Time- and space-resolved nonlinear magnetoacoustic dynamics

Abstract

Nonlinear magnetization dynamics are of great interest, being, for instance, leveraged for neuromorphic computing in spin-transfer torque nano-oscillators. Here, we demonstrate how to implement magnetoacoustics to reach this regime, using monochromatic (f saw = 450 MHz) surface acoustic waves traveling on a thin layer of (Ga,Mn)As. By careful tuning of the precession frequency to both f saw and 2 f saw using the magnetic field and temperature, we evidence clear signatures of a nonlinear magnetoacoustic response of the magnetic dynamics using the time-and space-resolved Kerr effect: (i) frequency and wave-vector doubling in time and space, respectively, (ii) quadratic (sublinear) evolution of the precession amplitude at 2 f saw (f saw) with acoustic amplitude, and (iii) resonance field shift. While (i) can be well reproduced by a parametric resonance model where nonlinearities arise solely from the SAW, we show that features (ii) and (iii) also involve intrinsic magnetic nonlinearities. Understanding the conditions leading to these nonlinearities will mean better control of the acoustic-wave-driven magnetization dynamics, in order to implement optimally the wave properties enabled by this approach.

The 2022 magneto-optics roadmap

“…Further theoretical analysis in high-frequency magnetoacoustics should help identifying the role of phase-matching conditions, magnetic and acoustic boundary conditions [137] in generating large-amplitude magnon precession in magnetostrictive materials. It is expected to facilitate the experimental studies targeting the magnon-assisted parametric [146] and nonlinear magnetoacoustic dynamics [147].…”

Resonant and Off-Resonant Magnetoacoustic Waves in Epitaxial Fe3Si/GaAs Hybrid Structures

“…The coupling between strain and magnetization-the magnetoelastic (ME) effect-can be used to generate magnetization dynamics at the nanoscale with low-power dissipation through surface acoustic waves (SAWs) [3][4][5][6][7][8][9]. The interaction between SAWs and magnetization dynamics has long been studied [9][10][11][12][13][14][15][16][17][18][19] and there are clear experiments showing the variation of magnetic states caused by SAWs.…”

Parametric Excitation and Instabilities of Spin Waves driven by Surface Acoustic Waves

“…A crucial feature for neural networks is the presence of non-linear processes that start at a certain threshold. Nonlinear higher harmonic spinwave generation induced by SAW has been shown in magnetic semiconductors [33]. However, parametric interaction between spin waves and SAW as predicted by theory [34,35] has not been experimentally demonstrated.…”