Bilayer magnonic crystal directional coupler: Interlayer spin-wave coupling and formation of localized beams within a three-dimensional magnonic architecture

We provide results of frequency-selective spin-wave channeling in a bilayer magnonic crystal structure. We report the results of an experimental and numerical study of the propagation of spin waves in a multilayer in-plane-magnetized magnonic crystal structure, which consists of two layers of yttrium iron garnet films located one above the other. Each layer has a lateral system of spin-wave waveguide channels separated by an array of grooves in the form of a one-dimensional magnonic crystal on the surface of yttrium iron garnet. The regimes of frequency-selective signal separation inside the evolved channels in either the bottom layer or the upper layer were revealed by the use of Brillouin light scattering and microwave spectroscopy. The simultaneous effect of magnonic band gap formation and dipolar coupling of propagated spin waves reveals itself in the localized spin-wave beam formation and propagation along one of the four channels. This mechanism was investigated by a numerical simulation based on the electrodynamic three-dimensional model and semianalytical eigenmode composition along the micromagnetic simulation. It is demonstrated that the proposed method of spin-wave transport control can find application in the fabrication of demultiplexers and magnonic logic elements based on the principles of spatial-frequency selection of a microwave signal in multilayer topologies of magnonic devices.