Broadband zero-field nonreciprocity of surface acoustic waves coupled to magnons in synthetic antiferromagnets.

Broadband nonreciprocal propagation of surface acoustic waves (SAWs) can be realized by magnetoelastic coupling between SAWs and nonreciprocal spin waves in a synthetic antiferromagnet (SAF). Developing strategies to achieve strong SAW nonreciprocity at zero magnetic field is essential for implementation for nonreciprocal microwave devices. We will present measurements demonstrating robust zero-field broadband SAW nonreciprocity engineered through control of the angle between the SAF's uniaxial magnetic anisotropy axis and the SAW propagation direction. Time-domain measurements of nanosecond SAW wave-packet propagation reveal zero-field broadband nonreciprocity up to 17 dB at 3 GHz. These findings establish design principles for compact, integrated, and field-free nonreciprocal microwave components such as isolators and circulators.