SPIN FLUCTUATIONS IN URANIUM COMPOUNDS

(1)稀铀杂质体系：采用两种晶格参数不同的非磁性基质，研究了U离子在稀UAl_2和U_2ZN_(17)&gt_(17)中的单位性质，其对应的致密化合物表现出非常相反的磁性行为。在所有的情况下，观察到的行为都可以用晶场下的近藤效应来半定量地解释。但与Ce基4f系统不同的是，致密的5f化合物的行为不能简单地描述为相应基质中U杂质的聚集。(2)U化合物自旋动力学的系统学：反铁磁性的U_3Pd_t；20&Gt；Si_6(T_N=19K)是一个典型的局域5f力矩系统。在核磁共振测量中，我们发现核纵向弛豫时间T_1随着T的增加几乎呈线性增加，这表明低能自旋动力学也可以从核磁共振的角度用局域5f矩来理解，但5f矩强烈依赖于T的大驰豫速率表明，在顺磁状态下，5f和传导电子的杂化导致的单位动力学主导着低能自旋动力学。观察到的行为与UP、UAS和U3P4等有序温度较高的U化合物有许多相似之处，被认为是磁有序U系统的共同特征，接近局域力矩极限。(3)U化合物的多Q磁结构：我们在4.2K的磁有序双Q型IA态的核磁共振谱中发现了^&lt；75&gt；的精细结构。这些结构很可能与多Q结构有关，可以作为双Q态四极有序的证据。

(1) Dilute U Impurity Systems : Single-site properties of U ions have been investigated in dilute UAI_2 and U_2Zn_<17>, with counterpart dense compounds showing quite contrasting magnetic behavior, by using respectively two different non-magnetc matrices with significantly different lattice parameters. In all the cases, the observed behavior can be explained semi-quantitatively in terms of Kondo effect under crystal field. But differently from Ce-based 4f systems, the behavior of the dense 5f compounds cannot be described as simple collection of the U impurities in the corresponding matrices. Moreover, the variation of the characteristic energy-scale of the system is not at all monotonous against that in the lattice parameters.(2) Systematics of the Spin Dynamics of U Compounds : The antiferromagnetic U_3Pd_<20>Si_6 (T_N=19 K) was previously characterized as a typical localized 5f moment system. In NMR measurements, we have found that the nuclear longitudinal relaxation time T_1 increases almost linearly with T above about 30 K. This indicates that the low-energy spin dynamics can be understood in terms of localized 5f moment also from the NMR viewpoint, but a strongly T-dependent, large relaxation rate of the 5f moment shows that single-site dynamics due to hybridization between 5f and conduction electrons dominate the low-energy spin dynamics in the paramagnetic state. The observed behavior has many similarities to those on U compounds with relatively high ordering temperatures such as UP, UAs and U_3P_4, and are considered as common characteristics in magnetically ordering U systems that are close to the localized moment limit.(3) Multi-Q Magnetic Structure of U Compounds : We have found fine structures in the ^<75>As NMR spectrum at 4.2 K in the magnetically ordered double-Q type IA state. These structures are very likely to be related to the multi-Q structure, and can be an evidence for the quadrupole order in the double-Q state.