Prediction of room-temperature ferromagnetism in a two-dimensional direct band gap semiconductor

Two-dimensional (2D) ferromagnetic (FM) semiconductors with a direct electronic band gap have recently drawn much attention due to their promising potential for spintronic and magneto-optical applications. However, the Curie temperature (T_C) of recently synthesized 2D FM semiconductors is too low (∼45 K) and a room-temperature 2D direct band gap FM semiconductor has never been reported, which hinders the development for practical magneto-optical applications. Here, we show that through isovalent alloying, one can increase the T_C of a 2D FM semiconductor up to room temperature and simultaneously turn it from an indirect to a direct band gap semiconductor. Using the first-principles calculations, we predict that the alloyed CrMoS₂Br₂ monolayer is a direct band gap semiconductor with a T_C of ∼360 K, whereas the pristine CrSBr monolayer is an indirect band gap semiconductor with a T_C of ∼180 K. These findings provide a promising pathway to realize 2D direct band gap FM semiconductors with T_C above room temperature, which will greatly stimulate theoretical and experimental interest in future spintronic and magneto-optical applications.