  We study spin transport in normal/ferromagnetic/normal graphene junctions
where a gate electrode is attached to the ferromagnetic graphene. We find that
due to the exchange field of the ferromagnetic graphene, spin current through
the junctions has an oscillatory behavior with respect to the chemical
potential in the ferromagnetic graphene, which can be tuned by the gate
voltage. Especially, we obtain a controllable spin current reversal by the gate
voltage. Our prediction of high controllability of spin transport in
ferromagnetic graphene junction may contribute to the development of the
spintronics.
