Title: Two-dimensional chromium bismuthate: A room-temperature Ising ferromagnet with tunable magneto-optical response

Abstract: We present a density functional theory (DFT) based study of a two-dimensional phase of chromium bismuthate (CrBi), previously unknown material with exceptional magnetic and magnetooptical characteristics. Monolayer CrBi is a ferromagnetic metal with strong spin-orbit coupling induced by the heavy bismuth atoms, resulting in a strongly anisotropic Ising-type magnetic ordering with the Curie temperature estimated to be higher than 300 K. The electronic structure of the system is topologically nontrivial, giving rise to a nonzero Berry curvature in the ground magnetic state, leading to the anomalous Hall effect with the conductivity plateau of $\sim$1.5 $e^2/h$ at the Fermi level. Remarkably, the Hall conductivity and the magnetooptical constant are found to be strongly dependent on the direction of magnetization. Besides, monolayer CrBi demonstrates the polar magnetooptical Kerr effect in the visible and near-ultraviolet spectral ranges with the maximum rotation angles of up to 10 mrad. Our findinds suggest that monolayer CrBi is a promising system for practical applications in magnetooptical and spintronic devices.