Relaxation of Thermoremanent Magnetization in Different Magnetic Phases Of Fe-rich γ-FeNiCr Alloys

The time decay of the thermoremanent 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) −γ exp[−(t/τ)] for the entire time domain. In the reentrant 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). PACS Number : 75.30.Kz, 75.50.Bb, 75.50.Ee, 75.50.Lk Typeset using REVTEX