Multifunctional heterojunction and homojunction with nearly type-II spin gapless semiconductor FeVTaAl

Spin gapless semiconductors (SGSs), as the bridge between half-metals and semiconductors, have been regarded as the promising candidates for resolving the conductivity mismatch between magnetic half-metal layer and non-magnetic semiconductor layer in magnetic tunnel junctions. In particular, the type-II SGSs can achieve fully spin-polarized current with reversible spin polarization under a small gate voltage. Herein, based on the nearly type-II SGS of FeVTaAl Heusler alloy with a high Curie temperature of 681 K, we use fist-principles and non equilibrium Green's function method to investigate the spin-dependent transport properties of the FeVTaAl homojunction and the FeVTaAl/MgO heterojunction under bias voltage, temperature gradient and illumination. Distinct tunnel magnetoresistance and negative differential resistance behaviors are observed in the heterojunction, whereas the homojunction is found to exhibit pronounced spin-dependent Seebeck effect and spin photodiode effect. The pure spin photocurrent (spin battery) and fully spin polarized photocurrent can be achieved by tuning the photon energy or polarization angle of the incident light. These multifunctional transport characteristics are explained from the spin-dependent band structure, transmission spectrum in both energy and moment spaces, Fermi-Dirac distribution, and transmission trajectories. These findings indicate that FeVTaAl holds considerable potential for multifunctional applications in spintronics, spin caloritronics and spin optoelectronics, and will stimulate extensive studies on type-II SGSs.