Plasmon modes characterization in hybrid noble/ ferromagnetic nanodisks using an effective medium approximation

Magneto-plasmonic systems composed by noble/ferromagnetic metals structures can be used to control light polarization. The extraordinary optical properties arising from combining strong local enhancements of electromagnetic fields in surface plasmon excitations with the magneto-optical activity inherent to ferromagnetic materials, can be controlled by external magnetic fields that have demonstrated the possibility to control and amplify the magneto-optical properties via plasmonic excitations. In this work, the anisotropic optical and ellipsometric sensitivity to dielectric environment of multi-layered hybrid gold/cobalt magnetoplasmonic nanodisks are studied in the framework of the effective-medium approximation, where the components of the dielectric tensor of the system are modelled using Lorentz-like oscillators. Furthermore, full electromagnetic simulations were performed using the standard Finite Element Method, which allow us to characterize the modes and explore the role of the dielectric environment of the nanodisks in the optical properties of the nanostructures via the variation of a coating silicon dioxide (SiO2) layer thickness. Our model and numerical results show a very good agreement with spectral ellipsometry measurements, where two orthogonal plasmonic modes one in-plane and one out-of-plane- are well characterized. These results lead us to conclude that the effective-medium approximation is good enough to accurately describe the plasmonic behavior of multi-layered confined nanostructures.