Conversation from antiferromagnetic MnBr₂ to ferromagnetic Mn₃Br₈ monolayer with large MAE

A pressing need in low energy spintronics is two-dimensional (2D) ferromagnets with Curie temperature above the liquid-nitrogen temperature (77 K), and sizeable magnetic anisotropy. We studied Mn₃Br₈ monolayer which is obtained via inducing Mn vacancy at 1/4 population in MnBr₂ monolayer. Such defective configuration is designed to change the coordination structure of the Mn-d⁵ and achieve ferromagnetism with sizeable magnetic anisotropy energy (MAE). Our calculations show that Mn₃Br₈ monolayer is a ferromagnetic (FM) half-metal with Curie temperature of 130 K, large MAE of - 2.33 meV per formula unit, and atomic magnetic moment of 13/3μ_B for the Mn atom_. Additionally, Mn₃Br₈ monolayer maintains to be FM under small biaxial strain, whose Curie temperature under 5% compressive strain is 160 K. Additionally, both biaxial strain and carrier doping make the MAE increases, which mainly contributed by the magneto-crystalline anisotropy energy (MCE). Our designed defective structure of MnBr₂ monolayer provides a simple but effective way to achieve ferromagnetism with large MAE in 2D materials.