Unpinning the skyrmion lattice in MnSi:Effect of substitutional disorder

TL;DR

This study investigates how substitutional disorder in MnSi, caused by Ga and Ir doping, affects the skyrmion lattice and helical order, revealing reduced pinning and increased energy barriers for reorientation.

Contribution

It provides new insights into how substitutional disorder influences skyrmion lattice pinning and domain reorientation in MnSi-based materials.

Findings

Substitutional disorder reduces SKL pinning to the crystal lattice.

Heavier element doping increases energy barriers for domain reorientation.

Disorder affects SKL alignment depending on magnetic field orientation.

Abstract

By employing magnetization and small angle neutron scattering (SANS) measurements, we have investigated the behavior of the skyrmion lattice (SKL) and the helical order in MnSi0.992Ga0.008. Our results indicate that the order of the SKL is sensitive to the orientation of an applied magnetic field with respect to the crystal lattice and small variations in the sequence of temperature and applied magnetic field changes. The disorder caused by the substitution of the heavier element Ga for Si is sufficient to reduce the pinning of the SKL to the underlying crystalline lattice. This reduces the propensity for the SKL to be aligned with the crystal lattice. This tendency is most evident when the applied field is not well oriented with respect to the high symmetry axes of the crystal resulting in disorder in the long range SKL while maintaining sharp radial order. We have also investigated the effect of substituting heavier elements into MnSi on the reorientation process of the helical domains with field cycling in MnSi0.992Ga0.008 and Mn0.985Ir0.015Si. A comparison of the reorientation process in these materials with field reduction indicates that the substitution of heavier elements on either Mn or Si sites creates a higher energy barrier for the reorientation of the helical order and for the formation of domains.