plays a major role in determining the magnitude of the accumulated plastic strain in the welding simulation.

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