Spin-wave mode reversal and anisotropy in bicomponent magnonic crystals

Bicomponent magnonic crystals (BMCs) are engineered metamaterials comprised of magnetic materials with contrasting properties that offer a wide range of tunability in spin-wave (SW) dynamics, making them highly relevant for modern magnonic and spintronic devices. Herein, the magnetic configuration driven SW dynamics of BMC, having Permalloy (Ni₈₀Fe₂₀) inclusion of circular and square shapes in Co₅₀Fe₅₀ matrix, have been extensively studied using ferromagnetic resonance spectroscopy and micromagnetic simulation. The experimentally obtained magnetic field dispersion confirms the theoretically predicted SW mode reversal. In this phenomenon, the SW mode with the highest frequency, typically excited in the region of high saturation magnetization under a higher applied bias field, undergoes a transition, becoming the mode with the lowest frequency as the applied field decreases. Furthermore, we observed mode splitting and mode merging alongside the conventional monotonic variation of SW modes with changes in the applied bias field. The numerically simulated mode profile shows the bias field dependent preferential spatial excitation of SW modes, originating from the spatial distribution of the demagnetizing field. The magnetic microstate dependent spatial distribution of the demagnetizing field leads to the creation, distortion, and annihilation of positively and negatively demagnetized channels, which act as roadways for SW propagation.