Magneto-optical efficiencies combined with surface-plasmon resonance in FeSi/Au system

Abstract

We designed and fabricated our original laminated materials that simultaneously exhibited different properties: magneto-optical (MO), i.e., the transverse MO Kerr effects (T-MOKE) and surface-plasmon resonance (SPR). The material design was composed of dielectric, magnetic, and noble-metal layers. We selected the soft-magnetic FeSi thin film as a T-MOKE magnetic layer, while an Au thin film was chosen as a SPR-source layer, creating an FeSi-/Au-based “MO-SPR material.” Strong interactions between T-MOKE and SPR were demonstrated. When the material is irradiated with a laser beam of wavelength 660 nm, at the SPR angle to the material, θR, the highest T-MOKE value was attained. The T-MOKE was markedly enhanced at θR: ∼32 to ∼84 times higher compared with the FeSi single layer (reference). The T-MOKE was amplified by a strong interaction between MO activities and electromagnetic field distributions. The FeSi (5.0 nm)/Au (14.8 nm) specimen achieved the best signal-to-noise ratio (SNR). The sample was then tested for its sensing efficiency by measuring the T-MOKE using distilled water and a glucose solution, respectively: It was possible to distinguish between two different solutions. Our MO-SPR materials utilizing both magnetism and near-field light are thus sufficiently sensitive to be applicable as sensing materials. Furthermore, the polarity of the T-MOKE signal is flipped under the application of a small, external magnetic field owing to the soft magnetism of the FeSi T-MOKE layer. This is highly advantageous to create high-frequency AC-magnetic synchronized T-MOKE sensing systems with low-power consumption.