Symmetry breaking induced magnon-magnon coupling in synthetic antiferromagnets

We propose a general theory of microwave absorption spectroscopy for symmetry-breaking synthetic antiferromagnets (SAFs). Generally, inhomogeneity or different thickness the two ferromagnetic sublayers SAF results in intrinsic symmetry breaking, while out-of-plane components dc magnetic fields lead to extrinsic one. The broken SAFs excludes original symmetry-protected crossing between pure in-phase and out-of-phase resonance modes with opposite parity. Alternatively, new frequency branches become hybridization bare terms symmetry-breaking-induced magnon-magnon coupling, which an indirect gap frequencies. Also, dependence width on degree breaking several typical cases are presented compared existing experiments. Our provides simple but physical understanding rich structure spectra asymmetric SAFs.