Department of Physics and Key Laboratory for Low-Dimensional Quantum Structures and Manipulation (Ministry of Education), Hunan Normal University, Changsha, People's Republic of China.
J Phys Condens Matter. 2010 Nov 10;22(44):445302. doi: 10.1088/0953-8984/22/44/445302. Epub 2010 Oct 22.
We theoretically investigate the spin-dependent transport through a graphene sheet between two ferromagnetic (FM) leads with arbitrary polarization directions at low temperatures, where a magnetic insulator is deposited on the graphene to induce an exchange splitting between spin-up and spin-down carriers. By using standard nonequilibrium Green's function (NGF) techniques, it is demonstrated that the density of states (DOS) decreases for spin-up and increases for spin-down when the polarization strength of the two leads in parallel alignment increases. For the electron energy around the exchange splitting, the DOS for both spin-up and spin-down channels is independent of the polarization. In contrast, the conductance increases for spin-up but decreases for spin-down with an increase of the polarization. Interestingly, the magnitude of tunneling magnetoresistance (TMR) can be dramatically suppressed with the increase of the exchange splitting in graphene. Furthermore, the current-induced spin transfer torque (STT) dependence on the relative angle θ between the magnetic moments of the two leads shows a sine-like behavior and is enhanced with an increase of the polarization and/or the bias voltage. We attribute these spin-resolved effects to the breaking of the insulator-type properties of graphene with an exchange splitting between spin-up and spin-down carriers.
我们从理论上研究了低温下两个具有任意极化方向的铁磁（FM）引线之间通过石墨烯片的自旋相关输运，其中在石墨烯上沉积了一个磁绝缘体，以在自旋向上和自旋向下载流子之间诱导交换劈裂。通过使用标准的非平衡格林函数（NGF）技术，我们证明了当两个平行对齐的引线的极化强度增加时，自旋向上的态密度（DOS）减小，而自旋向下的态密度增加。对于交换劈裂附近的电子能量，自旋向上和自旋向下通道的 DOS 与极化无关。相比之下，随着极化的增加，自旋向上的电导增加，而自旋向下的电导减小。有趣的是，随着石墨烯中交换劈裂的增加，隧穿磁电阻（TMR）的幅度可以显著抑制。此外，电流诱导的自旋转移扭矩（STT）对两个引线的磁矩之间的相对角度θ的依赖性表现出类似正弦的行为，并随着极化和/或偏压的增加而增强。我们将这些自旋分辨效应归因于具有自旋向上和自旋向下载流子之间交换劈裂的石墨烯的绝缘型特性的破坏。
