Valley controlled spin-transfer torque in ferromagnetic graphene junctions

The presence of the valley degree of freedom in graphene leads to the valleytronics, in which information is encoded by the valley quantum number of the electron. We propose a valley controlled spin-transfer torque (STT) in graphene-based normal/normal/ferromagnetic junctions with the normal lead irradiated by the off-resonant circularly polarized light. The interplay of the spin–orbit interaction and the staggered potential in the central normal part results in the coupling between the valley and spin degrees of freedom, so a valley dependent spin polarized current can be demonstrated, which can exert a valley controlled STT on the ferromagnetic lead. The amplitude of the STT can be manipulated by the intensity of the light, the Fermi energy and the magnetization direction of the ferromagnetic lead. This valley controlled STT may find potential application in future valleytronics and spintronics. (paper)