Microscopic mechanisms of magnetization reversal

TL;DR

This paper explores two distinct microscopic mechanisms of magnetization reversal in ferromagnetic films, deriving dynamic equations for each scenario and analyzing their conditions and characteristics.

Contribution

It introduces a comprehensive micromagnetic approach for describing magnetization reversal, including a novel tensor damping term and nonlinear spin-wave resonance effects.

Findings

Derived a general dynamic equation with tensor damping for coherent reversal.

Developed an analytic micromagnetic model for nonlinear spin-wave induced reversal.

Identified conditions favoring each reversal scenario.

Abstract

Two principal scenarios of magnetization reversal are considered. In the first scenario all spins perform coherent motion and an excess of magnetic energy directly goes to a nonmagnetic thermal bath. A general dynamic equation is derived which includes a tensor damping term similar to the Bloch-Bloembergen form but the magnetization magnitude remains constant for any deviation from equilibrium. In the second reversal scenario, the absolute value of the averaged sample magnetization is decreased by a rapid excitation of nonlinear spin-wave resonances by uniform magnetization precession. We have developed an analytic k-space micromagnetic approach that describes this entire reversal process in an ultra-thin soft ferromagnetic film for up to 90^{o} deviation from equilibrium. Conditions for the occurrence of the two scenarios are discussed.