Relaxation of thermo-remanent magnetization in different magnetic phases of Fe-rich γ-FeNiCr alloys

Abstract

The time decay of the thermo-remanent magnetization (TRM) of the Fe80−xNixCr20 (14 ≤ x ≤ 30) alloys has been measured for four different magnetic phases within the fcc γ-phase using a SQUID magnetometer. In the spin-glass phase (SG) (x = 19) very distinct ageing effects are observed where M(t) can be described as M(t) = M0(t/tw)−γexp[−(t/τ)1−n] for the entire time domain. In the re-entrant spin-glass (RSG) (x = 23 and 26), M(t) can be better represented by the stretched exponential with an addition of a constant term which can be well explained by the Gabay-Toulouse (GT) model. We have also measured the linear and non-linear ac susceptibilities for the sample x = 23 and confirmed the presence of the ferromagnetic (FM) ordering down to the lowest temperature. In the RSG (x = 23), the TRM shows a minimum near Tc and a local maximum just above Tc. In the FM phase (x = 30), the popular prediction of the power law decay of the TRM is observed. The latter is indistinguishable from the stretched exponential in the antiferromagnetic (AF) phase (x = 14).