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NMR Study of Magnetic Property in Heavy Fermion Superconductor CeCu_2Si_2

重费米子超导体CeCu_2Si_2磁性能的NMR研究

基本信息

批准号：
03452041
负责人：
KITAOKA Yoshio
金额：
$ 3.78万
依托单位：
Osaka University
依托单位国家：
日本
项目类别：
Grant-in-Aid for General Scientific Research (B)
财政年份：
1991
资助国家：
日本
起止时间：
1991 至 1992
项目状态：
已结题

来源：
https://kaken.nii.ac.jp/en/grant/KAKENHI-PROJECT-03452041/
关键词：
Heavy Fermion Superconductivity Magnetic Transition CeCu_2Si_2 NMR NQR

项目摘要

The magnetic correlation in the heavy fermion superconductor, CeCu<@D22.02@>D2Si<@D22@>D2 and Th-doped Ce<@D21-x@>D2Th<@D2x@>D2Cu<@D22.2@>D2Si<@D22@>D2, has been investigated by Cu nuclear magnetic resonance (NMR) and nuclear quadrupoleresonance (NQR). For CeCu<@D22.02@>D2Si<@D22@>D2 with T<@D2c@>D2 = 0.72KJ, a "magnetic transition" has been found at around 0.8 K in applied fields up to 3.5T. Below the transition temperature, Cu NMR loses the intensity suddenly without any broadening and shift of the spectrum, and the spin-echo decay rate, 1/T<@D22@>D2, at H = 13.3kOe, increases with decreasing temperature, which is different from the behavior expected in a static magnetically ordered state. The "magnetic transition" just above T<@D2c@>D2 is quite unusual in a sense that the ordered state may not be in a completely static regime, but possesses some dynamic aspect. We have constructed a magnetic phase diagram in the field-temperature plane for CeCu<@D22.02@>D2Si<@D22@>D2. To ensure the magnetic instability in CeCu<@D22@>D2 we have investigated a magnetic and superconducting phase diagram of Th-doped Ce<@D21-x@>D2Th<@D2x@>D2Cu<@D22.2@>D2Si<@D22@>D2. Static magnetic ordering with T<@D2n@>D2 = 2.4K and 4.5K for x=0.08 and 0.12, respectively, is evidenced by a pronounced broadening of the <@D163@>D1Cu-NQR and -NMR spectra and a mean-field type of anomaly in the specific heat. In contrast, for the lightly Th-doped compounds with x (] SY.ltoreq.[) 0.064, there has been observed neither any signature of a broadening of the NQR and NMR spectra nor an anomaly of the specific heat, but a dramatic reduction of the NMR and NQR intensities below a temperature ranging from 0.9 K to 1.3 K upon increasing Th-content. It is emphasized that the unusual "magnetic transition" found in undoped and lightly Th-doped CeCu<@D22.2@>D2Si<@D22@>D2 should be distinguished from the static magnetic ordering in the heavily Th-doped systems.

用Cu核磁共振（NMR）和核四极共振（NQR）研究了重费米子超导体CeCu<@D22.02 @> D2 Si <@D22@>D2和掺Th的Ce<@D21-x@> D2 Th <@D2x@>D2Cu<@D22.2@> D2 Si <@D22@>D2的磁关联.对于T<@D2c@>D2 = 0.72KJ的CeCu<@D22.02 @> D2 Si <@D22@>D2，在0.8K附近，外加磁场高达3.5T时，发现了一个“磁转变”。在转变温度以下，CuNMR谱线没有任何展宽和位移，但强度突然减弱，自旋回波衰减速率（1/T<@D22@>D2，H = 13.3kOe）随温度的降低而增加，这与静态磁有序态的预期行为不同。在T<@D2c@>D2之上的“磁转变”是非常不寻常的，在某种意义上，有序状态可能不是完全静态的，而是具有一些动态方面。我们绘制了CeCu<@D22.02@> D2 Si <@D22@>D2的场温平面磁相图。为了确定CeCu<@D22@>D2的磁不稳定性，我们研究了Th掺杂的Ce<@D21-x@> D2 Th <@D2x@>D2Cu<@D22.2@> D2 Si <@D22@>D2的磁和超导相图。<@D163@>D1Cu-NQR和-NMR谱的明显展宽和比热的平均场型异常证明了静态磁有序性（T<@D2n@>D2 = 2.4K和4.5K（x=0.08和0.12））。相比之下，对于x（] SY ≤ 0. 0.064，既没有观察到NQR和NMR谱的加宽的任何特征，也没有观察到比热的异常，但是当增加Th含量时，NMR和NQR强度在0.9 K至1.3 K范围内的温度以下急剧降低。强调了在未掺杂和轻掺Th的CeCu<@D22.2@> D_2Si <@D22@> D_2中发现的异常“磁转变”应与重掺Th系统中的静态磁有序区别开来。