Magnetism of Pd1-xNix alloys near the critical concentration for ferromagnetism

Abstract

We report results of a muon spin rotation and relaxation (μSR) study of dilute Pd1-xNix alloys, with emphasis on Ni concentrations x=0.0243 and 0.025. These are close to the critical value xcr for the onset of ferromagnetic long-range order (LRO), which is a candidate for a quantum critical point. Additional control data were taken for pure nonmagnetic Pd, and for an alloy where ferromagnetism is well established (x=0.05). The 2.43 and 2.5 at.% Ni alloys exhibit similar μSR properties. Both samples are fully magnetic, with average zero-temperature muon local fields 〈Bloc(T=0) âŒ=2.0 and 3.8 mT and Curie temperatures TC=1.0 and 2.03 K for 2.43 and 2.5 at.% Ni, respectively. The temperature dependence of 〈Bloc⌠suggests ordering of Ni spin clusters rather than isolated spins. Just above TC, the temperature where LRO vanishes, a two-phase region is found with coexisting separate volume fractions of quasistatic short-range order (SRO) and paramagnetism. The SRO fraction decreases to zero with increasing temperature a few kelvin above TC. This mixture of SRO and paramagnetism is consistent with the notion of an inhomogeneous alloy with Ni clustering. The measured values of TC extrapolate to xcr=0.0236±0.0027. The dynamic muon spin relaxation in the vicinity of TC differs for the two samples: a relaxation-rate maximum at TC is observed for x=0.0243, reminiscent of critical slowing down, whereas for x=0.025 no dynamic relaxation is observed within the μSR time window. The data suggest a mean-field-like transition in this alloy. © 2014 American Physical Society.