Crystalline electric field and Kondo energy scales in YbCu 5− xAg x

Abstract

The specific heat of LuCu 5− x Ag x reference samples was measured to reanalyse the heavy-fermion behaviour of the isostructural AuBe 5-type cubic system YbCu 5− x Ag x with x=0–1 which is a series of dense Kondo compounds whose characteristic temperature T 0 decreases as x decreases. For YbCu 5− x Ag x , the γ-value increases from 210 mJ/ mol K 2 for x=1.0 to 550 mJ/ mol K 2 for x=0.0. The analysis of the magnetic susceptibility and of the magnetic contribution to the specific heat in terms of Coqblin–Schrieffer (CS) model reveals a significant reduction of the effective ground state degeneracy: While YbCu 4Ag is well described by the CS model with J= 7 2 and T 0=150 K , one has to consider a crystalline electric field splitting of the Yb 3+ ground state multiplet with an energy scale of the order of 80 K and a Kondo contribution corresponding to the CS model with J= 3 2 and T 0∼30 K in the case of YbCu 5, i.e. there is a cross-over of the characteristic energy scales of the Kondo interaction and of the CEF splitting within the series Yb(Cu,Ag) 5.