Interaction Of Electrons With Spin Waves In The Bulk And In Multilayers

TL;DR

This paper reviews the theory and experiments on how electrons interact with spin waves in magnetic multilayers, highlighting interface effects and current-induced spin torques relevant for spintronic applications.

Contribution

It provides a comprehensive analysis of the enhanced exchange interaction at interfaces and how dc currents can generate spin oscillations in multilayer structures.

Findings

Interface proximity restores spin torque within 10 nm.

Spin current and spin imbalance are proportional and can originate from Fermi-surface shifts.

Current-induced spin torque can be calculated from spin current or spin imbalance.

Abstract

The exchange interaction between electrons and magnetic spins is considerably enhanced near interfaces, in magnetic multilayers. As a result, a dc current can be used to generate spin oscillations. We review theory and experimental evidence. The s-d exchange interaction causes a rapid precession of itinerant conduction-electron spins s around the localized spins S of magnetic electrons. Because of the precession, the time-averaged interaction torque between s and S vanishes. An interface between a magnetic layer and a spacer causes a local coherence between the precession phases of differnt electrons, within 10 nm from the interface, and restores the torque. Also, a second magnetic layer with pinned S is used to prepare s in a specific direction. the current-induced drive torque of s on S in the active layer may be calculated from the spin current (Slonczewski) or from the spin imbalance Delta-mu (Berger). Spin current and Delta-mu are proportional to each other, and can arise from Fermi-surface translation, as well as from expansion/contraction.