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. The 2.43 and 2.5 at.% Ni alloys exhibit similar μSR
properties. Both samples are fully magnetic, with average muon local fields
⟨Bloc⟩= 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, at T=0. The
temperature dependence of ⟨Bloc⟩ suggests ordering of
Ni spin clusters rather than isolated spins. Just above TC a two-phase
region is found with 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.Comment: 15 pages, 15 figures, to be published in Phys. Rev.