Study on Nuclear Spin Order and Quantum Fluctuation in Pt metal

为了估计富集195 Pt金属中的核自旋有序温度，对富集195 Pt金属细线样品进行NMR测量。由NMR测量得到了自旋-晶格弛豫时间（T_1）和自旋-自旋弛豫时间（T_2）随温度和场的变化关系。在富集195 Pt金属中也测量了Knight位移值。这些测量也对含有33.8%195Pt的天然Pt金属细线进行。T_1和Knight位移的实验结果在两个试样中是相同的。富集样品的T_2约为天然样品的一半。这可以通过富集样品中的核自旋之间的较短距离来理解，从而导致更强的自旋-自旋相互作用。但是非常有趣的结果是T_2的场依赖性。我们观察到富集样品中T_2的场依赖性比天然Pt样品中的大四倍。用SQUID磁强计测量了富集195 Pt样品的磁化强度随温度的变化。它表现出相当大的Curi-Weiss温度依赖性。在80%富集的195 Pt细线样品和用同样方法制备的天然Pt细线样品中也观察到类似的磁化强度随温度的变化。磁化强度的大小与195 Pt核自旋的数量成正比。居里温度为0.7K。用普通方法制作的天然Pt金属细线，没有表现出这种大的磁化强度的温度依赖性。我们将研究这种异常的磁性行为在铂金属的起源。

To estimate a nuclear spin ordering temperature in enriched 195Pt metal, NMR measurements were perfonned for the enriched 195Pt metal thin wire specimen. From the NMR measurements, the temperature and field dependences of spin-lattice (T_1) and spin-spin relaxation times(T_2) were obtained. The value of Knight shift was also measured in enriched 195Pt metal. These measurements were also performed for the natural Pt metal thin wire which contains 33.8% 195Pt. Experimental results of the T_1 and Knight shift are same in both specimens. The T_2 in enriched sample is half of that in natural Pt specimen. This can be understood by the shorter distance among the nuclear spins in the enriched sample, resulting the stronger spin-spin interaction. But very interesting result is the field dependence of the T_2. We observed the four times larger field dependence of T_2 in the enriched sample than one in the natural Pt sample. At present we cannot explain this result.The temperature dependence of the magnetization of the enriched 195Pt sample was measured by using a SQUID magnetometer. It shows rather large Curi-Weiss like temperature dependence. The similar temperature dependences of the magnetization were also observed in the 80% enriched l95Pt thin wire sample and also the natural Pt thin wire sample which was made by the same procedures as the enriched thin wire sample. The amount of the magnetization is proportional the number of the 195Pt nuclear spin. Curie-temperature was estimated to be 0.7K. The natural Pt metal thin wire made vy the ordinary method, did not show this large temperature dependence of the magnetization. We will investigate, the origin of this anomalous magnetic behavior in Pt metal.