Prediction of Giant Spin Motive Force due to Rashba Spin-Orbit Coupling

Magnetization dynamics in a ferromagnet can induce a spin-dependent electric field through spin motive force. Spin current generated by the spin-dependent electric field can in turn modify the magnetization dynamics through spin-transfer torque. While this feedback effect is usually weak and thus ignored, we predict that in Rashba spin-orbit coupling systems with large Rashba parameter $\alpha_{\rm R}$, the coupling generates the spin-dependent electric field [$\pm(\alpha_{\rm R}m_e/e\hbar) (\vhat{z}\times \partial \vec{m}/\partial t)]$, which can be large enough to modify the magnetization dynamics significantly. This effect should be relevant for device applications based on ultrathin magnetic layers with strong Rashba spin-orbit coupling.