  We report on the possibility for a spin valve effect driven by edge defect
engineering of zigzag graphene nanoribbons. Based on a mean-field spin
unrestricted Hubbard model, electronic band structures and conductance profiles
are derived, using a self-consistent scheme to include gate-induced charge
density. The use of an external gate is found to trigger a semiconductor-metal
transition in clean zigzag graphene nanoribbons, whereas it yields a closure of
the spin-split bandgap in the presence of Klein edge defects. These features
could be exploited to make novel charge and spin based switches and field
effect devices.
