Broken intrinsic symmetry induced magnon-magnon coupling in synthetic ferrimagnets

TL;DR

This paper reports on the discovery of a broken intrinsic symmetry that enables coupling between acoustic and optical magnons in synthetic ferrimagnets, with a large, controllable hybridization gap.

Contribution

It demonstrates a new mechanism for magnon-magnon coupling induced by broken symmetry in synthetic ferrimagnets, with tunable hybridization strength.

Findings

Hybridization occurs at degeneracy points with avoided level-crossing.

The gap size can be controlled by interlayer exchange interaction.

A maximum gap of 3.9 GHz exceeds typical magnonic hybrid systems.

Abstract

Synthetic antiferromagnets offer rich magnon energy spectra in which optical and acoustic magnon branches can hybridize. Here, we demonstrate a broken intrinsic symmetry induced coupling of acoustic and optical magnons in a synthetic ferrimagnet consisting of two dissimilar antiferromagnetically interacting ferromagnetic metals. Two distinct magnon modes hybridize at degeneracy points, as indicated by an avoided level-crossing. The avoided level-crossing gap depends on the interlayer exchange interaction between the magnetic layers, which can be controlled by adjusting the non-magnetic interlayer thickness. A large avoided level crossing gap of 3.9 GHz is revealed, exceeding the coupling strength that is typically found in other magnonic hybrid systems based on a coupling of magnons with photons or magnons with phonons.