Magneto-plasmonics on perpendicular magnetic nanostructures consisting of a CoPt layer and noble-metal grains

Abstract

The magneto-optical (MO) properties of perpendicular magnetic nanostructures consisting of a hexagonal close-packed Co80Pt20 nanolayer and noble-metal (Ag or Au) fine grains were investigated under polar Kerr measurement conditions. The samples exhibited an unusual MO hysteresis loop in which the Kerr rotation angle increased at a low magnetic field; this effect was observed in a different wavelength region for the CoPt–Ag and CoPt–Au samples. The nanostructures consisted of two magnetic regions of CoPt layers formed on the grains and on the underlayer. The increase in the Kerr angle was induced by the antiparallel magnetic alignment of these CoPt layers. The opposite MO polarity on the CoPt nanostructures was suggested in a micro-MO observation using scanning near-field polarized optical microscopy. The Ag and Au fine grains induced the MO phase reversal of CoPt in a different wavelength region for each sample. These MO behaviors were attributed to the influence of localized surface plasmons excited on the noble-metal grains. The magneto-plasmonic activities on the CoPt nanostructures were also affected by the underlayer material and the environmental conditions. The perpendicular magnetic nanostructures are expected to provide a new type of probe for chemical and biological sensing applications.