Skyrmions with varying size and helicity in composition-spread helimagnetic alloys

TL;DR

This study explores how skyrmion size and helicity vary in helimagnetic alloys with composition, revealing a correlation with crystal chirality and SOC strength, and demonstrating tunability of skyrmion properties.

Contribution

It demonstrates the relationship between skyrmion helicity and crystal chirality in composition-spread alloys and shows how SOC variation influences skyrmion size and helicity.

Findings

Skyrmion size varies non-monotonously with composition.

Reversal of helicity-chirality correlation at x=0.8.

SOC strength sign reversal affects skyrmion properties.

Abstract

The chirality, i.e. left or right handedness, is an important notion in a broad range of science. In condensed matter, this occurs not only in molecular or crystal forms but also in magnetic structures. A magnetic skyrmion, a topologically-stable spin vortex structure, as observed in chiral-lattice helimagnets is one such example; the spin swirling direction (skyrmion helicity) should be closely related to the underlying lattice chirality via the relativistic spin-orbit coupling (SOC). Here, we report on the correlation between skyrmion helicity and crystal chirality as observed by Lorentz transmission electron microscopy (TEM) and convergent-beam electron diffraction (CBED) on the composition-spread alloys of helimagnets Mn1-xFexGe over a broad range (x = 0.3 - 1.0) of the composition. The skyrmion lattice constant or the skyrmion size shows non-monotonous variation with the composition x, accompanying a divergent behavior around x = 0.8, where the correlation between magnetic helicity and crystal chirality is reversed. The underlying mechanism is a continuous x-variation of the SOC strength accompanying sign reversal in the metallic alloys. This may offer a promising way to tune the skyrmion size and helicity.