Viscous dynamics of vortices in a ferromagnetic film

TL;DR

This paper derives the viscous forces acting on vortices in a thin ferromagnetic film, revealing long-range interactions and mutual drag effects that influence vortex dynamics.

Contribution

It introduces a comprehensive model for viscous forces on vortices, accounting for long-range interactions and mutual drag tensors in ferromagnetic thin films.

Findings

Mutual drag tensor is comparable to self-drag coefficient.

Viscous forces are a linear superposition of vortex velocities.

Long-range vortex interactions significantly affect vortex dynamics.

Abstract

We derive viscous forces for vortices in a thin-film ferromagnet. The viscous force acting on vortex $i$ is a linear superposition $\mathbf F_i = - \sum_{j} \hat{D}_{ij} \mathbf V_j$, where $\mathbf V_j$ is the velocity of vortex $j$. Thanks to the long-range nature of vortices, the mutual drag tensor $\hat{D}_{ij}$ is comparable in magnitude to the coefficient of self-drag $D_{ii}$.