  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 discover 2D Janus crystals
has provide a new platform for nanoscale electronics and spintronics due to
their broken inversion symmetry nature. The intrinsic ferromagnetic Jauns
monolayer, and hence the tunable physical properties, is therefore of great
interest. Here, through comprehensive density functional theory calculations
and Monte Carlo simulations, we unveil that single-layer MnSSe is an intrinsic
ferromagnetic half-metal with a direct band gap of 1.14 eV in spin-down channel
and a Curie temperature of about 72 K. The exchange coupling can be
significantly enhanced or quenched by hole and electron doping, respectively.
In particular, 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 2D spin field-effect transistor for spin-dependent transport. We
also find a reversible longitudinal interlayer charge transfer between S and Se
layers for the first time that is highly sensitive to the applied external
electric field. Interestingly, the directions of charge flow and the applied
field are the same. The behavior originates from the coexistence and/or the
competition of external and built-in 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.
