Tunable Magnetism and Half-Metallicity in Hole-Doped Monolayer GaSe

We find, through first-principles calculations, that hole doping induces a ferromagnetic phase transition in monolayer GaSe. Upon increasing hole density, the average spin magnetic moment per carrier increases and reaches a plateau near $1.0text{ }{ensuremath{mu}}_{B}$ per carrier in a range of $3ifmmodetimeselsetexttimesfi{}{10}^{13}/{mathrm{cm}}^{2}ensuremath{-}1ifmmodetimeselsetexttimesfi{}{10}^{14}/{mathrm{cm}}^{2}$, with the system in a half-metal state before the moment starts to descend abruptly. The predicted itinerant magnetism originates from an exchange splitting of electronic states at the top of the valence band, where the density of states exhibits a sharp van Hove singularity in this quasi-two-dimensional system.