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Optical detection of magneto-acoustic dynamics

Abstract : In the developing field of spin wave-based information technology, this work investigates the possibility to use surface acoustic waves (SAW) to excite spin-wavesin ferromagnetic thin layers relying on the magnetoelastic coupling. This would provide a non-inductive, efficient, and remote addressing of spin waves. In the first project we develop an experimental setup to generate electrically excited SAWs phase-locked to probe laser pulses. The magnetization dynamics is detected by an optical bridge using magneto-optical effects (Kerr and Voigt). We investigate the resonant magneto-elastic coupling in a thin film of the ferromagnetic semiconductor (Ga,Mn)As. To reach resonant coupling, the spin-wave frequency is scanned across the SAW frequency using a magnetic field. We disentangle the photoelastic contribution from the magneto-optical one, from which we obtain the amplitude of magnetization precession. We show that it is driven solely by the acoustic wave. Its field dependence is shown to agree well with theoretical calculations. Its amplitude resonates at the same field as the resonant attenuation of the acoustic wave, clearly evidencing the magnetoacoustic resonance with high sensitivity. The influence of temperature, SAW frequency and power on the coupling efficiency are studied. In the second project we use SAWs thermoelastically excited by a tightly focused laser beam on ferromagnetic metals (Ni, FeGa, Co) on a transparent substrate (glass, sapphire). Spatio-temporal maps of the surface displacement and magneto-optical signal are obtained. A high-frequency shift of the frequency spectrum of the latter gives a hint for spin-wave excitation by SAWs.
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Contributor : Piotr Kuszewski <>
Submitted on : Thursday, December 13, 2018 - 12:05:37 PM
Last modification on : Friday, May 29, 2020 - 3:57:26 PM
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  • HAL Id : tel-01953825, version 1


Piotr Kuszewski. Optical detection of magneto-acoustic dynamics. Physics [physics]. Sorbonne Université; Institut des NanoSciences de Paris, 2018. English. ⟨tel-01953825⟩



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