Nonequilibrium dynamics in a spin valve with noncollinear magnetization

TL;DR

This paper investigates the complex spin dynamics and transfer torques in a noncollinear spin valve under bias, revealing how bias voltage influences relaxation times and induces resonant behaviors in spin systems.

Contribution

It introduces a hybrid quantum-classical approach to analyze spin-transfer effects and uncovers the impact of bias voltage on relaxation times and resonance phenomena in spin valves.

Findings

Bias voltage significantly affects spin relaxation times.

Resonant features occur when lead chemical potentials align with electronic density maxima.

Symmetric and asymmetric voltages cause relaxation time differences by orders of magnitude.

Abstract

We utilize a hybrid quantum-classical equation of motion approach to investigate the spin dynamics and spin-transfer torque in a spin valve under bias voltage. We show that the interplay between localized classical magnetic moments and conduction electrons induces a complex effective exchange coupling between the magnetic layers. This leads to a declination of magnetizations from layers anisotropy axes even in equilibrium. Introducing a finite bias voltage triggers spin currents and related spin-transfer torques which further tilt the magnetizations and govern the relaxation processes of the spin dynamics. Analyzing different scenarios of the applied bias voltage, we show that symmetric and asymmetric voltage drops can lead to relaxation times of the spin dynamics that differ by several orders of magnitude at comparable charge currents. In both cases we observe resonant features, where the relaxation is boosted whenever the chemical potential of the leads matches the maxima in the density of the states of the spin-valve electrons.