Nonmonotonous evolution of the Kondo temperature in the phase diagram of Ce(Pd1-xCux)(2)Si-2

Abstract

The evolution of the behavior of the Ce 4f electron with the Cu content in the alloy Ce(Pd1−xCux)2Si2 was investigated by determining its structural, magnetic, transport, and thermal properties. Results obtained on 15 samples with compositions distributed along the whole concentration range allow us to draw a magnetic phase diagram showing three distinct regions. The first region at low Cu concentrations corresponds to the antiferromagnetic-ordered regime. The fast suppression of this magnetic order between x=0.2 and x=0.25 suggests the presence of a critical point which separates this region from the second one at larger x values where no magnetic order is observed. The main characteristic of this second region, which extends up to x=0.7, is a pronounced increase of the Kondo temperature TK, from TK≈15 K at x=0.25 to TK≈50 K at x=0.7. This is in contrast with the fast decrease of TK in the region with x>0.7. In this region a small anomaly with a ferromagnetic character is observed in the specific heat arround 4 K. The change in the evolution of TK with x coincides with a change in the composition dependence of the c lattice parameter of the tetragonal structure, pointing to a structure-related origin of this unusual TK(x) behavior. This nonmonotonous TK(x) dependence is reproduced using local-density-approximation band-structure calculations, which show a maximum of the hybridization strength between conduction electrons and Ce 4f states for intermediate Cu concentrations. Such a TK(x) dependence which contradicts the monotonous dependence observed in all other Ce-based alloy systems is the hallmark of the Ce(Pd1−xCux)2Si2 alloy, which cannot be described as a Fermi-liquid system in the nonmagnetic region.