Oriented Three-Dimensional Magnetic Biskyrmion in MnNiGa Bulk Crystals

TL;DR

This study reveals that biskyrmions in MnNiGa bulk crystals are three-dimensional, disordered structures with in-plane symmetry aligned by magnetocrystalline anisotropy, challenging the view of them as surface-confined objects.

Contribution

It provides the first investigation of the three-dimensional form factor of biskyrmions in bulk crystals using small angle neutron scattering.

Findings

Biskyrmions are disordered in bulk MnNiGa.

Their in-plane symmetry axes align with crystallographic directions.

Magnetocrystalline anisotropy influences biskyrmion orientation.

Abstract

A biskyrmion consists of two bound, topologically stable skyrmion spin textures. These coffee-bean-shaped objects have been observed in real-space in thin plates using Lorentz transmission electron microscopy (LTEM). From LTEM imaging alone, it is not clear whether biskyrmions are surface-confined objects, or, analogously to skyrmions in non-centrosymmetric helimagnets, three-dimensional tube-like structures in bulk sample. Here, we investigate the biskyrmion form factor in single- and polycrystalline MnNiGa samples using small angle neutron scattering (SANS). We find that biskyrmions are not long-range ordered, not even in single-crystals. Surprisingly all of the disordered biskyrmions have their in-plane symmetry axis aligned along certain directions, governed by the magnetocrystalline anisotropy. This anisotropic nature of biskyrmions may be further exploited to encode information.