Spin-pumping and Enhanced Gilbert Damping in Thin Magnetic Insulator Films

TL;DR

This paper develops a theoretical model to understand how spin-pumping affects Gilbert damping in thin magnetic insulator films, revealing mode-dependent enhancements and aligning with experimental data.

Contribution

It introduces a quantitative theory for spin-pumping dependence on mode number and wave vector, clarifying the damping enhancement in different spin wave modes.

Findings

Enhanced damping is twice for transverse volume modes compared to macrospin.

Surface modes can have ten or more times damping enhancement.

Spin-pumping is negligible for short-wavelength exchange spin waves.

Abstract

Precessing magnetization in a thin film magnetic insulator pumps spins into adjacent metals; however, this phenomenon is not quantitatively understood. We present a theory for the dependence of spin-pumping on the transverse mode number and in-plane wave vector. For long-wavelength spin waves, the enhanced Gilbert damping for the transverse mode volume waves is twice that of the macrospin mode, and for surface modes, the enhancement can be ten or more times stronger. Spin-pumping is negligible for short-wavelength exchange spin waves. We corroborate our analytical theory with numerical calculations in agreement with recent experimental results.