The effect of the crystal electric field on the Kondo-type fluctuations in

Abstract

We present a positive-muon spectroscopy study of the cubic Kondo lattice , where the crystal-field splittings of the ion amount to a few tens of K. The transition from the paramagnetic to the antiferromagnetic state is detected at . The zero-field data provide evidence of an unusual temperature dependence of the mean nuclear dipole field at the muon site. The longitudinal relaxation rate as well as the published quasi-elastic neutron linewidth, both recorded far into the paramagnetic region (, are analysed in detail. We show that the classical kf exchange interaction cannot explain the observed thermal variation of the dynamical and neutron widths. We perform a calculation of the 4f excitation spectra using the expansion, applied to the Anderson one-impurity Hamiltonian in the non-crossing approximation (NCA), in the presence of crystal-field splittings, and compare the results with the observed thermal variations of the dynamical widths. Whereas the NCA reasonably explains the neutron measurements, it strongly overestimates the low-temperature width. We discuss different possible reasons for this discrepancy.