Magnetization Switching in Small Ferromagnetic Particles: Nucleation and Coherent Rotation

TL;DR

This paper investigates thermally activated magnetization switching in small ferromagnetic particles, analyzing the transition from coherent rotation to nucleation as anisotropy varies, using Monte Carlo simulations and theoretical comparisons.

Contribution

It introduces a detailed study of the crossover from coherent rotation to nucleation in magnetization switching, combining simulations with theoretical analysis for different anisotropy regimes.

Findings

Energy barriers from simulations match theoretical predictions.

Switching mechanisms depend on anisotropy strength, transitioning from coherent rotation to nucleation.

Metastable lifetime analysis reveals temperature dependence of switching processes.

Abstract

The mechanisms of thermally activated magnetization switching in small ferromagnetic particles driven by an external magnetic field are investigated. For low uniaxial anisotropy the spins rotate coherently while for sufficiently large uniaxial anisotropy they behave Ising-like, i.e. the switching then is due to nucleation. The crossover from coherent rotation to nucleation is studied for the classical three-dimensional Heisenberg model with uniaxial anisotropy by Monte Carlo simulations. From the temperature dependence of the metastable lifetime the energy barrier of a switching process can be determined. For the case of infinite anisotropy we compare numerical results from simulations of the Ising model with theoretical results for energy barriers for both, single-droplet and multi-droplet nucleation. The simulated barriers are in agreement with the theoretical predictions.