  The interaction between surface acoustic waves (SAWs) and spin waves (SWs) in
a piezoelectric/magnetic thin film heterostructure yields potential for the
realization of novel microwave devices and applications in magnonics. In the
present work, we investigate the SAW-SW interaction in a Pt/Co(2 nm)/Ru(0.85
nm)/Co(4 nm)/Pt synthetic antiferromagnet (SAF) composed of two ferromagnetic
layers with different thicknesses separated by a thin nonmagnetic Ru spacer
layer. Because of the combined presence of interfacial Dzyaloshinskii--Moriya
interaction (iDMI) and interlayer dipolar coupling fields, the optical SW mode
shows a large nondegenerate dispersion relation for oppositely propagating SWs.
Due to SAW-SW interaction, we observe nonreciprocal SAW transmission in the
piezoelectric/SAF hybrid device. The equilibrium magnetization directions of
both Co layers are manipulated by an external magnetic field to set a
ferromagnetic, canted, or antiferromagnetic configuration. This has a strong
impact on the SW dispersion, its nonreciprocity, and SAW-SW interaction. The
experimental results are in agreement with a phenomenological SAW-SW
interaction model, which considers the interlayer exchange coupling, iDMI, and
interlayer dipolar coupling fields of the SWs.
