Theory of electron transport and magnetization dynamics in metallic ferromagnets

TL;DR

This paper develops a theoretical framework for understanding electron transport and magnetization dynamics in metallic ferromagnets using effective spin electromagnetic fields, revealing novel effects like spin motive force, topological Hall effect, and Rashba-induced phenomena.

Contribution

It introduces a comprehensive theory connecting spin gauge fields with magnetization dynamics, spin transport, and optical effects in ferromagnetic metals, including extensions to spin relaxation and Rashba interactions.

Findings

Spin Berry's phase leads to spin motive force and topological Hall effect.

Rashba spin-orbit interaction induces asymmetric light propagation and negative refraction.

Effective gauge fields explain voltage generation and directional dichroism phenomena.

Abstract

Magnetic electric effects in ferromagnetic metals are discussed from the viewpoint of effective spin electromagnetic field that couples to conduction electron spin. The effective field in the adiabatic limit is the spin Berry's phase in space and time, and it leads to spin motive force (voltage generated by magnetization dynamics) and topological Hall effect due to spin chirality. Its gauge coupling to spin current describes the spin transfer effect, where magnetization structure is driven by an applied spin current. The idea of effective gauge field can be extended to include spin relaxation and Rashba spin-orbit interaction. Voltage generation by the inverse Edelstein effect in junctions is interpreted as due to the electric component of Rashba-induced spin gauge field. The spin gauge field arising from the Rashba interaction turns out to coincides with troidal moment, and causes asymmetric light propagation (directional dichroism) as a result of the Doppler shift. Rashba conductor without magnetization is shown to be natural metamaterial exhibiting negative refraction.