Antiskyrmions and anisotropic magnetic domain structures in S₄ symmetry magnets

Antiskyrmions, new topological spin textures with topological numbers of opposite sign to those of skyrmions, have attracted much attention in the research field of topological magnetism. Antiskyrmions are stabilized by anisotropic Dzyaloshinskii–Moriya interaction and magnetic dipolar interaction in non-centrosymmetric magnets with D_2d and S₄ symmetry. Thus far, however, antiskyrmion studies have been restricted to Heusler alloys with D_2d symmetry. Recently, we have discovered a new antiskyrmion-host material with S₄ symmetry, Pd-doped schreibersite (Fe,Ni,Pd)₃P. Antiskyrmions were observed in thin plates over a wide temperature region, including room temperature, using Lorentz transmission electron microscopy [1]. Furthermore, antiskyrmions and elliptic skyrmions were found to be interconverted by varying magnetic field and lamella thickness. Systematic compositional tuning studies have revealed that the stability of antiskyrmions is governed by uniaxial magnetic anisotropy and demagnetization energy, as well as anisotropic Dzyaloshinskii–Moriya interaction [2]. Because of the important role of magnetic dipolar interaction, the magnetic texture size increases and the magnetic domain pattern becomes more complex with increasing crystal thickness. Magnetic force microscopy has shown that sawtooth-shaped anisotropic fractal magnetic domain patterns appear near the surface of thick crystals. In addition, small-angle neutron scattering measurements have revealed a three-dimensional fractal structure of the magnetic domain walls in bulk single crystals [3].