Chiral skyrmions in cubic helimagnet films: The role of uniaxial anisotropy

Abstract

This paper reports on magnetometry and magnetoresistance measurements of MnSi epilayers performed in out-of-plane magnetic fields. We present a theoretical analysis of the chiral modulations that arise in confined cubic helimagnets where the uniaxial anisotropy axis and magnetic field are both out-of-plane. In contrast to in-plane field measurements (Wilson et al., Phys. Rev. B 86, 144420 (2012)), the hard-axis uniaxial anisotropy in MnSi/Si(111) increases the energy of (111)oriented skyrmions and in-plane helicoids relative to the cone phase, and makes the cone phase the only stable magnetic texture below the saturation field. While induced uniaxial anisotropy is important in stabilizing skyrmion lattices and helicoids in other confined cubic helimagnets, the particular anisotropy in MnSi/Si(111) entirely suppresses these states in an out-of-plane magnetic field. However, it is predicted that isolated skyrmions with enlarged sizes exist in MnSi/Si(111) epilayers in a broad range of out-of-plane magnetic fields. These results reveal the importance of the symmetry of the anisotropies in bulk and confined cubic helimagnets in the formation of chiral modulations and they provide additional evidence of the physical nature of the A-phase states in other B20-compounds. 75.70.Ak

New Type of Stable Particlelike States in Chiral Magnets

“…1 are consistent with the continuum theory [18] and experimental data on the direct observation of SkL in thin films of cubic helimagnetic alloys as Fe 1−x Co x Si [11], Mn 1−x Fe x Ge [9], Mn 1−x Fe x Si [19] and pure MnSi [20] and FeGe [21]. The mechanism of SkL stabilization in thin films of cubic helimagnet differs from two-dimensional systems with interface induced DMI [22] and anisotropic bulk helimagnets [23,24]. According to Ref.…”

Neutron study of in-plane skyrmions in MnSi thin films

“…MnSi/Si(111) for film thicknesses greater than 10 nm for out-of-plane fields 37 . A muon-spin rotation study hints at possible additional magnetic phases 38 , and a combined Lorentz microscopy and Hall effect study claims to find evidence for in-plane helicoids and out-of-plane skyrmions 39 .…”

Formation of In-plane Skyrmions in Epitaxial MnSi Thin Films as Revealed by Planar Hall Effect

“…17 Here, to gain insight into this effect, we focus on one other type of skyrmion aggregate, that is, an array of skyrmion rows stretching in the plane of strained MnSi thin films with an in-plane H. 18 Epitaxial MnSi(111) thin films on Si substrates receive a tensile strain due to the lattice mismatch, which increases the hardaxis uniaxial anisotropy along the direction normal to the film plane. 19 Detection of such an in-plane skyrmion formation, however, is challenging experimentally because the established detection methods, such as Lorentz transmission microscopy (TEM) and topological Hall effect, 20,21 are difficult to be applied, in principle, for an in-plane H configuration. Thus far, the formation of the in-plane skyrmion [ Fig.…”