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

Abstract

Non-reciprocal propagation of sound, that is, the different transmission of acoustic waves traveling along opposite directions, is a challenging requirement for the realization of devices like acoustic isolators and circulators. Here, we demonstrate the efficient non-reciprocal transmission of surface acoustic waves (SAWs) propagating along opposite directions of a GaAs substrate coated with an epitaxial Fe$_3$Si film. The non-reciprocity arises from the acoustic attenuation induced by the magneto-elastic (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 non-reciprocity, defined as the difference between the transmitted acoustic power for forward and backward propagation under ME resonance, reaches values of up to 20%, which are, to our knowledge, the largest non-reciprocity reported for SAWs traveling along a semiconducting piezoelectric substrate covered by a ferromagnetic film. The experimental results are well accounted for by a model for ME interaction, which also shows that non-reciprocity can be further enhanced by optimization of the sample design. These results make Fe$_3$Si/GaAs a promising platform for the realization of efficient non-reciprocal SAW devices.