  We theoretically demonstrate a simple way to significantly enhance the
spin/valley polarizations and tunnel- ing magnetoresistnace (TMR) in a
ferromagnetic-normal-ferromagnetic (FNF) silicene junction by applying a
circularly polarized light in 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 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 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 FNF silicene junction, especially in
spintronics.
