Geometrically constrained Skyrmions

TL;DR

This paper demonstrates that thickness modulations in magnetic materials can effectively pin and control the three-dimensional positions of skyrmions, enabling their precise placement for potential device applications.

Contribution

It introduces a method to geometrically constrain skyrmions using thickness variations, supported by micromagnetic simulations and phase diagram analysis.

Findings

Thickness pockets act as skyrmion pinning centers.

Phase diagram maps magnetic states as a function of field and thickness.

Controlled skyrmion positioning is achievable through geometric design.

Abstract

Skyrmions are chiral swirling magnetization structures with nanoscale size. These structures have attracted considerable attention due to their topological stability and promising applicability in nanodevices, since they can be displaced with spin-polarized currents. However, for the comprehensive implementation of skyrmions in devices, it is imperative to also attain control over their geometrical position. Here we show that, through thickness modulations introduced in the host material, it is possible to constrain three-dimensional skyrmions to desired regions. We investigate skyrmion structures in rectangular FeGe platelets with micromagnetic finite element element simulations. First, we establish a phase diagram of the minimum-energy magnetic state as a function of the external magnetic field strength and the film thickness. Using this understanding, we generate preferential sites for skyrmions in the material by introducing dot-like "pockets" of reduced film thickness. We show that these pockets can serve as pinning centers for the skyrmions, thus making it possible to obtain a geometric control of the skyrmion position. This control allows stabilizing skyrmions at positions and in configurations that they would otherwise not attain. Our findings may have implications for technological applications in which skyrmions are used as units of information that are displaced along racetrack-type shift register devices.