Robust half-metallicity in transition metal tribromide nanowires

Abstract

One-dimensional (1D) nanowires (NWs) with robust half-metallicity are a rising star in spintronics. Herein, we theoretically investigate the magnetic and electronic properties of 3d transition-metal tribromide NWs, i.e. TMBr₃ (TM = Sc, Ti, V, Cr, Co, and Cu). These systems represent repeated TMBr₃ motifs with octahedral configuration, and are expected to be synthesized in a nanotube using an established method. Among these NWs, both VBr₃ and CuBr₃ NWs exhibit a ferromagnetic (FM) ground state, accompanied by sizable magnetocrystalline anisotropic energy, which is dominated by the superexchange coupling between the TM atoms. Strikingly, a half-metallic nature with a magnetic moment of 4.0μ_B per unit cell is predicted for the VBr₃ NW. By combining with a tight-binding model, we demonstrate that the origin behind the half-metallicity is the half-filled e₂ orbitals of the V atoms. The Curie temperature is evaluated to be up to 80 K using Monte Carlo simulations, which is comparable to the temperature of liquid nitrogen. We also find that the half-metallic behavior shows a favorable tolerance to the longitudinal elongation of the wire (∼10%). Additionally, a transition from FM semiconductor to half-metal can be realized in the CuBr₃ NW through carrier doping. The coexistence of intrinsic high-temperature FM ordering and half-metallicity endows 1D TMBr₃ NWs with great promise for spintronic and photoelectron device applications.