Spin-wave bandgap engineering via mode hybridization in dipolar-coupled YIG film/CoFeB nanodisk magnonic crystals

TL;DR

This study demonstrates how hybridization between fundamental and standing spin-wave modes in dipolar-coupled YIG/CoFeB nanodisk magnonic crystals creates tunable bandgaps, enabling reconfigurable magnonic devices.

Contribution

It reveals a novel mechanism for spin-wave bandgap engineering through mode hybridization, beyond traditional Bragg scattering, controlled by geometric and magnetic parameters.

Findings

Pronounced, tunable bandgaps formed via mode hybridization.

Bandgap position and width controlled by nanodisk geometry and magnetic state.

Additional gaps emerge from hybridization with quantized modes at larger lattice periods.

Abstract

We investigate spin-wave transport in hybrid two-dimensional magnonic crystals comprising a low-damping yttrium iron garnet (YIG) film coupled to a periodic array of CoFeB nanodisks. Using propagating spin-wave spectroscopy, super-Nyquist magneto-optical Kerr effect microscopy, and micromagnetic simulations, we demonstrate the formation of pronounced and tunable bandgaps that do not originate from conventional Bragg scattering. Instead, these gaps arise from hybridization between the fundamental magnonic-crystal mode and in-plane transverse standing modes induced by the periodic nanodisk array. The spectral position and width of these gaps are controlled by geometric parameters and by the magnetic state of the nanodisks, including their vortex configuration, which governs both static and dynamic dipolar coupling. For larger lattice periods, additional gaps emerge through hybridization with modes quantized both transverse and parallel to the spin-wave propagation direction, reflecting dispersion folding in two dimensions. Our results establish mode hybridization as a versatile mechanism for engineering spin-wave band structures beyond the constraints of Bragg scattering and provide a pathway toward reconfigurable magnonic devices based on dipolar-coupled hybrid architectures.