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

TL;DR

This study visualizes the magnetic domain structure of MnSb$_2$Te$_4$, a magnetic topological insulator with a Curie temperature around $T_C \approx 45\,\mathrm{K}$, using high-resolution Bitter decoration. Magnetotransport confirms soft ferromagnetism with a coercive field $H_c \sim 100\,\mathrm{Oe}$, and the decoration reveals a hierarchical two-scale domain texture localized to portions of the surface. The authors interpret this as evidence for two magnetically weakly coupled subsystems—surface and bulk—driven by an inhomogeneous distribution of Mn$_{Sb}$ antisite defects and possible near-surface symmetry breaking. This work advances understanding of surface-bulk magnetic stratification in van der Waals magnetic topological materials and informs strategies to engineer domain structures for spintronic and QAHE-related applications; it also calls for further micromagnetic modeling and systematic cross-sample studies across different $T_C$ values.

Abstract

The domain structure of a MnSb$_2$Te$_4$ single crystal with a Curie temperature $T_C \approx 45~K$ 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 $\mathrm{Mn_{Sb}}$ antisite defects, with an additional contribution from symmetry breaking in the near-surface layer.

Figures (3)

• Figure 1: (Color Online) Magnetotransport properties of a $\mathrm{MnSb_2Te_4}$ single crystal. (a) Temperature dependence of the resistivity $\rho(T)$ measured in zero magnetic field. (b) Transverse (Hall) resistivity $\rho_{xy}$ as a function of the perpendicular magnetic field $B$, measured at different temperatures.
• Figure 2: (Color Online) Micrographs of the surface and decoration patterns of a $\mathrm{MnSb_2Te_4}$ single crystal. (a) Overview of the crystal surface obtained by optical microscopy. (b)--(f) Images of the magnetic flux structure in different regions of the sample obtained by decoration with magnetic nanoparticles and visualized by scanning electron microscopy: (b) region 1; (c) region 2; (d,e) region 3; (f) region 4.
• Figure 3: (Color Online) Comparative analysis of the domain structure in $\mathrm{MnSb_2Te_4}$. (a,b) Domain morphology obtained after decoration with magnetic nanoparticles, visualized by optical microscopy (a) and scanning electron microscopy (b). (c,d) Spatial frequency analysis highlighting the large-scale (c) and small-scale (d) components of the domain structure. (e,f) Binarized images corresponding to the large-scale (e) and small-scale (f) domain textures.