Exploring Weak Turbulence of Phonon and Magnon Beams in Magneto-Acoustic Ultrathin Films

TL;DR

This paper develops a simple theoretical model for weak turbulence involving phonon and magnon beams in ultrathin ferromagnetic films, explaining experimental observations and highlighting energy loss mechanisms.

Contribution

It introduces a novel simplified model for magnetoacoustic wave interactions in ultrathin films, incorporating nonlinear effects and providing predictive insights.

Findings

Linear envelope simulations match experimental angular dependence.

Enhanced magnetoacoustic coupling increases energy losses.

Model simplifies calculations of quasiparticle beam interactions.

Abstract

This study presents a simple theoretical model describing narrow envelope surface acoustic waves (phonons) and spin waves (magnons) in an ultrathin ferromagnetic film. Based on the general principles of weak wave turbulence, the model considers interactions between beams of an ideal phonon gas and a weakly non-ideal magnon gas, which represent magnetoacoustic oscillations in the system. Equations for the wave envelopes of phonons and magnons, along with their harmonics, are derived, incorporating nonlinear effects from three- and four-particle interactions. In the general non-resonant case, linear stationary envelope simulations are sufficient. These clarify the experimentally observed angular dependence of the transmitted acoustic signal with respect to the orientation of the magnetic field. The study highlights increased energy losses associated with enhanced magnetoacoustic coupling. Given the broad interdisciplinary interest in weak turbulence phenomena within condensed matter physics and nonlinear wave dynamics, our model offers significant predictive capabilities and greatly simplifies calculations of quasiparticle beam interactions.