Unexpected Asymmetric Mn‐Sb Site Mixing and Reentrant Spin‐Glass State of MnSb 2 Te 4

ABSTRACT Mn‐Sb site mixing directly impacts both the magnetic and topological properties of MnSb 2 Te 4 [MST]. This study reveals that, contrary to previously believed, these anti‐sites can be unevenly distributed within the crystal. The use of High‐Resolution Scanning Transmission Electron Microscopy [STEM] combined with Energy‐Dispersive X‐ray Spectroscopy [EDS] allowed us to identify a local inversion‐breaking asymmetry in the anti‐site distribution within the septuple layers of a polycrystalline sample of MST. This reduced‐symmetry structure warrants further exploration due to its prospect for combining topology and magnetism with other effects, such as the Dzyaloshinskii–Moriya interaction [DMI], non‐linear optics, and piezoelectricity. Direct current [DC] magnetic measurements confirmed the well‐established ferrimagnetic properties of the compound, while alternating current [AC] magnetometry revealed a newly observed reentrant spin‐glass state, representing an important finding for defect‐driven magnetism in topological insulators. A simplified microscopic picture is presented in which antiferromagnetic pockets arise from Mn‐Te‐Mn super‐exchange interactions between Mn defects and Mn planes. The observations are supported by Density Functional Theory [DFT] calculations performed on simplified defect models, which highlight scenarios in which asymmetric site mixing can be energetically favored over symmetric arrangements.