  We investigate spin transport through ferromagnetic graphene vertical
heterostructures where a sandwiched tunneling layer is either a normal or
ferroelectric insulator. We show that the spin-polarization of the tunneling
current is electronically controlled via gate voltages. We also demonstrate
that the tunneling current of Dirac fermions can be prohibited when the spin
configuration of ferromagnetic graphene sheets is opposite. The giant
electroresistance can thus be developed by using the proposed heterostructure
in this study. The effects of temperature on the spin transport and the giant
electroresistance ratio are also investigated. Our findings discover the
prospect of manipulating the spin transport properties in vertical
heterostructures through an electric fields via gate and bias electrodes.
