Non-equilibrium magnetic response in concentrated spin-glass AuFe(11%) alloy

TL;DR

This study investigates the non-equilibrium magnetic behavior of AuFe(11%) alloy, revealing complex spin-glass dynamics, memory effects, and a nontrivial energy landscape through detailed magnetization and susceptibility measurements.

Contribution

It provides experimental evidence that the field-cooled state in AuFe(11%) alloy is a non-equilibrium, nontrivial energy landscape, challenging mean-field theories of spin-glass equilibrium states.

Findings

Peak in ZFC and FC magnetization at Tf = 33 K indicating spin freezing

Frequency-dependent shift of susceptibility cusp at Tf

Memory effects in the FC state confirming non-equilibrium behavior

Abstract

We report a detailed study of dc magnetization and ac susceptibility performed on the zero field cooled (ZFC) and field cooled (FC) state of polycrystalline AuFe(11%) alloy. The temperature variation of ZFC and FC dc magnetization at low fields show a distinct peak around Tf = 33 K, which indicates the cooperative freezing of the finite size spin clusters. A weak thermomagnetic irreversibility between ZFC and FC magnetization appears at a temperature Tir, which is slightly below Tf. The ZFC ac susceptibility shows a sharp cusp at Tf, which shifts towards higher temperatures with an increase in the frequency of the ac magnetic field. When ac susceptibility is recorded after cooling the sample from high temperature in the presence of dc bias magnetic field, the susceptibility cusp gets broadened. In this case, no perceptible frequency dependency of the Tf has been observed, but a significant dispersion in the ac susceptibility is present below Tf. This clearly indicates the non-equilibrium nature of the FC state.In addition, the FC state of AuFe(11%) alloy exhibits a pronounced memory effect which further underlines that the FC state is not an equilibrium state. In contrast to the general perception obtained through the meanfield theories of thermodynamic phase transition in spin-glass envisaging the FC state to be an equilibrium state, the present experimental results clearly indicate that the energy landscape of the FC state of AuFe(11%) alloy is a nontrivial one