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論文

Colossal negative thermal expansion induced by magnetic phase competition on frustrated lattices in Laves phase compound (Hf,Ta)Fe$$_2$$

Li, B.; Luo, X. H.*; Wang, H.*; Ren, W. J.*; Yano, S.*; Wang, C.-W.*; Gardner, J. S.*; Liss, K.-D.*; Miao, P.*; Lee, S.-H.*; et al.

Physical Review B, 93(22), p.224405_1 - 224405_6, 2016/06

 被引用回数:45 パーセンタイル:85.49(Materials Science, Multidisciplinary)

Competition between ferromagnetic and antiferromagnetic phases on frustrated lattices in hexagonal Laves phase compound Hf$$_{0.86}$$Ta$$_{0.14}$$Fe$$_2$$ is investigated by using neutron diffraction as a function of temperature and magnetic fields and density-functional-theory calculations. At 325 K, the compound orders into the 120$$^{circ}$$ frustrated antiferromagnetic state with well-reduced magnetic moment and an in-plane lattice contraction simultaneously sets in. With further cooling down, however, the accumulated distortion in turn destabilizes this susceptible frustrated structure. The frustration is completely relieved at 255 K when the first-order transition to the ferromagnetic state takes place, where a colossal negative volumetric thermal expansion, $$-123 times 10^{-6}$$/K, is obtained. Meanwhile, the antiferromagnetic state can be suppressed by few Tesla magnetic fields, which results in a colossal positive magnetostriction. Such delicate competition is attributed to the giant magnetic fluctuation inherent in the frustrated antiferromagnetic state. Therefore, the magnetoelastic instability is approached even under a small perturbation.

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

 被引用回数:8 パーセンタイル:36.17(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

Wideband low-output-impedance RF system for the second harmonic cavity in the ISIS synchrotron

入江 吉郎; Dooling, J.*; Horan, D.*; Kustom, R.*; Middendorf, M.*; Pile, G.*; Bayley, D.*; Cross, G.*; Gardner, I.*; Glover, M.*; et al.

Proceedings of 10th European Particle Accelerator Conference (EPAC 2006) (CD-ROM), p.321 - 323, 2006/00

広帯域で低出力インピーダンス第2高調波空洞が日米英の3か国協力により開発された。低出力インピーダンスの特性は、陽極からグリッド電極へのフィードバックループにより実現される。30オーム以下の出力インピーダンスをもつこのシステムは、周波数2.7$$sim$$6.2メガヘルツ,繰返し周波数50ヘルツの条件で大電力試験を行い、安定した高電圧発生(加速間隙あたり12キロボルト)に成功した。英国ラザフォード研究所のISISシンクロトロンにこの装置を適用した場合、精度良いビーム平坦化が可能となり空間電荷力が緩和される。その結果、大強度陽子シンクロトロンにおけるビーム損失の低減に大いに役立つことが期待される。

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