Visualizing Temperature Driven Ferromagnetic to Antiferromagnetic Transition in MnSb₂Te₄

The intrinsic magnetic topological insulator MnBi₂Te₄ exhibits rich exotic quantum phenomena^1,2. However, the theoretically predicted Dirac mass gap is susceptible to the native magnetic defects, which often leads to conducting bulk state³. Therefore, understanding the role of magnetic defect essential in engineering topological materials. The same type of magnetic defects in the isostructural compound MnSb₂Te₄ shows higher concentration and tunability, making MnSb₂Te₄ an ideal platform to investigate the interplay among magnetic defect, topological band structure and magnetism. It has been reported that by tuning the Mn/Sb site mixing, ferromagnetic (FM) order can be introduced into MnSb₂Te₄ and compete with the antiferromagnetic order⁴. Magnetic imaging of ferromagnetic domains in some site mixing engineered MnSb₂Te₄ systems has been reported in our previous work⁵. In this work, we directly visualize the temperature driven FM-AFM phase transition with T_C = 24 K and T_N = 15 K in single crystals of MnSb₂Te₄ using cryogenic Magnetic Force Microscopy. Our work reveals the complex magnetic competition in MnSb2Te4 and paves the way for understanding the role of magnetic defect in the magnetism of MnSb2Te4.