Synergistic enhancement of magneto-optical response in cobalt-based metasurfaces via plasmonic, lattice, and cavity modes

Static metasurfaces offer precise control over light but lack reconfigurability, limiting their use in dynamic applications. Introducing tunability via external stimuli, such as magnetic fields, enables active control of their optical response, broadening their functionality. In this computational study, we present the design of a metal-dielectric-metal magnetoplasmonic metasurface with improved magnetic field tunability, surpassing the magneto-optical response of unstructured ferromagnetic materials. This improvement arises from the synergistic effect of localized plasmon excitation, surface lattice resonance, and Fabry-Pérot cavity modes. The design approach presented here consists in matching the characteristic resonance frequencies of the three phenomena by iteratively adjusting the structural parameters of the metasurface: nanostructure size, lattice period, and cavity layer thickness. This optimization led to a substantial enhancement in the reflectance modulation induced by an external magnetic field, with the overall contrast exceeding that of an unstructured cavity by more than an order of magnitude across various regions of the visible to near-infrared spectrum, under relatively low magnetic fields. This unique capability makes the system a promising tool for magnetic field-sensitive optical modulation of reflected light intensity, with potential applications as a laser amplitude modulator.