Enhanced Faraday Effect in Porous Iron Oxide Thin Films Coupled to Localized Surface Plasmon Resonances

Abstract

We have examined the Faraday effect for iron oxide thin films deposited with silver nanoparticles. The iron oxide thin films were fabricated by using an epoxide-catalyzed sol-gel method assisted by water-soluble polymers. A single spin-coating process followed by a sequence of heat treatments allows the fabrication of polycrystalline γ–Fe₂O₃ thin layers with a porous morphology and a transparent appearance. The sample deposited with silver nanoparticles shows optical extinction ascribed to the localized surface plasmon resonances (LSPRs) ranging from 460 − 674 nm, depending on the size of nanoparticles. The magnitude of the Faraday rotation angle is enlarged around the wavelengths of LSPRs, showing a slight redshift of the wavelength of maximum enhancement with respect to the spectral position of the LSPRs. The numerical simulation explains that the shift is caused by the difference between far-field extinction and near-field enhancement of the electric field at the surface of the nanoparticle.