The mechanical back-action of a spin-wave resonance in a magnetoelastic thin film on a surface acoustic wave

TL;DR

This paper develops a perturbation theory to analyze how spin-wave resonance in a magnetoelastic film affects surface acoustic wave propagation, revealing back-action effects like velocity shifts, attenuation, and surface currents.

Contribution

It introduces a novel perturbative approach to quantify the back-action of spin-wave resonance on SAWs, differing from previous polariton-based models.

Findings

Derived closed-form expressions for SAW velocity shifts and attenuation.

Identified surface currents generated by spin-wave back-action.

Applicable to experimental regimes with first-order perturbations.

Abstract

Surface acoustic waves (SAWs) traveling on the surface of a piezoelectric crystal can, through the magnetoelastic interaction, excite traveling spin-wave resonance in a magnetic film deposited on the substrate. This spin-wave resonance in the magnetic film creates a time dynamic surface stress of magnetoelastic origin that acts back on the surface of the piezoelectric and modifies the SAW propagation. Unlike previous analyses that treat the excitation as a magnon-phonon polariton, here the magnetoelastic film is treated as a perturbation modifying boundary conditions on the SAW. We use acoustical perturbation theory to find closed form expressions for the back-action surface stress and strain fields and the resultant SAW velocity shifts and attenuation. We demonstrate that the shear stress fields associated with this spin-wave back-action also generate effective surface currents on the piezoelectric both in-phase and out-of-phase with the driving SAW potential. Characterization of these surface currents and their applications in determination of the magnetoelastic coupling are discussed. The perturbative calculation is carried out explicitly to first order (a regime corresponding to many experimental situations of current interest) and we provide a sketch of the implications of the theory at higher order.