Skyrmion-Skyrmion Interaction in a Magnetic Film

TL;DR

This study numerically investigates the interactions between skyrmions in a magnetic film, revealing their repulsive behavior, long-range interaction decay, and collapse at close proximity, with implications for magnetic memory design.

Contribution

It provides a detailed numerical analysis of skyrmion-skyrmion interactions, including the effects of DMI and lattice discreteness, and proposes experimental measurement methods.

Findings

Same-chirality skyrmions repel each other.

Interaction decays exponentially with separation, independent of DMI.

Skyrmions collapse into a single one below a critical distance.

Abstract

Interaction of two skyrmions stabilized by the ferromagnetic exchange, Dzyaloshinskii-Moriya interaction (DMI), and external magnetic field has been studied numerically on a 2D lattice of size large compared to the separation, $d$, between the skyrmions. We show that two skyrmions of the same chirality (determined by the symmetry of the crystal) repel. In accordance with earlier analytical results, their long-range pair interaction falls out with the separation as $\exp(-d/\delta_H)$, where $\delta_H$ is the magnetic screening length, independent of the DMI. The prefactor in this expression depends on the DMI that drives the repulsion. The latter results in the spiral motion of the two skyrmions around each other, with the separation between them growing logarithmically with time. When two skyrmions of the total topological charge $Q = 2$ are pushed close to each other, the discreteness of the atomic lattice makes them collapse into one skyrmion of charge $Q = 1$ below a critical separation. Experiment is proposed that would allow one to measure the interaction between two skyrmions by holding them in positions with two magnetic tips. Our findings should be of value for designing topologically protected magnetic memory based upon skyrmions.