Faraday rotation enhancement due to proximity effect of surface plasmon resonance in magnetoplasmonic colloidal mixtures

The modification of Magneto-optic Faraday Rotation (MFR) based on Surface Plasmon Resonance (SPR) of noble metal nanoparticles (NP) has been an exciting field of research. The underlying physical mechanisms are intriguing and correspond to various observation patterns in composite magnetoplasmonic systems. Exploiting the immense potential of SPR phenomenon for excellent electromagnetic field confinement and energy transfer to a wide variety of dimensionally different nanostructures, we report MFR measurements in typical magnetoplasmonic colloidal mixtures of separately synthesized cobalt ferrite (CoFe2O4) and gold (Au) NP at wavelength of 532 nm where we have observed a spectacular possibility for "proximity effect" based plasmonic enhancement of MFR, for the very first time. The Langevin-type MFR patterns show a strong dependence on the concentrations of participating systems, where a typical optimum concentration produced a significant enhancement in MFR. For both the entities present in the liquid, a mutually dependent optimum concentration was necessary to obtain the Langevin pattern as well as MFR enhancement, confirming the influence from SPR due to the proximity effect. The observations open up exciting possibilities to apply SPR to discover novel magnetoplasmonic phenomena underlined by proximity effects, in addition to eluding constrained procedures to synthesize composite magnetoplasmonic systems.