Microstructure and magneto-optical surface plasmon resonance of Co/Au multilayers

Magneto-optical surface plasmon resonance (MOSPR) sensors benefit from a magneto-optic enhancement with respect to surface plasmon resonance (SPR) sensors, making these devices attractive for biosensing applications. Typical design compromises seek to balance magneto-optic effects and optical losses associated with surface plasmon waves extending to the ferromagnetic layer. Here, we demonstrate that Co/Au multilayers can yield sizeable MOSPR improvements in spite of the relative high total Co layer thickness. Co(t(Co))/Au(2 nm) multilayers, with 1.2 <= t(Co) <= 1.8 nm are prepared and characterized. X-ray analysis shows that the microstructure maintains high layer periodicity and improves upon annealing. The multilayer structures were then modeled to study their SPR/MOSPR sensitivities, suggesting that the MOSPR sensitivity is enhanced by a factor of up to 3 and 4 with respect to the SPR sensitivity when the devices are operated in Air and Water media, respectively. We find that multilayers provide a particular advantage when operating the sensors in Water-based media.