First-principles prediction of magnetically ordered half-metals above room temperature

Half-metallicity (HM) offers great potential for engineering spintronic applications, yet only few magnetic materials present metallicity in just one spin channel. In addition, most HM systems become magnetically disordered at temperatures well below ambient conditions, which further hinders the development of spin-based electronic devices. Here, we use first-principles methods based on density functional theory (DFT) to investigate the electronic, magnetic, structural, mixing, and vibrational properties of 90 XYZ half-Heusler (HH) alloys (X= Li, Na, K, Rb, Cs; Y= V, Nb, Ta; Z= Si, Ge, Sn, S, Se, Te). We disclose a total of 28 new HH compounds that are ferromagnetic, vibrationally stable, and HM, with semiconductor band gaps in the range of 1–4 eV and HM band gaps of 0.2–0.8 eV. By performing Monte Carlo simulations of a spin Heisenberg model fitted to DFT energies, we estimate the Curie temperature, T_C, of each HM compound. We find that 17 HH HM remain magnetically ordered at and above room temperature, namely, 300≤T_C≤450 K, with total magnetic moments of 2 and 4 μ_B. A further materials sieve based on zero-temperature mixing energies let us to conclude 5 overall promising HH HM that remain magnetically ordered at and above room temperature: NaVSi, RbVTe, CsVS, CsVSe, and RbNbTe. We also predict 2 semiconductor materials that are ferromagnetic at ambient conditions: LiVSi and LiVGe.