Electronic phase transition, spin filtering effect, and spin Seebeck effect in 2D high-spin-polarized VSi2X4 (X = N, P, As)

Spin gapless semiconductors (SGSs) and bipolar magnetic semiconductors (BMSs) are highly desirable for advanced spintronic applications due to their unique electronic and magnetic properties. Being inspired by the recent synthesis of the 2D MA2X4 family with various electronic properties, including nontrivial topological properties, 2D ferromagnetism, Ising superconductivity, and robust valley polarization, we systematically studied the electron structure, magnetism, and spin transport properties for VSi2X4 (X = N, P, As) monolayers by the density functional theory combined with the nonequilibrium Green's function method. The results show that VSi2X4 monolayers are ferromagnetic type-II SGS and BMS with high Curie temperatures 230–250 K. The interesting electronic phase transitions of type-II-SGS-to-metal-to-type-I-SGS for VSi2P4 and BMS-to-type-I-SGS-to-type-II-SGS for VSi2As4 can be achieved by applying the biaxial strain. Furthermore, the VSi2P4 monolayer exhibits the bias-dependent spin filtering effect and the temperature-driven spin Seebeck effect. The high Curie temperature, the versatile strain-tuned electronic phase transitions, and the excellent spin transport characteristics make 2D VSi2X4 the promising candidate for spintronic applications and will stimulate intensive studies on this class of high-spin-polarized 2D systems.