▎ 摘　　要

The spin filter effect and magnetoresistance (MR) in the graphene nanoribbons with zigzag edges have been investigated by the non-equilibrium Green's function method. Due to the spin-dependent current blocking effect, the ferromagnetic graphene/normal graphene junction can filter the spin in one direction, so a fully spin-polarized current is found. As the on-site energy mu(R) in the right lead goes from negative to positive, the spin-down transmission would suddenly transforms from an `ON' state to an `OFF' state, however the spin-up transmission transforms from an `OFF' state to an `ON' state, so we can choose the current's spin polarized direction by tuning mu(R). For the ferromagnetic graphene/ferromagnetic graphene junction the current for the antiparallel magnetization configuration is blocked, a very large MR is obtained. It is expected that these features may serve as a type of useful spintronic devices in future.