Spin waves form the basis for the field of magnonics, where they are used for information transport and processing [1]. Acoustic waves, in particular surface acoustic waves (SAWs), are widely employed as frequency filters in mobile communication technology. SAWs have group velocities comparable to that of spin waves and consequently can be generated with magnon-compatible wavelengths and at microwave frequencies. In magnetic media, spin waves can interact with SAWs which defines the field of magnetoacoustics. Magneto-acoustic devices can be used to excite and detect magnetization dynamics acoustically and control SAW propagation magnetically. Because of the ellipticity of the magneto-acoustic driving fields, as well as the spin-wave non-reciprocity due to dipolar coupling and the Dzyaloshinskii-Moriya interactions [2,3], magneto-acoustic waves are thereby generally chiral and non-reciprocal [4].

I will discuss the symmetry and non-reciprocity of magneto-acoustic waves in magnetically ordered thin films and heterostructures [5-7]. We quantitatively model the SAW-spin wave interaction based on the Kalinikos-Slavin equation and spin wave excitation by elliptically polarized coherent phonons to reveal that the magnon-phonon coupling is driven not only by magneto-elastic interactions [8] but also by magneto-rotation [5,9]. The efficient coupling of SAWs and spin waves can also be used to explore non-linear magneto-acoustic dynamics [10]. Non-linear and non-reciprocal magneto-acoustic waves may be useful for the implementation of miniaturized on-chip microwave components.

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[4] M. Küß et al., Frontiers in Physics 10, (2022).
[5] M. Küß et al., Phys. Rev. Lett., 125, 217203 (2020).
[6] M. Küß et al., Phys. Rev. Applied, 15, 034060 (2021).
[7] M. Küß et al., Phys. Rev. Applied, 15, 034046 (2021).
[8] M. Weiler et al., Phys. Rev. Lett. 106, 117601 (2011).
[9] M. Xu et al., Sci. Adv. 6, eabb1724 (2020).
[10] M. Geilen et al., arXiv:2201.04033 (2022).