Anomalous paramagnetic-state μSR in spin-glass AgMn

Abstract

Muon spin rotation (μSR) experiments have been carried out in the paramagnetic state (T≳T_g) of a dilute AgMn spin glass, to probe internal field distributions during the onset of impurity‐spin freezing. μ⁺ resonance frequencies and depolarization rates were measured in a 1.6 at.% Mn sample in transverse fields between 0.15 and 5 kOe for temperatures up to ∼3T_g. The depolarization rate Λ increased well above the value Λ_d expected in the absence of impurity‐spin exchange coupling as T_g was approached from above. The largest relative increase of Λ was obtained for lowest fields. The average precession frequency was constant to within 0.2% down to 1.1T_g. The data scale roughly with T/T_g and H/T_g when compared to recent μSR studies of CuMn. Although a case has been made for attributing this anomamous increase in Λ to dynamic broadening (spin‐lattice relaxation), evidence exists which argues that static inhomogeneity in the muon hyperfine field is the origin of Λ. If this is the case, the absence of muon environments with weak hyperfine couplings conflicts with the notion that clustering or percolative effects are involved in the spin‐glass transition. The μSR results may be relevant to recent interpretations of ESR data.