Nonreciprocity of Phase Accumulation and Propagation Losses of Surface Acoustic Waves in Hybrid Magnetoelastic Heterostructures

Lack of nonreciprocity-in particular, nonreciprocity of phase accumulation-is one of the major drawbacks of microwave solid-state acoustic devices, which has prevented the development of acous-tic isolators and circulators. Here we report the observation of the phase nonreciprocity of hybridized surface acoustic waves (SAWs) and spin waves in a magnetoelastic heterostructure. Our system consists of a Fe-Ga-B/Al2O3/Fe-Ga-B multilayer on top of a LiNbO3 crystal. Maximum values of the observed nonreciprocal phase accumulation easily exceed pi radians over a broad range of field conditions, which is necessary for the development of an effective circulator. In addition, under the application of bias magnetic field, the structure demonstrates tunable giant nonreciprocity of propagation losses with isolation as high as 48 dB, necessary for the development of isolators. Theoretical calculations provide an insight into the observed phenomena and demonstrate a pathway for further improvement of nonreciprocal SAW devices based on magnetoelastic coupling.