Abstract

Magnetic skyrmions are nowadays found in a variety of different material classes, ranging from single crystals to sputtered films. They often emerge on length scales much larger than the atomic lattice where they appear as vortex-like, rotationally symmetric whirls. Their anti-vortex-like partners, consequently dubbed anti-skyrmions, naturally break this rotational symmetry which leads to a plethora of new effects. However, only a limited number of antiskyrmion-hosting materials are known and, previously, they all belonged to the D2d symmetry class, even though crystals with S4 symmetry were predicted to also host antiskyrmions.[1]

I will present our recent works on antiskyrmions in crystals with S4 symmetry. Combining experiments and theory, we studied antiskyrmions, skyrmions, and other textures in the S4-symmetric family of schreibersites (Fe,Ni)3P with heavy element doping.[2,3,4,5] The competition between the dominant demagnetization energy and small Dzyaloshinskii-Moriya interaction stabilizes both antiskyrmions and skyrmions in the transition region from the stripe phase to the field-aligned ferromagnet and, moreover, renders antiskyrmions square-shaped and skyrmions elliptical.[2] In general, antiskyrmions form in thicker samples and samples with larger uniaxial anisotropy where the bulk DMI can compete with dipolar interactions. Vice versa, skyrmions form in thinner samples where they profit from the strong dipolar interaction.[3] Moreover, I will show how the ellipticity of skyrmions in these systems can be used to estimate the magnitude of the DMI[4] and that, for a broad range of material parameters, antiskyrmions are actually composite mixed-topology skyrmions, i.e., a new type of magnetic texture which is both skyrmion and antiskyrmion.[5]

[1] A. N. Bogdanov and D. A. Yablonskii, Sov. Phys. JETP 68, 101-103 (1989).
[2] K. Karube, L. C. Peng, J. Masell, et al., Nat. Mater. 20, 335-340 (2021).
[3] K. Karube, L. C. Peng, J. Masell, et al., Adv. Mater. 202108770 (2022).
[4] S. Schneider, J. Masell, F. S. Yasin, et al. (in preparation).
[5] F. S. Yasin, J. Masell, et al. (in preparation).