  We study spin and valley transports in junctions composed of silicene and
topological crystalline insulators. We consider normal/magnetic/normal Dirac
metal junctions where a gate electrode is attached to the magnetic region. In
normal/antiferromagnetic/normal silicene junction, we show that the current
through this junction is valley and spin polarized due to the coupling between
valley and spin degrees of freedom, and the valley and spin polarizations can
be tuned by local application of a gate voltage. In particular, we find a fully
valley and spin polarized current by applying the electric field. In
normal/ferromagnetic/normal topological crystalline insulator junction with a
strain induced in the ferromagnetic segment, we investigate valley resolved
conductances and clarify how the valley polarization stemming from the strain
and exchange field appears in this junction. It is found that changing the
direction of the magnetization and the potential in the ferromagnetic region,
one can control the dominant valley contribution out of four valley degrees of
freedom. We also review spin transport in normal/ferromagnetic/normal graphene
junctions, and spin and valley transports in normal/ferromagnetic/normal
silicene junctions for comparison.
