Magnetic Properties of Alloys Having Narrow Bands Near the Fermi Level-Impurity Effects and Magnetic Field Effects.

在本研究中，我们研究了以下体系：(1)CeAg和CeB_<6^ >等4f电子化合物，它们的f电子四极矩和它们之间的相互作用对磁性能起主导作用；(2)UPt_3和URu_2Si_2等重电子体系，它们的超导性和磁性有序共存。对于案例(1)，我们首先检查了CeAg_<1- x >In_X。认为四极-四极相互作用是CeAg低温结构相变的主要原因。在CeAg中以In取代Ag，可以认为结构相变的起源是从四极相互作用转变为5d波段John-Teller效应和/或TA_2声子模式的软化。我们还认为，In取代增加了费米能级上的态密度。因此，在CeAg_<1-X>In_X中，结构相变时出现的磁各向异性的大小也有望随着x的增加而变化。为了更清楚地说明这一点，我们在CeAg_<1-X> in_x中，在结构相变温度T_<M^+>附近进行了mu^+SR实验。尽管晶体中存在许多可能的mu^+位点，但我们假设mu^+有2个位点：具有宽的内场分布的位点弛豫时间快，而具有窄场分布的位点弛豫时间慢。对于含有3% In的样品，由于费米能级态密度的增加，与结构相变相关的各向异性降低。结果表明，在T_M处，对mu^+弛豫时间的影响很小，仅观察到沿铁磁有序温度Tc单向减小的临界弛豫。案例(1)的另一个例子是CeB_6。该体系在T= 3,3k和T= 2,3k处分别表现出四极有序和反铁磁有序。通过非线性交流磁化率测量，我们观察到X_2在四极有序温度附近有一个异常。对于情形(2)，我们主要通过用Rh代替Ru来研究杂质对URu_2Si_2的影响。在该体系中，通过控制rh浓度x获得了富相图。详细结果将在几篇论文中发表。少

In the present research, we studied the following systems : (1) 4f-electron compounds such as CeAg and CeB_<6^ﾟ>whose f-electron quadrupole moments and their interactions play dominant role on the magnetic properties (2) heavy electron systems such as UPt_3 and URu_2Si_2 where super conductivity and magnetic ordering coexist each other.For the case (1), we first examined CeAg_<1-X>In_X. It is considered that the quadrupole-quadrupole interactions are responsible for the low temperature structural phase transition in CeAg. By substituting In for Ag in CeAg, the origin of the structural phase transition is considered to change from the quadrupole interactions to 5d-band John-Teller effect and/or softening of the TA_2 phonon mode. It is also considered that the density of state at the Fermi level increases by the In substitution. Thus, magnitude of the magnetic anisotropy appearing upon the structural phase transition is also expected to change with increasing x in CeAg_<1-X>In_X. In orde … More r to clarify this point, we performed the mu^+SR experiment in CeAg_<1-X>In_Xaround the structural phase transition temperature T_<M^+> Althow there are a number of possible mu^+site in the crystal, we analyzed the data assuming 2-sited for mu^+ : the site with a wide internal field distribution that gives a rapid relaxation time, and the site with a narrow field distribution that gives a slow relaxation. For the sample with 3% In, the anisotropy associated with the structural phase transition decreases due to the increase in the density of state at the Fermi level. As the result, the effect on the mu^+ relaxation time is found to be small at T_M, and only the usual critical relaxation that decreases monotorucally towards the ferromagnetc ordering temperature Tc was observed.Another example of the case (1) is CeB_6. This system shows both quadrupole ordering and the antiferromagnetic ordering at T=3, 3K and 2, 3K, respectively. By means of the nonlinear Ac susceptibility measurement, we observed an anomaly in X_2 around the quadrupole ordering temperature.For the case (2), we mainly studied the impurity effect on URu_2Si_2 by substituting Rh for Ru. In this system, a rich phase diagram has been obtained by controlling the Rh-concentration x. Detail of the results will be published soon in several papers. Less