Enhanced Magnetic Anisotropy and Curie Temperature by the Absence of Se Atoms at the Interface of EuS/Bi2Se3

The heterojunction composed of ferromagnetic insulator (EuS) and topological insulator (Bi2Se3) is interesting due to several unusual behaviors produced by the interfacial effects. Previous experiments suggest a largely enhanced Curie temperature up to room temperature and perpendicular magnetic anisotropy at the interface [F. Katmis et al., Nature 533, 513 (2016).]. However, a recent experiment indicates that room-temperature ferromagnetic behavior is absent, and only in-plane anisotropy is observed [A.I. Figueroa et al., PRL 125, 226 801 (2020).]. To understand the puzzling observations in EuS/Bi2Se3, Se-missing interfacial system is constructed and the magnetic anisotropy energy and the Curie temperature based on density functional calculations are studied. The results suggest that the absence of Se atoms greatly enhance the perpendicular magnetic anisotropy and the estimated Curie temperature based on Ising model can be up to room temperature. Therefore, the puzzling observations may be concerned with the details of the interfacial system.