Strong Magnon-Magnon Coupling in Synthetic Antiferromagnets

TL;DR

This paper demonstrates theoretically and numerically that strong and tunable magnon-magnon coupling, including ultrastrong coupling, can be achieved in synthetic antiferromagnets by symmetry breaking and parameter tuning.

Contribution

It introduces the concept of strong and ultrastrong magnon-magnon coupling in synthetic antiferromagnets and shows how to control it via system parameters.

Findings

Strong coupling between acoustic and optic magnon modes demonstrated.

Coupling strength can be highly tuned by system parameters.

Ultrastrong coupling regime achievable.

Abstract

Synthetic antiferromagnet, comprised of two ferromagnetic layers separated by a non-magnetic layer, possesses two uniform precession resonance modes: in-phase acoustic mode and out-of-phase optic mode. In this work, we theoretically and numerically demonstrated the strong coupling between acoustic and optic magnon modes. The strong coupling is attributed to the symmetry breaking of the system, which can be realized by tilting the bias field or constructing an asymmetrical synthetic antiferromagnet. It is found that the coupling strength can be highly adjusted by tuning the tilting angle of bias field, the magnitude of antiferromagnetic interlayer exchange coupling, and the thicknesses of ferromagnetic layers. Furthermore, the coupling between acoustic and optic magnon modes can even reach the ultrastrong coupling regime. Our findings show high promise for investigating quantum phenomenon with a magnonic platform.