Intrinsic ferromagnetism and quantum anomalous Hall effect in a CoBr₂ monolayer

The electronic, magnetic, and topological properties of a CoBr₂ monolayer are studied in the framework of density-functional theory (DFT) combined with tight-binding (TB) modeling in terms of the Wannier basis. Our DFT investigation and Monte Carlo simulation show that there exists intrinsic two-dimensional ferromagnetism in the CoBr₂ monolayer, thanks to the large out-of-plane magnetocrystalline anisotropic energy. Our further study indicates that the spin-orbit coupling makes it become a topologically nontrivial insulator with a quantum anomalous Hall effect and topological Chern number [script C] = 4 and its edge states can be manipulated by changing the width of its nanoribbons and applying strains. The CoBr₂ monolayer can be exfoliated from the layered CoBr₂ bulk material because its exfoliation energy is between those of graphene and the MoS₂ monolayer and it is dynamically stable. These results make us believe that the CoBr₂ monolayer can make a promising spintronic material for future high-performance devices.