This work investigates the spin-wave dynamics in thick one-dimensional bicomponent magnonic crystals, focusing on the interplay between geometric confinement, material contrast, and dipolar exchange interactions. Using a combined plane-wave and dynamic-matrix formalism, the magnonic band structure and mode profiles are calculated for both Damon-Eshbach (DE) and backward-volume (BV) geometries, explicitly accounting for nonuniform dynamic magnetization across the film thickness. As a reference system, a uniform-thickness magnonic crystal is analyzed, revealing that the macrospin approximation fails beyond a critical thickness due to hybridization with higher-order perpendicular standing spin-wave modes, leading to nonmonotonic variations in the bandgap width and position. When vertical material contrast is introduced, pronounced localization phenomena emerge: in the DE configuration, low-frequency modes concentrate within the low-saturation-magnetization material through field-induced frequency detuning; in the BV geometry, the demagnetizing-field landscape generates flat, defect-like modes localized within the high-saturation-magnetization regions. These localization mechanisms remain robust over wide ranges of thickness and filling fraction and display a clear crossover from exchange-dominated uniform profiles in thin films to strongly confined modes in thicker structures. The results provide a comprehensive description of spin-wave behavior in three-dimensional periodic magnetic systems and offer design guidelines for magnonic architectures requiring tailored dispersion and controllable modal confinement.

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• Magnetization dynamics
• Spin dynamics
• Layered crystals
• Landau-Lifshitz model
• Linear spin wave theory
• Plane-wave expansion