Dynamic exchange coupling and Gilbert damping in magnetic multilayers

TL;DR

This paper provides a theoretical analysis of how dynamic exchange coupling and Gilbert damping in magnetic multilayers are influenced by spin currents and relaxation processes, explaining experimental observations in ultrathin magnetic films.

Contribution

It introduces a comprehensive theoretical framework for understanding spin-current-induced damping and exchange interactions in magnetic multilayers, aligning with recent experimental results.

Findings

Spin currents cause enhanced damping in ferromagnetic films.

Long-range dynamic exchange interactions are mediated by nonequilibrium spins.

Predictions match recent ferromagnetic-resonance experimental data.

Abstract

We theoretically study dynamic properties of thin ferromagnetic films in contact with normal metals. Moving magnetizations cause a flow of spins into adjacent conductors, which relax by spin flip, scatter back into the ferromagnet, or are absorbed by another ferromagnet. Relaxation of spins outside the moving magnetization enhances the overall damping of the magnetization dynamics in accordance with the Gilbert phenomenology. Transfer of spins between different ferromagnets by these nonequilibrium spin currents leads to a long-ranged dynamic exchange interaction and novel collective excitation modes. Our predictions agree well with recent ferromagnetic-resonance experiments on ultrathin magnetic films.