Large Nonreciprocal Propagation of Surface Acoustic Waves in Epitaxial Ferromagnetic/Semiconductor Hybrid Structures

Abstract

Nonreciprocal propagation of sound, that is, the different transmission of acoustic waves traveling in opposite directions, is a challenging requirement for the realization of devices such as acoustic isolators and circulators. Here, we demonstrate efficient nonreciprocal transmission of surface acoustic waves (SAWs) propagating in opposite directions in a GaAs substrate coated with an epitaxial Fe3Si film. The nonreciprocity arises from the acoustic attenuation induced by the magnetoelastic (ME) interaction between the SAW strain field and spin waves in the ferromagnetic film, which depends on the SAW propagation direction and can be controlled via the amplitude and orientation of an external magnetic field. The acoustic-transmission nonreciprocity, defined as the difference between the transmitted acoustic powers for forward and backward propagation at the ME resonance, reaches values of up to 20%, which are, to our knowledge, the largest values of nonreciprocity reported for SAWs traveling in a semiconducting piezoelectric substrate covered by a ferromagnetic film. The experimental results are well accounted for by a model for the ME interaction, which also shows that the nonreciprocity can be further enhanced by optimization of the sample design. These results make Fe3Si/GaAs a promising platform for the realization of efficient nonreciprocal SAW devices.