Field-induced local Fermi-liquid states in the underscreened Kondo model for Eu compounds

Abstract

We have studied an underscreened Kondo model for the impurity spin S=7/2S=7/2 capturing the 4f4f characteristics of a nearly divalent Eu ion. By using the numerical renormalization group method, it is shown that an unusual heavy-fermion state is induced from the underscreened spin state when a weak crystal field is introduced. It is also found that the application of the magnetic field enhances the effective mass of the heavy fermions, reflecting the field-induced level crossing of the spin states. We will discuss the mechanism of these mass enhancements in terms of a realization of the two-stage Kondo effect.