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

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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