Theoretical studies on switching of magnetisation in thin film

Moumita Naskar, Muktish Acharyya

Published 2022-08-06Version 1

In the present chapter, we focus on the switching of magnetisation or the metastable lifetime of a ferromagnetic system. In this regard, particularly the Ising model and the Blume-Capel model have been simulated in presence of an externally applied magnetic field by Monte-Carlo simulation technique based on Metropolis algorithm. Magnetisation switching is found to be faster in presence of disorder modeled here by a quenched random field. The strength of the random field is observed to play a similar role as played by temperature. Becker-D\"oring theory of classical nucleation (originally proposed for the spin-1/2 Ising system) has been verified in the random field Ising model. However, stronger random field affects the nucleation regime. In a cubic Ising lattice, surface reversal time is found to be different from the bulk reversal time. That distinct behaviour of the surface in contrast to the bulk has been studied here by introducing a relative interfacial interaction strength ($R$). Depending on $R$, temperature and applied field, a competitive switching of magnetisation of surface and bulk is noticed. The effect of anisotropy ($D$) on the metastable lifetime has been investigated. We report a linear dependency of the mean macroscopic reversal time on a suitably defined microscopic reversal time. The saturated magnetisation $M_f$, after the reversal, is noticed to be strongly dependent on $D$. That $M_f$, $D$, and $h$ (field) are found to follow a proposed scaling relation. Finally, Becker-D\"oring theory as well as Avrami's law are verified in spin-$s$ Ising and Blume-Capel models. The switching time depends on the number of accessible spin states also.