Magnetization dynamics affected by phonon pumping

TL;DR

This study investigates how phonon pumping influences ferromagnetic resonance spectra in YIG/GGG bilayers, revealing mode hybridization, increased line width at higher frequencies, and significant magnon-phonon coupling, advancing magnonic device control.

Contribution

It demonstrates the impact of phonon pumping on FMR spectra, highlighting mode hybridization and coupling effects, with implications for engineering magnetoelastic interactions.

Findings

Hybridization of Kittel mode with ultrasound waves forms magnon polarons.

Increased FMR line width correlates with phonon resonance overlap.

Substantial magnon-phonon coupling observed in PSSW mode.

Abstract

"Pumping" of phonons by a dynamic magnetization promises to extend the range and functionality of magnonic devices. We explore the impact of phonon pumping on room-temperature ferromagnetic resonance (FMR) spectra of bilayers of thin yttrium iron garnet (YIG) films on thick gadolinium gallium garnet substrates over a wide frequency range. At low frequencies the Kittel mode hybridizes coherently with standing ultrasound waves of a bulk acoustic resonator to form magnon polarons that induce rapid oscillations of the magnetic susceptibility, as reported before. At higher frequencies, the phonon resonances overlap, merging into a conventional FMR line, but with an increased line width. The frequency dependence of the increased line broadening follows the predictions from phonon pumping theory in the thick substrate limit. In addition, we find substantial magnon-phonon coupling of a perpendicular standing spin wave (PSSW) mode. This evidences the importance of the mode overlap between the acoustic and magnetic modes, and provides a route towards engineering the magnetoelastic mode coupling.