A Micromagnetic Study of Magnetization Reversal in Ferromagnetic Nanorings

TL;DR

This study uses micromagnetic simulations to validate analytical models of magnetization reversal in ferromagnetic nanorings, revealing the conditions under which different transition states occur and identifying new metastable states.

Contribution

It compares micromagnetic simulation results with 1D analytical predictions across various ring geometries, extending understanding of reversal mechanisms and energy landscapes.

Findings

Activation energies closely match analytical predictions.

The 1D approximation holds when ring width is less than radius.

New metastable states are identified in large radius limit.

Abstract

We present results of micromagnetic simulations of thin ferromagnetic rings undergoing magnetization reversal. This geometry is one of few examples in micromagnetics in which the transition states have been found analytically in a 1D model. According to this model, at low fields and large ring sizes, the energetically preferred transition state is a localized magnetization fluctuation (instanton saddle). At high fields and small ring size, the preferred saddle state is a uniformly rotated magnetization (constant saddle). In the first part of this paper, we use numerical micromagnetic simulations to test these predictions of the 1D analytical model for more realistic situations, including a variety of ring radii, annular widths and magnetic fields. The predicted activation energies for magnetization reversal are found to be in close agreement with numerical results, even for rings with a large annular width where the 1D approximation would be expected to break down. We find that this approximation breaks down only when the ring's annular width exceeds its radius. In the second part, we present new metastable states found in the large radius limit and discuss how they provide a more complete understanding of the energy landscape of magnetic nanorings.