Anisotropic magnon-magnon coupling mediated by exchange bias in CoZr/Ru/FeNi/IrMn films

Coupled-magnon systems provide unique avenues for information exchange and energy transport in spintronic devices. The parity symmetry of these systems plays a crucial role in the introduction of magnon-magnon coupling. In this study, we break the parity symmetry by stacking different ferromagnetic layers in synthetic antiferromagnets CoZr/Ru/FeNi. This results in the hybridization between acoustic-type and optical-type magnons, forming an anticrossing gap. This gap signifies the presence of anisotropic magnon-magnon coupling driven by uniaxial magnetic anisotropy. Additional sputtering of IrMn on the FeNi sublayer results in robust unidirectional magnon hybridization. Both experimental and theoretical analyses indicate that the breaking of parity symmetry and coupling strength are well described by the angle between the total magnetization and the applied in-plane magnetic field qualitatively. The exchange bias in FeNi induced by IrMn can further enhance or suppress this symmetry breaking, transitioning the anisotropic coupling from twofold to unidirectional. This readily adjustable magnon hybridization presents promising opportunities for advancing unidirectional energy and information transfer in magnonic technologies.