Theory of spin transfer phenomena in magnetic metals and semiconductors

Abstract

Spin-transfer refers to the transfer of spin angular momentum between transport quasiparticles and the magnetic condensate of a ferromagnetic metal. It is ususally regarded as a consequence of total spin conservation. We discuss a theory that views spin-transfer from a more microscopic point of view and sees it as an example of a more general class of phenomena that occurs in any magnetic metal or semiconductor, and indeed in any system in which interactions contribute importantly to the quasiparticle self-energy. Our theory of spin transfer in ferromagnets does not rest on an appeal to conservation of total spin, can assess whether or not current-induced magnetization precession and switching in a particular geometry will occur coherently, and can estimate the efficacy of spin-transfer when spin-orbit interactions are present. We illustrate our theory by applying it to a toy-model two-dimensional-electron-gas ferromagnet with Rashba spin-orbit interactions and mention examples of related phenomena in other systems, most of which have not yet been realized experimentally.