Two-dimensional gallium and indium oxides from global structure searching: Ferromagnetism and half metallicity via hole doping

There has been tremendous research effort in hunting for novel two-dimensional (2D) materials with exotic properties, showing great promise for various potential applications. Here, we report the findings about a new hexagonal phase of 2D Ga₂O₃ and In₂O₃, with high energetic stability, using a global searching method based on an evolutionary algorithm, combined with density functional theory calculations. Their structural and thermal stabilities are investigated by the calculations of their phonon spectra and by ab initio molecular dynamics simulations. They are predicted to be intrinsically non-magnetic stable semiconductors, with a flatband edge around the valence band top, leading to itinerant ferromagnetism and half-metallicity upon hole doping. Bilayer Ga₂O₃ is also studied and found to exhibit ferromagnetism without extra hole doping. The Curie temperature of these materials, estimated using Monte Carlo simulations based on the Heisenberg model, is around 40–60 K upon a moderate hole doping density.