Conductance, valley and spin polarizations, and tunneling magnetoresistance in ferromagnetic-normal-ferromagnetic junctions of silicene

We investigate charge conductance and spin and valley polarization along with the tunneling magnetoresistance (TMR) in silicene junctions composed of normal silicene and ferromagnetic silicene. We show distinct features of the conductances for parallel and antiparallel spin configurations and the TMR, as the ferromagnetic-normal-ferromagnetic junction is tuned by an external electric field. We analyze the behavior of the charge conductance and valley and spin polarizations in terms of the independent conductances of the different spins at the two valleys and the band structure of ferromagnetic silicene and show how the conductances are affected by the vanishing of the propagating states at one or the other valley. In particular, unlike in graphene, the band structures at the two valleys are independently affected by the spin in the ferromagnetic regions and lead to nonzero and, in certain parameter regimes, pure valley and spin polarizations, which can be tuned by the external electric field. We also investigate the oscillatory behavior of the TMR with respect to the strength of the barrier potential (both spin-independent and spin-dependent barriers) in the normal silicene region and note that in some parameter regimes, the TMR can even go from positive to negative values, as a function of the external electric field.