Effect of Misfit Strains on the Skyrmion Crystal Phase in Epitaxial Thin Films of Helimagnets

Abstract

A novel form of thermodynamic potential is derived for an eptaxial helimagnetic thin film suffering a general form of mechanical loads. The three effects misfit strains can have on the skyrmion crystal (SkX) phase of the thin film have been elucidated: they change the Curie temperature, modify the stability of the phase, and distort the field configuration of SkX by inducing an anisotropy to the Dzyaloshinskii–Moriya (DM) interaction. Using the theory, the misfit strain–magnetic field phase diagram for MnSi thin film, which explains the enhanced stability of SkX phase in the MnSi/Si thin film previously not understood has been plotted. It has also been shown that moderate misfit strains may lead to anisotropic DM interaction whose anisotropy depends on the magnetoelastic coefficients of the material. As the anisotropy of DM interaction increases, the SkX is gradually distorted, which eventually becomes unstable and transforms to an elongated “double‐Q” structure.