Effects of boundary conditions on magnetization switching in kinetic Ising models of nanoscale ferromagnets

TL;DR

This paper investigates how different boundary conditions affect magnetization switching in nanoscale ferromagnets modeled by kinetic Ising systems, revealing boundary-dependent behaviors and a size-dependent switching field peak.

Contribution

It extends droplet theory to analyze boundary effects on magnetization switching, supported by Monte Carlo simulations with various boundary conditions and system shapes.

Findings

Boundary conditions significantly influence switching behavior.

A peak in switching field depends on system size and boundary type.

Open boundaries can diminish or eliminate the switching field peak.

Abstract

Magnetization switching in highly anisotropic single-domain ferromagnets has been previously shown to be qualitatively described by the droplet theory of metastable decay and simulations of two-dimensional kinetic Ising systems with periodic boundary conditions. In this article we consider the effects of boundary conditions on the switching phenomena. A rich range of behaviors is predicted by droplet theory: the specific mechanism by which switching occurs depends on the structure of the boundary, the particle size, the temperature, and the strength of the applied field. The theory predicts the existence of a peak in the switching field as a function of system size in both systems with periodic boundary conditions and in systems with boundaries. The size of the peak is strongly dependent on the boundary effects. It is generally reduced by open boundary conditions, and in some cases it disappears if the boundaries are too favorable towards nucleation. However, we also demonstrate conditions under which the peak remains discernible. This peak arises as a purely dynamic effect and is not related to the possible existence of multiple domains. We illustrate the predictions of droplet theory by Monte Carlo simulations of two-dimensional Ising systems with various system shapes and boundary conditions.