Magnetoplasmonics in split ring-ring structures fabricated with hole-mask colloidal lithography

Large enhancements of the magneto-optical (MO) activity by the localized surface plasmon resonance (LSPR) have been reported in structures like nanodisks, core-shell nanoparticles, dimers, etc.. In this contribution, we extend this application to the magnetoplasmonic split ring-ring structure. With the hole-mask colloidal lithography method (Fig. 1(a)), a split Au ring is generated on the bottom Au ring with a Co-dot embedded inside (Fig. 1(b)). By properly optimizing the gap angle of the split ring, the electromagnetic field is redistributed and focused in the MO active Co area, therefore the MO activity obtains a boost and is maximized for the structure with a gap of 60 deg angle, by an enhancement factor of 3 compared to the one without gap (Fig. 1(c)). The EM field redistribution and focus around the gap area is confirmed via EELS-TEM mapping (inset Fig. 1(c)).