Low temperature and high pressure magnetization measurements on Ce and U compounds located near quantum critical point

量子临界点附近 Ce 和 U 化合物的低温高压磁化测量

• 批准号: 14540335
• 负责人: NISHIOKA Takashi
• 金额: $ 1.92万
• 依托单位: Nagoya University
• 依托单位国家: 日本
• 项目类别: Grant-in-Aid for Scientific Research (C)
• 财政年份: 2002
• 资助国家: 日本
• 起止时间: 2002 至 2003
• 项目状态: 已结题
• 来源: https://kaken.nii.ac.jp/grant/KAKENHI-PROJECT-14540335/
• 关键词: heavy fermion superconductor; MQT; high pressure and low temperature; magnetization; ferromagnet; UGe_2; 高圧・極低温磁化測定

UGe_2 shows ferromagnetism and superconductivity simultaneously under high pressure and at low temperatures. The ferromagnetic nature had believed to be normal such as Fe, Co and Ni before our present research. The most important fruit in our present work is that ferromagnetic nature of UGe_2 is extremely unusual even at ambient pressure. We have also clarified that the unusual behavior is related to the appearance of superconductivity.The unusual behavior, which we have discovered, is that magnetization jump appears in the ferromagnetic hysteresis curve only below about 1 K. The essential features of the magnetization jump are as follows : (1)the jump occurs at a definite field, i.e., coercive field Hc. (2)Hc increases with decreasing temperature above 1 K, while Hc flattens below about 1 K. (3)Hc is independent of field sweeping rate. These results strongly suggest that the magnetization jump is attributed to macroscopic quantum tunneling.We have examined the relation between the jump and the appearance of the superconductivity. There are two characteristic pressures in UGe_2,i.e., Pc〜l6 kbar and Px〜12 kbar. The ferromagnetism disappears at Pc and an unknown phase transition disappears at Px. The superconducting transition has optimum temperature at around Px, suggesting the important role for superconductivity is the unknown phase transition. We found that the jump only appears below Px, indicating the jump is closely related to the unknown phase transition. These results suggest the jump has an influence on superconductivity.In order to perform these experiments, we developed new static magnetization measurement method. In particular, 'Hall magnetometer' enables us to measure static magnetization very easily at temperatures below 1 K and in pressures up to 10 kbar.

UGe_2在高压和低温下同时表现出铁磁性和超导性。在我们目前的研究之前，铁磁性质被认为是正常的，例如铁、钴和镍。我们目前工作中最重要的成果是，即使在环境压力下，UGe_2 的铁磁性质也是极其不寻常的。我们还澄清了这种异常行为与超导性的出现有关。我们发现的异常行为是在大约1K以下的铁磁磁滞曲线中出现磁化跳跃。磁化跳跃的基本特征如下：（1）跳跃发生在一个确定的场，即矫顽场Hc。 (2)Hc 在 1 K 以上随着温度的降低而增加，而 Hc 在大约 1 K 以下则趋于平缓。 (3)Hc 与场扫描速率无关。这些结果有力地表明磁化跃迁归因于宏观量子隧道效应。我们研究了磁化跃迁与超导性出现之间的关系。 UGe_2中有两个特征压力，即Pc〜l6 kbar和Px〜12 kbar。铁磁性在 Pc 处消失，未知的相变在 Px 处消失。超导转变的最佳温度在 Px 附近，这表明超导的重要作用是未知的相变。我们发现跳跃只出现在Px下方，表明跳跃与未知的相变密切相关。这些结果表明跳跃对超导性有影响。为了进行这些实验，我们开发了新的静态磁化强度测量方法。特别是，“霍尔磁力计”使我们能够在低于 1 K 的温度和高达 10 kbar 的压力下非常轻松地测量静态磁化强度。

项目成果

T.Nishioka, G.Motoyama, S.Nakamura, N.K.Sato: "Nature of Ferromagnetic Phase in Pressure-Induced Ferromagnetic Superconductor UGe_2"Acta Physica Polonica B. 34・3. 485-488 (2003)

T.Nishioka、G.Motoyama、S.Nakamura、N.K.Sato：“压力诱导铁磁超导体 UGe_2 中的铁磁相的性质”Acta Physica Polonica B. 485-488 (2003)

H.Nakane, G.Motoyarna, S.Nakamura, T.Nishioka, N.K.Sato: "Ac magnetic susceptibility measurements on UGe_2"Physica C. (印刷中). (2003)

H.Nakane、G.Motoyarna、S.Nakamura、T.Nishioka、N.K.Sato：“UGe_2 上的 Ac 磁化率测量”Physica C.（出版中）。

Y.Ushida, T.Nishioka, G.Motoyama, S.Nakamura, N.K.Sato: "Thermal expansion measurement under high pressure of UGe2"Physica C. 388-389. 388-389 (2003)

Y.Ushida、T.Nishioka、G.Motoyama、S.Nakamura、N.K.Sato：“UGe2 高压下的热膨胀测量”Physica C. 388-389。

Y.Ushida, H.Nakane, K.Kimura, T.Tsuzuki, T.Nishioka, S.Inoue, K.Matsushita, N.K.Sato: "Construction of a ^3He cryostat using a charcoal sorption pump"Physica C. (印刷中). (2003)

Y.Ushida、H.Nakane、K.Kimura、T.Tsuzuki、T.Nishioka、S.Inoue、K.Matsushita、N.K.Sato：“使用木炭吸附泵构建 ^3He 低温恒温器”Physica C.（出版中） ）（2003）。

T.Nishioka, G.Motoyama, S.Nakamura, H.Kadoya, N.K.Sato: "Unusual Nature of Ferromagnetism Coexisting with Superconductivity in UGe_2"Phys.Rev.Lett.. 88. 237203-1-4 (2002)

T.Nishioka、G.Motoyama、S.Nakamura、H.Kadoya、N.K.Sato：“UGe_2 中铁磁性与超导性共存的异常性质”Phys.Rev.Lett.. 88. 237203-1-4 (2002)