Anisotropic Magnon–Magnon Coupling in Synthetic Antiferromagnets

Magnon-magnon coupling in synthetic antiferromagnets advances it as hybrid magnonic systems to explore the quantum information technologies.To induce magnon-magnon coupling,the parity symmetry between two magnetization needs to be broken.Here we experimentally demonstrate a convenient method to break the parity symmetry by the asymmetric structure.We successfully introduce a magnon-magnon coupling in Ir-based synthetic antiferromagnets CoFeB(10 nm)/Ir(tIr=0.6 nm,1.2 nm)/CoFeB(13 nm).Remarkably,we find that the weakly uniaxial anisotropy field(～20 Oe) makes the magnon-magnon coupling anisotropic.The coupling strength presented by a characteristic anticrossing gap varies in the range between 0.54 GHz and 0.90 GHz for tIr=0.6 nm,and between 0.09 GHz and 1.4 GHz for tIr=1.2 nm.Our results demonstrate a feasible way to induce magnon-magnon coupling by an asymmetric structure and tune the coupling strength by varying the direction of in-plane magnetic field.The magnon-magnon coupling in this highly tunable material system could open exciting perspectives for exploring quantum-mechanical coupling phenomena.