Imaging Nonlinear Coupling in Focused Magnetoacoustics*

Recently, magneto-acoustic devices have made an impact in applications of RF filtering, communications, and sensing. These devices, which utilize surface acoustic waves (SAWs) coupled to magnetostrictive thin films leverage acoustically driven spin wave resonance (ADSWR) to manipulate microwave signals at low powers and small length scales. However, understandings of physical limitations to engineering improved couplings and careful study of the SAW and magnetization dynamics remain limited.

In this work, we utilize multiple imaging techniques to better understand the acoustic and magnetic behavior of these systems. We employ thin films of Ni or FeGaB grown on YZ-cut LiNbO₃ substrates and pattern curved interdigitated transducers (IDTs) to generate and focus SAWs. Using laser interferometry and Brillouin light scattering (BLS) we investigate the amplitude and spatial behavior of focused SAWs while magneto-optic Kerr effect (MOKE) microscopy enables visualization of SAW induced magnetic domains. By combining these techniques, along with microwave transmission measurements, we reveal a non-linear coupling regime and complex effect on magnetic domain structure. This highlights the role these techniques can play in development of future magnetically coupled materials and devices.