Observation of Néel-type skyrmions in acentric self-intercalated Cr1+ ?Te2
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Here, Saha et al. show that self-intercalation of e(2)Cr atoms in CrTe2 create an asymmetry in the number of atoms intercalated in the van der Waals gaps between the layers of CrTe2. This inversion symmetry breaking leads to non-collinear spin-textures and Neel-type magnetic skyrmions over a wide temperature range.
Transition-metal dichalcogenides intercalated with 3d-transition metals within the van der Waals (vdW) gaps have been the focus of intense investigations owing to their fascinating structural and magnetic properties. At certain concentrations the intercalated atoms form ordered superstructures that exhibit ferromagnetic or anti-ferromagnetic ordering. Here we show that the self-intercalated compound Cr1+delta Te2 with delta approximate to 0.3 exhibits a new, so far unseen, three-dimensionally ordered (2x2x2) superstructure. Furthermore, high resolution X-ray diffraction reveals that there is an asymmetric occupation of the two inequivalent vdW gaps in the unit cell. The structure thus lacks inversion symmetry, which, thereby, allows for chiral non-collinear magnetic nanostructures. Indeed, Neel-type skyrmions are directly observed using Lorentz transmission electron microscopy. The skyrmions are stable within the accessible temperature range (100-200 K) as well as in zero magnetic field. The diameter of the Neel skyrmions increases with lamella thickness and varies with applied magnetic field, indicating the role of long-range dipole fields. Our studies show that self-intercalation in vdW materials is a novel route to the formation of synthetic non-collinear spin textures.