Novel two-dimensional ferromagnetic semiconductors: Ga-based transition-metal trichalcogenide monolayers

Ga-based two-dimensional transition-metal trichalcogenides with tunable ferromagnetic semiconducting properties are explored by first-principles calculations. It is found that the CrGaTe₃ monolayer is an intrinsic ferromagnetic semiconductor with an indirect bandgap of 0.3 eV and exhibits strong dynamical, thermal and mechanical stabilities in the free-standing form. Its Curie temperature of 71 K estimated by Monte Carlo simulations can be significantly enhanced up to near room-temperature (263 K) by 5% biaxial tensile strain at which its structure still remains dynamically stable, while compressive strain can turn the monolayer from a ferromagnetic semiconductor to an antiferromagnetic semiconductor and finally to a ferromagnetic metal with a Curie temperature of 473 K at -5% strain. It is revealed that the pronounced strain tunability originates from the competition between a variety of magnetic exchange interactions. The CrGaSe₃ monolayer is found to exhibit similar intrinsic ferromagnetic semiconducting properties and strain tunability. The exceptional properties render Ga-based transition-metal trichalcogenides promising candidates for spintronic applications.