Investigation of the half-metallicity, magnetism and spin transport properties of double half-Heusler alloys Mn2CoCrZ2 (Z = P, As)

A new subfamily of Heusler alloys, i.e. double half-Heusler alloys Mn(2)CoCrZ(2) (Z = P, As), are investigated by employing density functional theory combined with the nonequilibrium Green's function. The calculations of their magnetic properties reveal that Mn(2)CoCrZ(2) (Z = P, As) are half-metallic ferrimagnets. Mn2CoCrP2 possesses an indirect spin-down bandgap of 0.671 eV and maintains half-metallicity with the lattice constant ratio c/a ranging from 1.72 to 2.40, while Mn2CoCrAs2 owns a direct spin-down bandgap of 0.993 eV and maintains half-metallicity with c/a ranging from 1.5 to 2.5. By employing Mn(2)CoCrZ(2) as the electrodes and GaAs as the tunnel barrier, two kinds of magnetic tunnel junctions (MTJs) are constructed. When two electrodes of MTJs are in parallel magnetic configuration, the spin-up electrons have strong transmission ability, while the transmission ability of spin-down electrons is severely suppressed. When two electrodes of MTJs are in antiparallel magnetic configuration, the transmission ability of both spin-channel electrons is suppressed. The calculated tunnel magnetoresistance ratios of Mn2CoCrP2/GaAs/Mn2CoCrP2 and Mn2CoCrAs2/GaAs/Mn2CoCrAs2 MTJs reach up to 7.96 x 10(8) and 1.85 x 10(8), respectively, indicating that they are promising candidates for high performance spintronic devices.