Stable antiferromagnetic property and tunable electronic structure of two-dimensional MnPX(X = S and Se) from pristine structure to Janus phase.

Transition-metal phosphorus trichalcogenides have been considered as very promising two-dimensional (2D) magnetic candidates up-to-date. We performed a systematical first-principles study on the electronic structures and magnetic properties of pristine MnPX(X = S and Se) and Janus MnPSSemonolayers. All monolayers behave as a direct-band-gap semiconductor in antiferromagnetic ground state which is caused by strong direct and indirect exchange interactions. It is found that the electronic structures and magnetic properties can be manipulated by Janus phase. The calculated band gap is 2.44 eV, 1.80 eV and 1.86 eV for MnPS, MnPSeand MnPSSewith a valley polarization with consideration of spin-orbital coupling (SOC), respectively. In particular, significant energy-splittings emerge in the SOC-band structures of Janus MnPSSedue to its broken-inversion-symmetry. Estimated by Monte Carlo simulations, the Néel temperature is 96 K, 71 K and 79 K based on Ising model while halved down to 41 K, 33 K and 36 K on the basis ofmodel for MnPS, MnPSeand MnPSSe, respectively, indicating themodel should be more reliable to describe the spin dynamics. Our research offers an insight into the magnetic mechanism and paves a feasible path to modulate the magnetism for 2D magnets in realistic applications on spintronics.