▎ 摘　　要

We model a very large, tunable magnetoresistance (MR) in a graphene nanoribbon field-effect transistor, without artificial engineering of ferromagnetic contacts. A high MR of nearly 100% (about 50%) is obtained at low temperature (room temperature). We show that the MR ratio can be further tuned by using conventional electric field, in agreement with a recent experiment. The simulation results indicate that the large MR of GNRs stems from reduction of the bandgap of GNRs in the presence of applied magnetic field related to the 0th Landau level in graphene. Interestingly, in a more realistic device with edge roughness, the MR ratio is not degraded but rather enhanced, caused by the magnetic field induced spatial separation of the transport states. The large, tunable MR of GNRs resistant to edge roughness is attractive to device applications.