Homogeneous and heterogeneous nucleation of skyrmions in thin layers of cubic helimagnets

TL;DR

This paper investigates the formation and stability of isolated skyrmions in thin cubic helimagnet layers, analyzing homogeneous and heterogeneous nucleation via torons and bobbers, and compares magnetic torons with liquid crystal torons.

Contribution

It provides a theoretical analysis of skyrmion nucleation mechanisms, stability conditions, and the role of anisotropic contributions in cubic helimagnets, highlighting differences from liquid crystal torons.

Findings

Skyrmions can form via elongation of torons and bobbers.

Small anisotropic effects facilitate skyrmion core formation.

Magnetic torons have compatibility issues with surrounding phases.

Abstract

Formation of isolated chiral skyrmions by homogeneous and heterogeneous nucleation has been studied in thin layers of cubic helimagnets via elongation of torons and chiral bobbers, correspondingly. Both torons and bobbers are localized in three dimensions, contain singularities, and according to the theoretical analysis within the standard phenomenological models can exist as metastable states in saturated and modulated phases of noncentrosymmetric ferromagnets. Their elongation into the defect-free skyrmion filament is facilitated by small anisotropic contributions making skyrmion cores negative with respect to the surrounding parental state. We show that isolated magnetic torons pose the same problem of compatibility with a surrounding phase as the torons in confinement-frustrated chiral nematics [I. Smalyukh et al., Nature Mater 9, 139-145 (2010)]. We underline the distinct features of magnetic and liquid-crystals torons and calculate phase diagrams indicating their stability regions.