Topological defects in flat nanomagnets: the magnetostatic limit

TL;DR

This paper investigates elementary topological defects in thin-film soft magnetic nanoparticles under magnetostatic forces, identifying key defect types and their role in domain wall composition.

Contribution

It characterizes the elementary topological defects in soft magnetic nanoparticles in the magnetostatic limit and explains the composition of domain walls.

Findings

Identifies vortices, cross ties, and edge defects as low-energy topological defects.

Derives topological constraints on domain wall composition.

Confirms the simplest domain wall structure with observations and numerical simulations.

Abstract

We discuss elementary topological defects in soft magnetic nanoparticles in the thin-film geometry. In the limit dominated by magnetostatic forces the low-energy defects are vortices (winding number n = +1), cross ties (n = -1), and edge defects with n = -1/2. We obtain topological constraints on the possible composition of domain walls. The simplest domain wall in this regime is composed of two -1/2 edge defects and a vortex, in accordance with observations and numerics.