Surface twist instabilities and skyrmion states in chiral ferromagnets

TL;DR

This paper investigates surface twist instabilities in chiral ferromagnets, demonstrating their universal presence and significance in skyrmion formation through experimental and theoretical analysis of MnSi/Si(111) nanolayers.

Contribution

It reveals the universal occurrence of surface chiral twists in non-centrosymmetric magnetic materials and their influence on skyrmion states, supported by experimental data and phenomenological modeling.

Findings

Surface twists are common in chiral magnetic materials.

Surface instabilities influence skyrmion lattice formation.

Experimental evidence in MnSi/Si(111) nanolayers supports theory.

Abstract

In epitaxial MnSi/Si(111) films, the in-plane magnetization saturation is never reached due to the formation of specific surface chiral modulations with the propagation direction perpendicular to the film surfaces [Wilson et al. Phys. Rev. B 88, 214420 (2013)]. In this paper we show that the occurrence of such chiral surface twists is a general effect attributed to all bulk and con- fined magnetic crystals lacking inversion symmetry. We present experimental investigations of this phenomenon in nanolayers of MnSi/Si(111) supported by detailed theoretical analysis within the standard phenomenological model. In magnetic nanolayers with intrinsic or induced chirality, such surface induced instabilities become sizeable effects and play a crucial role in the formation of skyrmion lattices and other nontrivial chiral modulations.