Ferromagnetic MnSb₂Te₄: A p-type topological insulator with magnetic gap closing at high Curie temperatures of 45-50 K

Mn enables the formation of intrinsic magnetic topological insulators for the quantum anomalous Hall effect with A₁B₂C₄ stoichiometry, e. g., antiferromagnetic MnBi₂Te₄ with 25 K Néel temperature. Here, we show that p-type MnSb₂Te₄, previously considered topologically trivial, is a ferromagnetic topological insulator with high Curie temperature of 45 to 50 K. It displays out-of-plane magnetic anisotropy, the nontrivial topology is robust in band structure calculations towards magnetic disorder, provides a Dirac point of the topological surface state close to the Fermi level with out-of-plane spin polarization in spin-ARPES, and exhibits a magnetically induced band gap of 17 meV that closes at the Curie temperature as demonstrated by scanning tunneling spectroscopy. Moreover, it displays a critical exponent of magnetization β≈1, indicating the vicinity of a quantum critical point. We identify the influences of structural and magnetic disorder that render MnSb₂Te₄ the ideal system for tuning electric and magnetic properties of quantum anomalous Hall systems.