Stable antiferromagnetic property and tunable electronic structure of two-dimensional MnPX3 (X = S and Se) from pristine structure to Janus phase

Abstract 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 MnPX3 (X = S and Se) and Janus Mn2P2S3Se3 monolayers. 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 MnPS3, MnPSe3 and Mn2P2S3Se3 with a valley polarization with consideration of spin–orbital coupling (SOC), respectively. In particular, significant energy-splittings emerge in the SOC-band structures of Janus Mn2P2S3Se3 due 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 of XY model for MnPS3, MnPSe3 and Mn2P2S3Se3, respectively, indicating the XY model 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.