Surface Roughness Dominated Pinning Mechanism of Magnetic Vortices in Soft Ferromagnetic Films

TL;DR

This study reveals that surface roughness at a specific length scale is the primary factor pinning magnetic vortices in soft ferromagnetic films, providing a new characterization approach for understanding domain wall behavior.

Contribution

The paper introduces a quantitative method to link surface roughness with vortex pinning mechanisms in soft ferromagnetic films, highlighting the importance of thickness fluctuations.

Findings

Pinning of magnetic vortices correlates strongly with surface roughness.

Thickness fluctuations at the vortex core scale dominate pinning.

The mechanism is likely universal in soft ferromagnetic films.

Abstract

Although pinning of domain walls in ferromagnets is ubiquitous, the absence of an appropriate characterization tool has limited the ability to correlate the physical and magnetic microstructures of ferromagnetic films with specific pinning mechanisms. Here, we show that the pinning of a magnetic vortex, the simplest possible domain structure in soft ferromagnets, is strongly correlated with surface roughness, and we make a quantitative comparison of the pinning energy and spatial range in films of various thickness. The results demonstrate that thickness fluctuations on the lateral length scale of the vortex core diameter, i.e. an effective roughness at a specific length scale, provides the dominant pinning mechanism. We argue that this mechanism will be important in virtually any soft ferromagnetic film.