Magnon up-conversion mediated by nonlinear harmonic generation in synthetic antiferromagnets

The conversion of magnons between distinct modes enables advanced nonlinear manipulation of these quasiparticles. Synthetic antiferromagnets (SAFs) with their inherently coupled magnon modes provide a promising platform for such conversion. However, the underlying physical mechanism governing magnon conversion remains to be elucidated. With the micromagnetic simulation, we investigate the nonlinear process of magnon upconversion mediated by second harmonic generation (SHG) in SAFs. We find that the SHG of acoustic mode magnons can act as a driven-field to pump optical mode magnons, enabling efficient energy transfer between them. When the resonance frequency of the acoustic mode is half that of the optical mode magnons, this nonlinear process maximizes the conversion efficiency. Furthermore, coherent control of optical mode population is achieved by synchronizing the phase of SHG-pumping and direct microwave excitation. It provides a mechanism for programmable spin-wave signal processing based on nonlinear magnon conversion, which is the building block for magnonic computing beyond von Neumann architectures.