▎ 摘　　要

We propose a spin device based on a T-shaped graphene junction (TGJ) in which a ferromagnetic insulator and a metallic gate are deposited on the sidearm. Spin transport properties of the TGJ are studied by using the Green's function method. It is found that spin-polarized transport can be achieved both far away from and near the Dirac point. The spin polarization far away from the Dirac point is correlated with the quasi-bound states in the junction, while the spin polarization near the Dirac point is due to the destruction of edge states. By varying the strength of the potential, i.e., the gate voltage on the sidearm, the spin polarization can be tuned quasi-periodically from -100% to 100%. In addition, the size of the sidearm also shows obvious influence on the spin polarization of TGJ. (C) 2011 American Institute of Physics. [doi: 10.1063/1.3615951]