Spin-dependent transport and current-induced spin transfer torque in a strained graphene spin valve

Kai-He Ding,1,* Zhen-Gang Zhu,2,3,† and Gang Su2,‡

1Department of Physics and Electronic Science, Changsha University of Science and Technology, Changsha 410076, China 2Theoretical Condensed Matter Physics and Computational Materials Physics Laboratory, School of Physics, University of Chinese Academy of Science, Beijing 100049, China 3School of Electronic, Electrical and Communication Engineering, University of Chinese Academy of Sciences, Beijing 100049, China

Using the nonequilibrium Green’s function method, we investigated theoretically the spin-dependent transport and the current-induced spin transfer torque (CISTT) in a zigzag-graphene-nanoribbon (ZGNR) spin valve in the presence of an applied uniaxial strain to the ZGNR. It is found that, when a longitudinal or transverse strain is applied, the conductance versus the Fermi energy remains unchanged around the Dirac point. However, when the Fermi energy is larger than the molecular field of two ferromagnetic electrodes, the dependence of the conductance on the uniaxial strain exhibits totally different behaviors for parallel and antiparallel configurations for the electrodes’ magnetizations, which leads to a transition of magnetoresistance (MR) from a perfect histogramlike behavior to successive cusplike peaks and to a steplike behavior with sharp peaks for the longitudinal and transverse strains, respectively. It is further shown that the CISTT per unit of the bias voltage as a function of the Fermi energy is antisymmetric respective to the Dirac point and exhibits typical successive oscillations composed of broad peaks closely followed by sharp ones.