Relaxation of Thermoremanent Magnetization in Different Magnetic Phases Of Fe-rich $\mbox{$\gamma$}$-FeNiCr Alloys

TL;DR

This study investigates the decay of thermoremanent magnetization in Fe-Ni-Cr alloys across different magnetic phases, revealing distinct aging behaviors and confirming theoretical models through experimental measurements.

Contribution

It provides a comprehensive analysis of TRM relaxation in various magnetic phases of Fe-rich alloys, highlighting phase-specific decay behaviors and validating models like Gabay-Toulouse.

Findings

Spin-glass phase shows aging effects with a specific decay form.

Reentrant spin-glass phase fits stretched exponential decay with a constant term.

Ferromagnetic phase exhibits power law decay of TRM.

Abstract

The time decay of the thermoremanent magnetization(TRM) of the $\mbox{Fe}_{80-\mbox{x}}\mbox{Ni}_{\mbox{x}}\mbox{Cr}_{20}$ ($14\leq \mbox{x} \leq 30$) alloys has been measured for four different magnetic phases within the fcc $\mbox{$\gamma$}$-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 $M(t)=M_0(t/t_{w})^{-\gamma}\exp[-(t/\tau)^{1-n}]$ 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 T$_{\mbox{c}}$ and a local maximum just above T$_{\mbox{c}}$. 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).