Dynamic stiffness of spin valves

TL;DR

This paper investigates how nonequilibrium spin-current exchange influences magnetization dynamics in spin valves, revealing a critical current bias for coherent excitation and a configuration-dependent damping effect.

Contribution

It introduces a unified framework for understanding spin-current effects on magnetization dynamics, extending previous models by incorporating nonequilibrium exchange interactions.

Findings

Identifies a low-temperature critical current bias for coherent magnetization excitation.

Shows spin transfer effects can be represented as magnetic-configuration-dependent Gilbert damping.

Unifies previous theories of spin-transfer torque in spin valves.

Abstract

The dynamics of the magnetic order parameters of ferromagnet/normal-metal/ferromagnet spin valves and isolated ferromagnets may be very different. We investigate the role of the nonequilibrium spin-current exchange between the ferromagnets in the magnetization precession and switching. We find a (low-temperature) critical current bias for a coherent current-induced magnetization excitation in spin valves, which unifies and generalizes previous ideas of Slonczewski and Berger. In the absence of an applied bias, the effect of the spin transfer can be expressed as magnetic--configuration-dependent Gilbert damping.