  We investigate charge conductance and spin and valley polarization along with
the tunnelling magneto-resistance (TMR) in silicene junctions composed of
normal silicene and ferromagnetic silicene. We show distinct features of the
conductances for parallel and anti-parallel spin configurations and the TMR, as
the ferromagnetic-normal-ferromagnetic (FNF) junction is tuned by an external
electric field. We analyse 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 structure at the two valleys are independently affected by
the spin in the ferromagnetic regions and lead to non-zero, 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.
