MCD study on Ce_xLa_1-xNi: Difference between the "local" and "coherent" Kondo effect

Temperature dependence of Ce 4f magnetic moment was measured on Ce _xLa_1-xNi (x = 1.0, 0.9, 0.8, 0.7, 0.4) using the 3d-4f core excitation magnetic circular dichroism (MCD). The bulk magnetic susceptibilities of these samples were also measured with SQUID. The two results were largely different at temperatures lower than "coherent Kondo temperature", T_K. The MCD results showed the Curie-Weiss behavior but the estimated negative Weiss temperatures are remarkably lower than T_K, except the case of x = 0.4 showing a positive Weiss temperature but not exhibiting the Kondo effect. It is suggested that the MCD results reflect a local spin-singlet effect with smaller binding energy, while the bulk Kondo temperatures are raised due to coherent hybridization between 4f and ligand states.