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(t__\scriptstyle \rm Ir=0.6 nm, 1.2 nm)/CoFeB(13 nm). Remarkably, we find that the weakly uniaxial anisotropy field (\sim 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 t__\scriptstyle \rm Ir =0.6 nm, and between 0.09 GHz and 1.4 GHz for t__\scriptstyle \rm Ir = 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.