Effects of random fields on the reversal of magnetisation of Ising ferromagnet

TL;DR

This study investigates how quenched random fields influence magnetisation reversal times in a 2D Ising ferromagnet, revealing that random fields generally decrease reversal times and affect nucleation processes, with implications for understanding magnetic systems.

Contribution

It provides a detailed analysis of the effects of different random field distributions on reversal times and nucleation, extending the classical theory with new simulation insights.

Findings

Reversal time decreases with random fields of any distribution.

Metastable volume follows Avrami's law.

Large random field widths inhibit single droplet nucleation.

Abstract

We have studied the reversal time of the magnetisation in two dimensional Ising ferromagnet in the presence of externally applied uniform magnetic field using Monte Carlo simulation based on Metropolis single spin flip algorithm. Then we have investigated the change in reversal time due to the presence of quenched random field in addition to the uniform magnetic field. We report the results of statistical distribution of reversal times in the presence of three different types of the distributions (namely, uniform, bimodal and normal) of random fields and compared the results with those obtained for uniform field only. We have observed that the reversal time decreases due to the presence of any kind (of distribution) of the random fields. The metastable volume fraction is observed to follow the Avrami's law. Dependence of reversal times on temperature and different widths of the distributions of random fields are also reported. We have also checked whether the system obeyed Becker-Doring theory of classical nucleation in presence of additional random field and tried to investigate the range of the width of the distribution of random field. For larger width of the distribution of random field, the system fails to show the reversal via the nucleation of a single droplet (for small values of uniform field only). The possible reason is analysed.