Compact Skyrmions, Merons and Bimerons in Thin Chiral Magnetic Films

TL;DR

This paper demonstrates that merons, bimerons, and skyrmions can exist as free, electrically neutral topological excitations in thin chiral magnetic films, supported by an analytic phase diagram aligned with experimental data.

Contribution

It provides a novel analytic approach showing merons as free excitations and constructs a phase diagram for topological phases in chiral magnetic films.

Findings

Merons can exist as free, neutral topological excitations.

The phase diagram includes helix, meron, skyrmion-crystal, skyrmion-gas, and ferromagnet phases.

Experimental data from MnSi and FeCoSi films support the theoretical model.

Abstract

A meron is a controversial topological excitation because it carries just one half of the topological charge unit. It is believed that it is tightly binded to another meron and cannot be observed by isolating it. We present a counter example, investigating the 2-dimensional nonlinear sigma model together with the Dzyaloshinskii-Moriya interaction, where topological excitations are merons, bimerons and skyrmions. They behave as if they were free particles since they are electrically neutral. A prominent feature is that the topological charge density is strictly confined within compact domains. We propose an analytic approach for these compact excitations, and construct a phase diagram. It is comprised of the helix, meron, skyrmion-crystal, skyrmion-gas and ferromagnet phases. It explains quite well the experimental data recently performed in chiral magnets such as MnSi and FeCoSi thin films, as verifies that merons are surely basic topological excitations in the system.