Electronic phase transition, perpendicular magnetic anisotropy and high Curie temperature in Janus FeClF

Abstract How to enhance the spin polarization, the Curie temperature and the perpendicular magnetic anisotropy (PMA) is crucial for the applications of 2D magnets in spintronic devices. In this work, based on the experimental FeCl 2 flakes and the predicted in-plane magnetic anisotropy (IMA) and lower Curie temperature of FeCl 2 monolayer, we use first-principles and Monte Carlo simulation to explore the strain and carrier-doping effects on the electronic and magnetic properties of Janus FeClF monolayer. The structure is stable within −10% to 2% biaxial strain. Janus FeClF monolayer can experience transitions from a half-semiconductor to a spin gapless semiconductor (SGS) around the −6% compressive strain, and from the IMA to the PMA at the −7% compressive strain. The super-exchange Fe–F/Cl–Fe interaction induces the ferromagnetic coupling, and the Curie temperature can be considerably enhanced from 56 K to 281 K at the −10% compressive strain. The half-metallicity can be achieved whether under electron doping or hole doping. The Fe- d orbitals and the spin–orbit coupling interaction between occupied and unoccupied intraorbital states are responsible for the electronic phase transition and the magnetic anisotropy, respectively. Remarkably, the compressive −10% strain and the 0.02 e doping collectively increase the Curie temperature to near room temperature (286 K). The high spin polarization (exhibiting SGS and half-metal), the PMA and the near-room-temperature ferromagnetism induced by strain and doping make Janus FeClF a promising candidate for 2D spintronic applications, which will stimulate experimental and theoretical broad studies on this class of Janus monolayers FeXY (X,Y = F, Cl, Br, and X ≠ Y).