Topological textures and their bifurcation processes in 2D ferromagnetic thin films

TL;DR

This paper investigates the topological structures and bifurcation processes in 2D ferromagnetic thin films using topological current theory, revealing how vortex-antivortex dynamics influence topological charge and vortex core reversal.

Contribution

It introduces a topological current theory approach to analyze vortex dynamics and topological charge variations in ferromagnetic thin films, highlighting the role of singularities.

Findings

Topological charge changes via vortex-antivortex pair processes.

Vortex merging and splitting affect topological charge and vortex core reversal.

Topological invariants are expressed through Hopf indices and Brouwer degrees.

Abstract

In this paper, by the use of the topological current theory, the topological structures and the dynamic processes in thin-film ferromagnetic systems are investigated directly from viewpoint of topology. It is found that the topological charge of a thin-film ferromagnetic system can be changed by annihilation or creation processes of opposite polarized vortex-antivortex pairs taking place at space-time singularities of the normalized magnetization vector field of the system, the variation of the topological charge is integer and can further be expressed in terms of the Hopf indices and Brouwer degrees of the magnetization vector field around the singularities. Moreover, the change of the topological charge of the system is crucial to vortex core reversal processes in ferromagnetic thin films. With the help of the topological current theory and implicit function theorem, the processes of vortex merging, splitting as well as vortex core