Rotating vortex dipoles in ferromagnets

TL;DR

This paper investigates the properties and dynamics of rotating vortex dipoles in ferromagnets, analyzing their energy, rotation frequencies, and topological charge changes, with implications for magnetic topological defects like Bloch Points.

Contribution

It provides a theoretical and numerical analysis of vortex-antivortex pairs as rotating dipoles, revealing their energy dependence, annihilation process, and impact on topological charge dynamics in ferromagnets.

Findings

Energy as a function of angular momentum characterized

Confirmed rotation frequencies through numerical simulations

Described annihilation process affecting topological charge

Abstract

Vortex-antivortex pairs are localized excitations and have been found to be spontaneously created in magnetic elements. In the case that the vortex and the antivortex have opposite polarities the pair has a nonzero topological charge, and it behaves as a rotating vortex dipole. We find theoretically, and confirm numerically, the form of the energy as a function of the angular momentum of the system and the associated rotation frequencies. We discuss the process of annihilation of the pair which changes the topological charge of the system by unity while its energy is monotonically decreasing. Such a change in the topological charge affects profoundly the dynamics in the magnetic system. We finally discuss the connection of our results with Bloch Points (BP) and the implications for BP dynamics.