Spin-glass instability of short-range spherical ferromagnet

TL;DR

This paper uses a spherical model to analyze how weak disorder can induce a spin-glass phase in short-range ferromagnets, predicting specific magnetic behaviors near the transition.

Contribution

It introduces a spherical model with short-range ferromagnetic and weak frustrated interactions to describe spin-glass transition in disordered ferromagnets, highlighting new thermodynamic features.

Findings

Spin-glass phase replaces ferromagnetic phase at any disorder level.

Longitudinal susceptibility becomes constant below transition.

Third order nonlinear susceptibility exhibits temperature oscillations.

Abstract

In structurally disordered ferromagnets the weak random dipole-dipole exchange may transform the polydomain state into a spin-glass one. To some extent the properties of such phase in disordered isotropic ferromagnet can be qualitatively described by the spherical model with the short-range ferromagnetic interaction and weak frustrated infinite-range random-bond exchange. This model is shown to predict that spin-glass phase substitute the ferromagnetic one at the arbitrary small disorder strength and that its thermodynamics has some similarity to that of polydomain state along with some significant distinctions. In particular, the longitudinal susceptibility at small fields becomes frozen below transition point at a constant value depending on the disorder strength, while the third order nonlinear magnetic susceptibilitiy exhibits the temperature oscillations in small field near the transition point. The relation of these predictions to the experimental data for some disordered isotropic ferromagnets is discussed.