The introduction of a strong Rashba spin orbit coupling (SOC) had been predicted to enhance the spin motive force (SMF) [see Phys. Rev. Lett. {bf 108}, 217202 (2012)]. In this work, we predict further enhancement of the SMF by time modulation of the
Rashba coupling $alpha_R$, which induces an additional electric field $E^R_d={dot alpha_R} m_e/ehbar({hat z}times {mathbf m})$. When the modulation frequency is higher than the magnetization precessing frequency, the amplitude of this field is significantly larger than previously predicted results. Correspondingly, the spin torque on the magnetization is also effectively enhanced. Additionally, the nature of SOC induced spin torque in the system can be transformed from damping to antidamping-like by modulating ${dot alpha_R}$. We also suggest a biasing scheme to achieve rectification of SMF, {it i.e.}, by application of a square wave voltage at the resonant frequency. Finally, we numerically estimate the resulting spin torque field arising from a Gaussian pulse time modulation of $alpha_R$.
We investigate the spin Hall effect (SHE) in a wide class of spin-orbit coupling systems by using spin force picture. We derive the general relation equation between spin force and spin current and show that the longitudinal force component can induc
e a spin Hall current, from which we reproduce the spin Hall conductivity obtained previously using Kubos formula. This simple spin force picture gives a clear and intuitive explanation for SHE.
