Ferromagnetic quantum criticality in the alloy CePd1-xRhx

Abstract

The CePd1−xRhx alloy exhibits a continuous evolution from ferromagnetism (TC=6.5K) at x=0 to a mixed-valence (MV) state at x=1. We have performed a detailed investigation on the suppression of the ferromagnetic (F) phase in this alloy using dc (χdc) and ac (χac) susceptibility, specific heat (Cm), resistivity (ρ), and thermal expansion (β) techniques. Our results show a continuous decrease of TC(x) with negative curvature down to TC=3K at x∗=0.65, where a positive curvature takes over. Beyond x∗, a cusp in χac is traced down to T∗C=25mK at x=0.87, locating the critical concentration between x=0.87 and 0.90. The quantum criticality of this region is recognized by the −log(T∕T0) dependence of Cm∕T, which transforms into a T−q (q≈0.5) one at x=0.87. At high temperature, this system shows the onset of valence instability revealed by a deviation from Vegard’s law (at xV≈0.75) and increasing hybridization effects on high-temperature χdc and ρ(T). Coincidentally, a Fermi liquid contribution to the specific heat (γ) arises from the MV component, which becomes dominant at the CeRh limit. In contrast to antiferromagnetic systems, no Cm∕T flattening is observed for x>xcr but, rather, the mentioned power-law divergence, which coincides with a change of sign of β(T). The coexistence of F and MV components and the sudden changes in the T dependencies are discussed in the context of randomly distributed magnetic and Kondo couplings.