Optimizing magneto-optical activity and optical losses in metal-dielectric magnetoplasmonic nanodisks

In this work we show that the insertion of a dielectric layer in Au/Co/Au magnetoplasmonic nanodisks fabricated by hole mask colloidal lithography makes it possible to obtain systems that simultaneously exhibit large magneto-optical (MO) activity and low optical extinction. The physical mechanism underlying this effect is the internal EM field redistribution, in such a way to concentrate it in the MO active layer (Co) and, at the same time, reduce it in the non MO active elements. We have performed a systematic study of the optical and MO response upon the variation of the Co layer thickness within the nanodisk, finding an increase of the MO response with the increment of thickness, accompanied with a blue shift and broadening of the peaks associated with the plasmon excitations.