Non-reciprocal microwave components such as circulators, isolators, and phase shifters are indispensable tools in both today’s communication systems and future quantum computers 1-2. However, these components rely almost entirely on field-based bulky ferrimagnet, which tend to be relatively large, off-chip, and costly to assemble. In this context, different fields of research are investigating solutions to miniaturize these non-reciprocal devices compatible with integrated circuit technology. Among them, the field of magnonic plays a key role in this search benefiting from a wide range of non-reciprocal properties in the propagation of spin waves 3. Recently, unidirectional transmission of spin waves was achieved by taking advantage of the chiral coupling between the uniform resonance of Co nanowires and exchange spin waves in a thin YIG film 4, 5. Here, we further miniaturized this method and demonstrate the possibility of shaping non-reciprocal spin wave beams in a continuous thin YIG film. We performed spin wave spectroscopy on a series of devices made of arrays of Co bars of dimensions: L=10µm in length, w=200 nm in width, 40nm in thickness, and laterally spaced by a=400nm (see Fig. 1). The transmission spectra done with the external field applied along the length of the Co bars show perfect non-reciprocity for several peaks located around the resonance frequency of the Co bars, e.g. 8.4 to 10.4 GHz range as shown in Fig. 2. These peaks correspond to integer values of the lateral spacing between Co bars, e.g. kn=nπ/a ranging up to 80rad/µm. Additional non-reciprocal peaks occurring at lower frequencies ranging between 2 and 6 GHz correspond to the satellite peaks of the antenna directly coupled to the YIG film. Surprisingly, some of the peaks display a reversed non-reciprocity. Finally, we make use of this multitude of transmission peaks to characterize the k-dependence of the relaxation time and the group velocity of dipole-exchange spin waves.
References 87.png)1 W. Palmer, et al., IEEE Micr. Magazine 20, 36 (2019)
2 M. Devoret, et al., Superconducting circuits for quantum information,Science 339, 1169 (2013)
3 J. Chen, et al., J. Phys. D. Appl. Phys. 55, 123001 (2022)
4 H. Wang, et al., Nano Res. 14, 2133–2138 (2021)
5 J. Chen, et al., Phys. Rev. B 100, 104427 (2019)

SEM image of Co nanowires with length L=10μm, width w=200nm, and period a=400nm lithographed on a 50nm YIG film with thickness, and located under 2 µm wavelength Au coplanar waveguides (CPW)

Transmission spectrum ΔL₂₁ (blue) and ΔL₁₂ (red) at 24mT applied field.