Gate-control of spin-motive force and spin-torque in Rashba SOC systems

TL;DR

This paper predicts that time modulation of Rashba spin-orbit coupling can significantly enhance spin-motive force and spin torque, enabling control and rectification in spintronic systems.

Contribution

It introduces a novel method of enhancing and controlling spin-motive force and spin torque via dynamic Rashba coupling modulation, including a rectification scheme.

Findings

Enhanced spin-motive force with high-frequency modulation

Transformation of spin torque from damping to antidamping-like

Numerical estimation of spin torque from Gaussian pulse modulation

Abstract

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 $E^R_d={\dot \alpha_R} m_e/e\hbar({\hat z}\times {\mathbf m})$. 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 $\alpha_R$.