Electrically tunable magnetism and unique intralayer charge transfer in Janus monolayer MnSSe for spintronics applications

Controlling magnetism and electronic properties of two-dimensional (2D) materials by purely electrical means is crucial and highly sought for high-efficiency spintronics devices since electric field can be easily applied locally compared with magnetic field. The recently discovered 2D Janus crystals provide a platform for nanoscale electronics and spintronics due to their broken inversion symmetry. Here, through comprehensive density functional theory calculations and Monte Carlo simulations, we demonstrate that both the electronic and magnetic properties of Janus monolayer MnSSe, a 2D ferromagnetic half-metal with high Curie temperature, are electrically tunable. The exchange coupling can be significantly enhanced or quenched by hole and electron doping, respectively. In particular, with a small amount of hole doping, MnSSe can tune its magnetization easy axis in between out-of-plane and in-plane directions, which is conducive to designing a 2D spin field effect transistor for spin-dependent transport. We also find a reversible longitudinal intralayer charge transfer between S and Se layers that is highly sensitive to the external electric field. Interestingly, the directions of charge flow and the applied field are the same. This behavior originates from the coexistence and/or the competition of external and built-in electric fields. These findings, together with the excellent stability and large in-plane stiffness, can greatly facilitate the development of nanoscale electronics and spintronics devices based on 2D MnSSe crystal.