Photoenhanced spin/valley polarization and tunneling magnetoresistance in a ferromagnetic-normal-ferromagnetic silicene junction

We theoretically demonstrate a simple way to significantly enhance the spin/valley polarizations and tunneling magnetoresistnace (TMR) in a ferromagnetic-normal-ferromagnetic (FNF) silicene junction by applying a circularly polarized light in the off-resonant regime to the second ferromagnetic (FM) region. We show that the fully spin-polarized current can be realized in certain ranges of light intensity. Increasing the incident energy in the presence of light will induce a transition of perfect spin polarization from positive to negative or vice versa depending on the magnetic configuration (parallel or anti-parallel) of FNF junction. Additionally, under a circularly polarized light, valley polarization is very sensitive to electric field and the perfect valley polarization can be achieved even when staggered electric field is much smaller than exchange field. The most important result we would like to emphasize in this paper is that the perfect spin polarization and 100% TMR induced by a circularly polarized light are completely independent of barrier height in the normal region. Furthermore, the sign reversal of TMR can be observed when the polarized direction of light is changed. A condition for observing the 100% TMR is also reported. Our results are expected to be informative for real applications of a FNF silicene junction, especially in spintronics. (paper)