NMR Study of Magnetic Property in Heavy Fermion Superconductor CeCu_2Si_2

用铜核磁共振和核四极共振研究了重费米子超导体Cecu&lt；@D22.02@&gt；D2Si&lt；@D22@&gt；D2和Th掺杂Ce&lt；@D21-x@&gt；D2Th&lt；@D2x@&gt；D2Cu&lt；@D22.2@&gt；D2Si&lt；@D22@&gt；D2，中的磁关联。对于具有T&lt；@D2C@&gt；D2=0.72KJ的Cecu&lt；@D22.02@&gt；D2Si&lt；@D22@&gt；D2，在直到3.5T的外加磁场中发现了约0.8K的“磁相变”。在相变温度以下，铜核磁共振突然失去强度，光谱没有任何展宽和移动，在H=13.3kOe时，自旋回波衰减率1/T&lt；@d22@&gt；d2随着温度的降低而增加，这与静态磁序状态下的行为不同。T&lt；@D2c@&gt；D2上方的“磁跃迁”在某种意义上是非常不寻常的，因为有序状态可能不是完全静态的，而是具有一些动态方面的。我们建立了Cecu&lt；@D22.02@&gt；D2Si&lt；@D22@&gt；D2在场温平面上的磁相图。为了保证Cecu&lt；@D22@&gt；D2的磁不稳定性，我们研究了Th掺杂Ce&lt；@D21-x@&gt；D2Th&lt；@D2x@&gt；D2Cu&lt；@D22.2@&gt；D2Si&lt；@D22@&gt；D2.的磁相图和超导相图当x=0.08和0.12时，T&lt；@D2n@&gt；D2分别为2.4K和4.5K的静磁有序化的证据是&lt；@D163@&gt；D1Cu-NQR和-核磁共振谱的显著展宽和比热的平均场型反常。相反，对于x()=0.064的轻度Th掺杂的化合物，没有观察到核磁共振和核磁共振谱的展宽和比热的异常，但随着Th-含量的增加，核磁共振和核磁共振的强度在0.9K到1.3K的温度范围内急剧下降。强调指出，在未掺杂和轻掺Th的CeCu&lt；@D22.2@&gt；D2Si&lt；@D22@&gt；D2中发现的反常“磁相变”应与重掺Th的静态磁有序相区别。

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.