Micromagnetic simulations of persistent oscillatory modes excited by spin-polarized current in nanoscale exchange-biased spin valves

TL;DR

This study uses advanced 3D micromagnetic simulations to explore how thermal effects, damping, and back action influence persistent oscillations in nanoscale spin valves driven by spin-polarized currents, aligning theory with experiments.

Contribution

It introduces comprehensive 3D micromagnetic simulations that incorporate back action, non-linear damping, and thermal effects to better understand current-driven magnetization dynamics.

Findings

Thermal and spin transfer torques induce multi-mode oscillations.

Simulations show nonstationary behavior at sub-critical currents.

Results align better with experimental observations.

Abstract

We perform 3D micromagnetic simulations of current-driven magnetization dynamics in nanoscale exchange biased spin-valves that take account of (i) back action of spin-transfer torque on the pinned layer, (ii) non-linear damping and (iii) random thermal torques. Our simulations demonstrate that all these factors significantly impact the current-driven dynamics and lead to a better agreement between theoretical predictions and experimental results. In particular, we observe that, at a non-zero temperature and a sub-critical current, the magnetization dynamics exhibits nonstationary behaviour in which two independent persistent oscillatory modes are excited which compete for the angular momentum supplied by spin-polarized current. Our results show that this multi-mode behaviour can be induced by combined action of thermal and spin transfer torques.