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High spin-injection-efficiency (SIE) and thermal spin-filter-effect (SFE) from a magnetic material to a barrier material are crucial to the high performance of a spintronic device and a spin caloritronic device, respectively. By performing a nonequilibrium Green's function combined with first-principles calculations, we study the voltage-driven and temperature-driven spin transport properties of a half Heusler alloy RuCrAs based spin valve with different atom-terminated interfaces. The spin valve with a CrAs-top (or Ru-top) interface structure has an ultrahigh equilibrium magnetoresistance (MR) ratio of ∼1.56 × 109% (or ∼5.14 × 108%), ∼100% SIE, a large MR ratio, and high spin current intensity under bias voltage, suggesting that it has a great potential application in spintronic devices. The spin valve with the CrAs-top (or CrAs-bri) interface structure has a perfect SFE due to its very high spin polarization of temperature-driven currents, and it is useful in spin caloritronic devices. [ABSTRACT FROM AUTHOR]

A highly lattice-matched all-Heusler-alloy magnetic tunnel junction (MTJ) is proposed by associating half metallic CoFeTiSi electrode and non-magnetic semiconductor Fe2TiSi barrier. Based on the non-equilibrium Green's function combined with first-principles calculations, spin transport mechanism is studied by analyzing the transmission coefficient, local density of states, and scattering states. The calculated equilibrium tunnel magnetoresistance (TMR) ratio in CoFeTiSi/Fe2TiSi/CoFeTiSi reaches up to about 3.30 × 108%, which is much higher than in CoFeTiSi/MgO/CoFeTiSi. The calculated scattering states reveal that CoFeTiSi/Fe2TiSi/CoFeTiSi MTJ possesses two transport channels, and the contribution of channel I to the total transport is about 80%, which plays a dominate role. The analyses on non-equilibrium spin transport properties reveal that CoFeTiSi/MgO/CoFeTiSi MTJ can output a high intensity transport current with complete spin polarization, and it can output a stable and highly efficient signal. The TMR ratio possesses an extremely large value of about 2.4 × 108% and even the bias voltage increases to 0.2 V, exhibiting a robust current-driven stability. [ABSTRACT FROM AUTHOR]

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. Mn 2 CoCrP 2 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 Mn 2 CoCrAs 2 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 Mn 2 CoCrP 2 /GaAs/Mn 2 CoCrP 2 and Mn 2 CoCrAs 2 /GaAs/Mn 2 CoCrAs 2 MTJs reach up to 7.96 × 10 8 and 1.85 × 10 8 , respectively, indicating that they are promising candidates for high performance spintronic devices.