▎ 摘　　要

We provide ab initio study on a spin valve device that is based on bare ferromagnetic zigzag-edged graphene nanoribbons. Giant magnetoresistance over one billion percent at room temperature is obtained, which is an ultrahigh magnetoresistance among graphene-related spin valve devices and seven orders of magnitude larger than the available experimental values. The orbital parity mismatching between the sigma and pi* bands and enhanced exchange splitting due to the dangling bond are two indispensable factors to generate this large magnetoresistance.