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.

What does the muon spin-relaxation rate measure in 4f paramagnets with strong crystal fields and weak inter-site correlations?

“…It is to be emphasized that this model calculation does not apply in the actual case of YbAuCu 4 because of the presence of the Kondo coupling. The thermal variation of Q in YbAuCu 4 shows a downward curvature [16], and that of µSR is detailed in [2]. A tentative interpretation of these data within a Kondo model is given in [2].…”

“…The thermal variation of Q in YbAuCu 4 shows a downward curvature [16], and that of µSR is detailed in [2]. A tentative interpretation of these data within a Kondo model is given in [2].…”

“…This describes compounds with magnetic ions located in sites of cubic symmetry. The result derived below has been used to analyse µSR data recorded for the Kondo lattice compound YbAuCu 4 [2]. As mentioned in the previous section, in cubic symmetry, ˜ αβ is proportional to the on-site symmetrized spin correlation function ˜ :…”

“…The NCA calculation of [12] has been performed without taking account of the CEF splittings. The extension to the CEF case will be given in [2]. In this respect, it should be emphasized that the Kondo temperature is renormalized by the presence of the CEF splittings.…”

“…The purpose of this paper is to provide such a framework and to give examples of its use by analysing recently published µSR data in the strongly correlated electron systems CeNiSn and CePt 2 Sn 2 . In a separate work we use this framework to analyse µSR data in the Yb-based weak Kondo lattice YbAuCu 4 [2].…”