▎ 摘　　要

We calculate the electric conductance of a graphene nanoribbon (GNR) with and without a point defect. In the case of a zigzag GNR, magnetic moments are formed near the zigzag edges, and the electric current on each edge is spin-polarized. By breaking the symmetry of the magnetic moments with a single defect, such as a nonmagnetic vacancy, a net spin-polarized current can be generated in a zigzag GNR. The spatial distribution of the current is studied, and the spin-polarized current is found to arise owing to the blocking of a spin-polarized current-carrying mode by a vacancy.