Observation of mode splitting by magnon–magnon coupling in synthetic antiferromagnets

Abstract We investigated the coherently excited propagating magnons in in-plane magnetized synthetic antiferromagnets using heterodyne-magneto-optical Kerr effect technique. Under the in-plane magnetic field to 45° away from the magnon propagation direction, we observed the mode splitting of magnon dispersion relation due to the magnon–magnon coupling between acoustic and optical magnon modes. The strong coupling with a cooperativity of 8.4 ± 1.3 is achieved for finite wavenumber. These results provide a deep understanding of the properties of coherently excited magnons in synthetic antiferromagnets, which will be helpful for designing advanced magnonic devices.