Strong plasmon enhancement of magneto-optical Kerr rotation in Co–AlO nanogranular films coated with gold nanoparticles

We report on the enhancement of magneto-optical Kerr rotation in Co-AlO nanogranular films coated with gold nanoparticles (NPs) of different shapes. For these nanostructures, the Kerr rotation spectra measured from 1.0 to 5 eV show a peak at about 2.1 eV which is about one order of magnitude higher than that obtained for pure Co-AlO films under similar conditions. We demonstrate that the Kerr rotation intensity increases as the Au NPs' shape changes from nanospheres to nanoprisms. The highest enhancement observed for the nanoprisms is due to the presence of a maximum number of sharp edges or surface active rough areas compared to the smooth surfaces of the nanospheres. The Kerr rotation enhancement corresponds to intrinsic electronic transitions in the Co nanogranules due to plasmonic interactions between closely spaced Au and Co nanostructures. This high enhancement factor of these multiple-shaped Au NPs might find potential application in the detection of single molecules, in bio-diagnosis, and in medical therapy.