Spin-Transfer Torque and Electron-Magnon Scattering

TL;DR

This paper reexamines the mechanisms behind current-driven magnetic dynamics in ferromagnetic multilayers, highlighting the significance of electron spins parallel to the field and introducing quantum-mechanical aspects of spin-transfer.

Contribution

It challenges the conventional spin-torque model by emphasizing the role of electron spins parallel to the field and discusses quantum effects not captured by traditional models.

Findings

Electron spin parallel to the field dominates magnetic dynamics.

Spin-transfer can be viewed as stimulated excitation of spin-waves.

Four quantum-mechanical aspects of spin-transfer are identified.

Abstract

According to the spin-torque model, current-driven magnetic dynamics in ferromagnetic multilayers is determined by the transfer of electron spin perpendicular to the layers' magnetizations. By separating the largest contributions to the magnetic dynamics, we demonstrate that the dominant effect of spin-torque is rather due to the electron spin parallel to the field. We show that this effect can be equivalently described as stimulated current-driven excitation of spin-waves, and discuss four specifically quantum-mechanical aspects of spin-transfer, not described by the spin-torque.