Computational search for two-dimensional intrinsic half-metals in transition-metal dinitrides

For next-generation nanospintronic devices, it is crucial to develop intrinsic half-metallic nanomaterials with a robust ferromagnetic (FM) ground state. Here, two kinds of two-dimensional (2D) intrinsic FM half-metals (HMs), i.e., p-state HMs (1T-TaN2 and 1T-NbN2) and d-state HM (1T-MnN2), have been characterized by a first-principles computational search of thirty possible structures of transition-metal (TM) dinitride monolayers, a new emerging class of 2D materials. Our comprehensive calculations of stability and magnetic properties show that the octahedral coordinated 1T-TaN2 monolayer is not only dynamically, thermally (500 K) and mechanically stable, but also possesses a robust FM ground state with a Curie temperature of similar to 339 K due to the strong N-N direct exchange interaction. Moreover, its half-metallic gap of 0.72 eV obtained from the HSE06 method is large enough to efficiently prevent the thermally agitated spin-flip transition. Unlike the reported 2D half-metallic TM compounds, the half-metallicity and magnetic moments of 1T-TaN2 are mainly attributed to the p orbitals of non-metal atoms (N) instead of d orbitals of TM atoms (T-a), which are beneficial for overcoming the issue of the short spin-relaxation-time caused by large spin coupling of TM atoms. Based on these results, it is reasonable to believe that the selected 1T-TaN2 monolayer is one of the most promising 2D materials for nanospintronic applications.