Temperature dependence of the magnon-phonon interaction in hybrids of high-overtone bulk acoustic resonators with ferromagnetic thin films
Manuel Müller, Johannes Weber, Sebastian T. B. Goennenwein, Silvia Viola Kusminskiy, R. Gross, Matthias Althammer, Hans Huebl
Abstract
Tailored magnon-phonon hybrid systems, in which high-overtone bulk acoustic resonators couple resonantly to the Kittel mode of a ferromagnetic thin film, are considered optimal for the creation of acoustic phonons with a defined circular polarization. This class of devices is therefore ideal for the investigation of phonon-propagation properties and assessing their capacity to transport angular momentum in the classical, and potentially even in the quantum, regime. Here, we study the coupling between the magnons in a ferromagnetic $\mathrm{Co}$${}_{25}$$\mathrm{Fe}$${}_{75}$ thin film and the transverse acoustic phonons in bulk acoustic wave resonators formed by the sapphire substrate onto which the film is deposited. Using broadband ferromagnetic resonance experiments as a function of temperature, we investigate the strength of the coherent magnon-phonon interaction and the individual damping rates of the magnons and phonons participating in the process. This demonstrates that this coupled magnon-phonon system can reach a cooperativity $C\ensuremath{\approx}1$ at cryogenic temperatures. Our experiments also showcase the potential of strongly coupled magnon-phonon systems for strain-sensing applications.