Thermal Stability of the Magnetization in Perpendicularly Magnetized Thin Film Nanomagnets

TL;DR

This study investigates the thermally induced magnetization reversal in perpendicularly magnetized thin film nanomagnets, revealing that reversal often involves incoherent domain wall motion and that energy barriers depend on element shape and size.

Contribution

The paper introduces a computational approach to analyze reversal dynamics, showing how energy barriers vary with nanomagnet geometry and size, highlighting incoherent reversal mechanisms.

Findings

Reversal often occurs via soliton-like domain walls.

Energy barrier increases with size up to a critical length, then saturates for square elements.

Energy barriers are smaller than those for coherent reversal.

Abstract

Understanding the stability of thin film nanomagnets with perpendicular magnetic anisotropy (PMA) against thermally induced magnetization reversal is important when designing perpendicularly magnetized patterned media and magnetic random access memories. The leading-order dependence of magnetization reversal rates are governed by the energy barrier the system needs to surmount in order for reversal to proceed. In this paper we study the reversal dynamics of these systems and compute the relevant barriers using the string method of E, Vanden-Eijnden, and Ren. We find the reversal to be often spatially incoherent; that is, rather than the magnetization flipping as a rigid unit, reversal proceeds instead through a soliton-like domain wall sweeping through the system. We show that for square nanomagnetic elements the energy barrier increases with element size up to a critical length scale, beyond which the energy barrier is constant. For circular elements the energy barrier continues to increase indefinitely, albeit more slowly beyond a critical size. In both cases the energy barriers are smaller than those expected for coherent magnetization reversal.