Janus MoCrSSe monolayer: A strong two dimensional polar antiferromagnet

Y The introduction of Janus structure into a two-dimensional (2D) monolayer offers a new degree of freedom for controlling their electronic, optical and spin properties. Also, intrinsic magnetism in 2D monolayers is highly expected for low dimensional spintronic and quantum-information devices. In this work, we have combined them, demonstrating an outstanding new 2D Janus MoCrSSe monolayer with an internal anti-ferromagnetic ground state. The Janus monolayer can be synthesized by deposing Cr atoms on the MoSSe monolayer. The magnetic moments originate in Cr atoms, and the anti-ferromagnetic coupling between them is very strong. The energy difference between anti-ferromagnetic and ferromagnetic orders exceeds 230 meV per magnetic atom. The magnetic moment of Cr are robust against external strains, and the magnetic coupling between them can be further increased by tensile strains. The ground anti-ferromagnetic state of MoCrSSe is electronically insulating with a band gap of approximately 0.4 eV, which indicates its use for infrared photodetection. Interestingly, MoCrSSe becomes electrically conductive in the ferromagnetic state. This phase transition demonstrates its ability as magnetic switch. Our results provide crucial guidelines for implementing MoCrSSe monolayer as a component for spintronic and optoelectronic devices.