Sub-domain structure in a single crystal of the magnetic topological insulator MnSb2Te4

The domain structure of a MnSb${}_2$Te${}_4$ single crystal with a Curie temperature $T_C\approx 45K$ was studied using the high-resolution Bitter decoration technique. Magnetotransport measurements confirm a soft ferromagnetic ordering with a coercive field of $\sim 100$ Oe. We revealed the formation of a hierarchical domain structure characterized by two distinct spatial scales. These results indicate the existence of two magnetically weakly coupled subsystems – surface and bulk. The observed sub-domain structure can be attributed to the formation of a ferromagnetic well due to an inhomogeneous distribution of $\mathrm{M}{\mathrm{n}}_{\mathrm{S}\mathrm{b}}$ antisite defects, with an additional contribution from symmetry breaking in the near-surface layer.