Dual Roles of Point Defects in Tuning Ground States and Fermi Level of Magnetic Topological Insulator MnSb₂Te₄

The interplay between intrinsic point defects and the magnetic/topological characteristics of magnetic topological insulators (MTIs) lies at the heart of controlling quantum phenomena. MnSb 2 Te 4 emerges as a promising platform, offering rich defect chemistry and tunable ground states. Here, high‐quality MnSb 2 Te 4 thin films are successfully fabricated using molecular beam epitaxy, where point defects are systematically tuned. Scanning tunneling microscopy revealed Mn Sb and Sb Te antisites as dominant defects exhibiting pronounced clustering behavior, forming Mn Sb ‐rich (7.77–8.47%) and Mn Sb ‐poor (1.84–3.26%) regions with correlated Sb Te defect density. By continuously increasing the Mn flux during growth, the magnetic ground state evolved from antiferromagnetic to ferrimagnetic and finally to a glassy state, driven by the rising Mn Sb concentration and clustering‐induced magnetic frustration. Band structure calculations show that MnSb 2 Te 4 can retain its MTI character under experimentally relevant defect levels, rather than transitioning to a Weyl semimetal phase. Importantly, co‐modulation of Mn Sb and Sb Te defects enable simultaneous optimization of the Fermi level position and ferrimagnetic ordering, overcoming the challenge of strong p ‐type doping. These findings establish a solid foundation for defect‐driven control of magnetism and band topology in MnSb 2 Te 4 , advancing its perspective for hosting the quantum anomalous Hall state.