Enhancement of the spin-wave nonreciprocity in antiferromagnetically coupled multilayers with dipolar and interfacial Dzyaloshinskii-Moriya interactions

Abstract

Spin-wave-based circuits and logic devices have been considered as an alternative to current electronic devices as they approach the physical limit of miniaturization. Asymmetrical propagation of spin waves, also known as nonreciprocity, provides an additional degree of freedom to these spin-wave-based devices, increasing their flexibility. In thin films, nonreciprocity can be induced by the Dzyaloshinskii-Moriya interaction (DMI) at heavy-metal/ferromagnet bilayers, and by the dipolar coupling in multilayers. Here, we show that in an antiferromagnetically coupled multilayer with interfacial DMI, the frequency nonreciprocity induced by the DMI is enhanced when both heavy metals are the same as long as the multilayer remains in an antiparallel state. Furthermore, we show that the interplay between the dipolar and Dzyaloshinskii-Moriya interaction enhances the nonreciprocity of one oscillation mode and reduces the nonreciprocity of the other. Which mode is enhanced depends on the sign of the induced Dzyaloshinskii-Moriya interaction at the interfaces and the magnetic moments of the layers. Finally, we show that it is possible to change the frequency nonreciprocity of Pt/Co/Cu/Co/Pt and Pt/Co/Cu/Py/Pt multilayers by $\ensuremath{\sim}7$ GHz when applying an in-plane magnetic field of 130 mT. This includes a change in the sign of the nonreciprocity, which could be used to control the direction of the flux of information in spin-wave devices.