Prediction of manganese trihalides as two-dimensional Dirac half-metals

The recent discovery of intrinsic ferromagnetism in two-dimensional (2D) van der Waals crystals down to the monolayer limit has sparked intense interest due to their potential applications in spintronics. Here, using first-principles calculations we predict that the 2D pristine ${\mathrm{MnX}}_{3}$ (X = F, Cl, Br, I) is a family of intrinsic Dirac half-metals characterized by a band structure with an unusually large gap in one spin channel and a Dirac cone in the other with carrier mobilities comparable to those in graphene. We demonstrate that the ${\mathrm{MnX}}_{3}$ are dynamically and thermodynamically stable up to high temperatures, and exhibit large magnetic moments of about $4\phantom{\rule{4pt}{0ex}}{\ensuremath{\mu}}_{B}$ per ${\mathrm{Mn}}^{3+}$ ion, high Curie temperatures, and large in-plane magnetic anisotropy energy. In addition, the gap opening induced by the spin-orbit coupling drives the lighter systems into the quantum anomalous Hall state. The combination of these unique properties renders this class of 2D ferromagnets a promising platform for high efficiency spintronic applications.