Kinetic Ising Systems as Models of Magnetization Switching in Submicron Ferromagnets

TL;DR

This paper uses Monte Carlo simulations of kinetic Ising models to understand magnetization switching in sub-micron ferromagnets, aligning theoretical predictions with recent experimental observations.

Contribution

It demonstrates that droplet theory accurately predicts magnetization dynamics in simulated sub-micron ferromagnets, linking theory with experimental MFM data.

Findings

Simulations agree with droplet theory predictions.

Switching involves local nucleation and droplet growth.

Qualitative match with experimental magnetization switching.

Abstract

Recently experimental techniques, such as magnetic force microscopy (MFM), have enabled the magnetic state of individual sub-micron particles to be resolved. Motivated by these experimental developments, we use Monte Carlo simulations of two-dimensional kinetic Ising ferromagnets to study the magnetic relaxation in a negative applied field of a grain with an initial magnetization $m_0 = +1$. The magnetostatic dipole-dipole interactions are treated to lowest order by adding to the Hamiltonian a term proportional to the square of the magnetization. We use droplet theory to predict the functional forms for some quantities observed by MFM, such as the probability that the magnetization is positive. Our simulations are in excellent agreement with droplet-theoretical predictions. The qualitative agreement between experiments and our simulations of switching in individual single-domain ferromagnets indicates that the switching mechanism in such particles may involve local nucleation and subsequent growth of droplets of the stable phase.