Wide-Band Nonreciprocal Transmission of Surface Acoustic Waves in Synthetic Antiferromagnets

The coupling between surface acoustic waves (SAWs) and spin waves (SWs) in piezoelectric/magnetic heterostructures holds potential for the realization of novel microwave devices. Since SAWs are inherently reciprocal, the nonreciprocity arising from magnetoacoustic interaction is of particular interest. Large nonreciprocal SAW transmission in a limited frequency range near the intersection point of the SAW and SW dispersions has been recently reported in several studies. Here, we demonstrate that the nonreciprocal SW dispersion of a CoFeB(16 nm)/Ru(0.55 nm)/CoFeB(14 nm) synthetic antiferromagnet (SAF) can be adjusted to match the linear dispersion of the SAW in a wide range of frequencies f. Therefore, the SAW transmission is nonreciprocal for 2.8 GHz < f < 7.0 GHz with low losses (<0.08 dB) mediated by SAW-SW interaction in the forward direction and large attenuation (>5 dB) in the reverse direction. These results hold great potential for the realization of devices allowing wide-band nonreciprocal signal transmission.