Resistance Anomalies Accompanying Crossover from Heavy-Fermion Regime to Intermediate-Valence Regime: A Study of Cu–Ni Substitution and Pressure Effects on CeCu₂Si₂

Abstract

We present detailed investigations on the effects of Ni substitution (x) on Ce(Cu 1¹x Ni x ) 2 Si 2 with x < 0.3, and a pressure ( p) study for x = 0.04(2), 0.05(2), and 0.09(2) by resistivity measurements. The Cu-Ni substitution suppresses both antiferromagnetic fluctuations and superconductivity in CeCu 2 Si 2 , and leads to a dramatic crossover from the heavy-fermion (HF) regime to the intermediate-valence (IV) regime with progressive Ni doping. The crossover can be characterized by a marked increase in Kondo temperature evaluated from resistivity, specific heat, and susceptibility measurements. In high-pressure resistivity measurements, the Ni-doped system exhibits similar anomalies to those observed in CeCu 2 Si 2 , namely, T-linear dependence, an enhancement of residual resistivity, and a marked decrease in the A coefficient of the T 2 -resistivity. Furthermore, we observed an unexpected upturn anomaly in resistivity in the Ni-doped system under high pressure. By constructing the x-p phase diagram of Ce(Cu 1¹x Ni x ) 2 Si 2 , we demonstrate that the crossover from the HF regime to the IV regime can be associated with these characteristic anomalies in resistivity.

Time-Temperature Dependent Short- and Long-Range Structural Transformation in Medium-Entropy Alloys

“…In such a partially ordered/disordered solid solution, the formation of a characteristic topological and compositional short-/middlerange structure is expected, and the relationship between the local structures and material properties is of subsequent natural interest. For example, it is interesting to note whether there is an additional mechanism in addition to precipitation hardening, what novel transport properties emerge, the similarity in the T-linear resistivity behavior between a compositionally disordered system CrCoNi 21) and intermediate valence systems, 22,23) and the detail of the cocktail effect on local structures. 16) The possible structural models are also displayed.…”