Unusual Dirac half-metallicity with intrinsic ferromagnetism in vanadium trihalide monolayers

摘要

The Dirac half-metallicity (H. Ishizuka et al., Phys. Rev. Lett. 2012, 109, 237207, Li et al. Phys. Rev. B: Condens. Matter Mater. Phys., 2015, 92, 201403(R)) with a gap in one spin channel but a Dirac cone in the other has been proposed and attracted considerable attention. We report these exciting properties for VCl3 and VI3 layered materials based on density functional theory combined with the self-consistently determined Hubbard U approach (DFT+U-scf). Using DFT+U-scf, the stability and electronic and magnetic structures of VCl3 and VI3 monolayers are systematically investigated. The DFT+U-scf shows that VCl3 and VI3 monolayers have intrinsic ferromagnetism and half-metallicity. Remarkably, the VCl3 and VI3 monolayers possess a rather rare half-metallic Dirac point around the Fermi level with just one spin channel. In contrast to the Dirac point in graphene, the Dirac points in VCl3 and VI3 monolayers are mainly due to the V-d electrons and consequently they show a large spin-orbital coupling induced gaps of about 29 meV and 12 meV for VCl3 and VI3 monolayers, respectively. The Monte Carlo simulations based on the Ising model demonstrate that the Curie temperatures of VCl3 and VI3 sheets are only 80 K and 98 K, respectively. However, the Curie temperature can be increased up to room temperature by carrier doping. The feasibility of an exfoliation from VCl3 and VI3 layered bulk phases is confirmed due to the small cleavage energies. Our results greatly broaden the family of potential 2D Dirac materials. The calculated properties of VCl3 and VI3 monolayers show that these materials have great application potential, opening the way towards the development of high-performance electronic devices.