Two-Dimensional Chromium Bismuthate: A Room-Temperature Ising Ferromagnet with Tunable Magneto-Optical Response

We present a density-functional-theory-based study of a two-dimensional phase of chromium bismuthate (CrBi), a previously unknown material with exceptional magnetic and magneto-optical 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 a conductivity plateau of about 1.5 e2/h at the Fermi level. Remarkably, the Hall conductivity and the magneto-optical constant are found to be strongly dependent on the direction of magnetization. Besides, monolayer CrBi demonstrates the polar magneto-optical Kerr effect in the visible and near-ultraviolet spectral ranges with the maximum rotation angles of up to 10 mrad. Our findings suggest that monolayer CrBi is a promising system for practical applications in magneto-optical and spintronic devices.