Electrically Controlled Nonlinear Magnon-Magnon Coupling in a Synthetic Antiferromagnet.

We investigate the nonlinear coupling between acoustic (ac) and optical (op) modes in the coupled magnetization dynamics of synthetic antiferromagnets, utilizing current-driven resonance spectroscopy. A clear spectral splitting is evident in the ac mode when strongly excited by the radio frequency current at a driving frequency half that of the op mode resonance. The Landau-Lifshitz phenomenology aligns with the experimental observations, affirming the coupling of the radio-frequency-excited ac and op modes through three-magnon mixing. The nonlinearity enables a Rabi-like splitting in an in-plane magnetized synthetic antiferromagnet without breaking its natural symmetries. This discovery holds potential for advancing our understanding of nonlinear antiferromagnetic dynamics.