  The electronic, magnetic, and topological properties of CoBr2 monolayer are
studied in the frame-work of the density-functional theory (DFT) combined with
tight-binding (TB) modeling in terms of Wannier basis. Our DFT investigation
and Monte Carlo simulation show that there exists intrinsic two-dimensional
ferromagnetism in the CoBr2 monolayer thanks to large out-of-plane
magnetocrystalline anisotropic energy. Our further study shows that the
spin-orbits coupling makes it become a topologically nontrivial insulator with
quantum anomalous Hall effect and topological Chern number 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 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.
