Dominant role of iron oxides in magnetic circular dichroism of plasmonic-magnetic Au-Fe3-xO4 heterodimer nanostructures

Plasmon-tuned magneto-optical (MO) properties enable design concepts of MO devices with various nanoarchitectures. In this study, magnetic circular dichroism (MCD) is presented in plasmonic-magnetic Au-Fe3-xO4 heterodimer nanostructures dispersed in solution. The heterodimers are synthesized by thermal decomposition of Fe(III) precursors in the presence of preformed Au nanoparticles. The extinction spectrum exhibits a localized surface plasmon resonance (LSPR) peak, which is red-shifted with respect to the isolated Au particle resonance. On the other hand, the MCD response is overwhelmingly dominated by iron oxide counterparts consisting of multiphase magnetite (Fe3O4)/maghemite (gamma-Fe2O3). No appreciable LSPR-enhancement in the MO response is found. As for the effect of the magnetic component on the LSPR behavior of Au, a decrease in the magnetoplasmonic response is observed. This suggests a reduction of the effective magnetic field to the Au counterparts, which can probably be due to magnetic shielding by the iron oxides in the near vicinity of Au nanoparticles.