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Spin-Transfer Torques in One-Dimensional Magnetic Tunneling Junctions of Lateral Structures

Recent study in [C. C. Lin, Y. F. Gao, A. V. Penumatcha, V. Q. Diep, J. Appenzeller and Z. H. Chen, Acs Nano 8, 3807 (2014)], showed that the spin-transfer torque (STT) is enhanced by the asymmetry in a graphene lateral spin-valve structure. This lateral structure or geometry can be modeled by a four-terminal magnetic tunneling junction (MTJ) as opposite to the conventional two-terminal MTJ. In this paper, using the nonequilibrium Green’s function formalism (NEGF), we compare the anti-damping components of the STT in a similar nonconventional lateral one-dimensional MTJ with that in the conventional MTJ. We find that the lateral geometry renders enhanced anti-damping torques compared with the conventional one, provided that the barrier energy, the scattering length and the magnetization angle are in a certain parameter region. We also identify this parameter region in the presence of dephasing. The enhancement of the anti-damping torques declines when the scattering region is longer. For the four-terminal MTJ of larger scattering length, the dephasing can expedite the anti-damping torque.