Magnetic anisotropy of two-dimensional ferromagnetic insulator MnBi₂Te₄

MnBi₂Te₄ has attracted great interest recently due to its magnetic and topological properties. Based on the density functional theory calculation, we systematically study the magnetic anisotropy of the monolayer MnBi₂Te₄, which is vital for establishing the long-range magnetic order in two-dimensional system. We find the exchange interaction in monolayer MnBi₂Te₄ almost has no contribution to the magnetic anisotropy, as a result of the weak p-d hybridization between Mn and Te. The magnetic anisotropy originates from the single-ion anisotropy, leading to a ferromagnetic Curie temperature of about 20 K. Interestingly, the emergence of the single-ion anisotropy cannot be induced solely by the spin-orbit coupling of Mn atoms, but also involves the spin-orbit coupling of ligand Te. This behavior is very different from that in monolayer CrI₃ and CrGeTe₃. Our findings may provide a comprehensive understanding of the magnetic behavior in monolayer MnBi₂Te₄ and motivate further research on its potential applications.