  The use of a complex ferromagnetic system to manipulate GHz surface acoustic
waves is a rich current topic under investigation, but the high-power nonlinear
regime is under-explored. We introduce focused surface acoustic waves, which
provide a way to access this regime with modest equipment. Symmetry of the
magneto-acoustic interaction can be tuned by interdigitated transducer design
which can introduce additional strain components. Here, we compare the impact
of focused acoustic waves versus standard unidirectional acoustic waves in
significantly enhancing the magnon-phonon coupling behavior. Analytical
simulation results based on modified Landau-Lifshitz-Gilbert theory show good
agreement with experimental findings. We also report nonlinear input power
dependence of the transmission through the device. This experimental
observation is supported by the micromagnetic simulation using mumax3 to model
the nonlinear dependence. These results pave the way for extending the
understanding and design of acoustic wave devices for exploration of
acoustically driven spin wave resonance physics.
