Ultra-thin Heusler films and lamellae that host non-collinear spin textures

Abstract

The recent discovery of anti-skyrmions[1] and elliptical block skyrmions[2] in lamellae formed from single crystals of inverse tetragonal ternary Heusler compounds makes these compounds extremely interesting. Related binary compounds host chiral domain walls whose current induced motion in films that are only 1 unit cell thick has recently been observed. These films were prepared using a novel method of chemical templating[3]. We show that strain can dramatically affect the current induced domain wall motion in such films, changing both its magnitude and, remarkably, even its direction. Anti-skyrmions are extremely interesting objects that have high stability[4] and whose size can be tuned by more than an order of magnitude [5] by varying the thickness of the host lamella. These properties derive from the symmetry of the bulk Dzyaloshinskii-Moriya vector exchange interaction that stabilizes them that itself is derived from their underlying crystal structure. We have found similar properties in other materials with related symmetries[6]. The current induced motion of anti-skyrmions has not yet been realized but theoretical models suggest that the skyrmion Hall angle will vary strongly with current direction and, for certain crystal directions, will be zero. Whilst we have found no evidence, to date, for current induced motion of such objects from volume spin-transfer torques, models show that spin-orbit torques should give rise to their motion. For this purpose, ultra-thin 2D layers are needed that can be coupled to heavy metal layers in which spin currents can be generated. In this talk we discuss progress in preparing high quality, epitaxial, ultra-thin films of ternary inverse tetragonal Heusler compounds that are only 1 to 2 unit cells thick and the exploration of non collinear spin textures in these films as well as their current induced motion. Finally, we discuss the first observation of fractional anti-skyrmions and Block skyrmions in nano-stripes formed from inverse tetragonal ternary Heusler compounds. **