Strong magnon-magnon coupling in an ultralow damping all-magnetic-insulator heterostructure

TL;DR

This paper demonstrates strong, tunable magnon-magnon coupling in an all-insulating TmIG/YIG heterostructure with ultralow damping, enabling advanced magnonic device applications.

Contribution

It reports the first realization of strong, coherent magnon-magnon coupling in an all-insulator heterostructure with ultralow damping, surpassing metal-based systems.

Findings

Achieved high cooperativity in TmIG/YIG heterostructure

Coupling strength tunable via layer thickness and magnon modes

Validated results with analytical and micromagnetic models

Abstract

Magnetic insulators such as yttrium iron garnets (YIGs) are of paramount importance for spin-wave or magnonic devices as their ultralow damping enables ultralow power dissipation that is free of Joule heating, exotic magnon quantum state, and coherent coupling to other wave excitations. Magnetic insulator heterostructures bestow superior structural and magnetic properties and house immense design space thanks to the strong and engineerable exchange interaction between individual layers. To fully unleash their potential, realizing low damping and strong exchange coupling simultaneously is critical, which often requires high quality interface. Here, we show that such a demand is realized in an all-insulator thulium iron garnet (TmIG)/YIG bilayer system. The ultralow dissipation rates in both YIG and TmIG, along with their significant spin-spin interaction at the interface, enable strong and coherent magnon-magnon coupling with a benchmarking cooperativity value larger than the conventional ferromagnetic metal-based heterostructures. The coupling strength can be tuned by varying the magnetic insulator layer thickness and magnon modes, which is consistent with analytical calculations and micromagnetic simulations. Our results demonstrate TmIG/YIG as a novel platform for investigating hybrid magnonic phenomena and open opportunities in magnon devices comprising all-insulator heterostructures.