Room-temperature giant magnetoresistance over one billion percent in a bare graphene nanoribbon device

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 $\ensuremath{\sigma}$ and ${\ensuremath{\pi}}^{\ensuremath{\ast}}$ bands and enhanced exchange splitting due to the dangling bond are two indispensable factors to generate this large magnetoresistance.