Enhanced Resonant Faraday Rotation in Multilayer Magnetoplasmonic Nanohole Arrays and Their Sensing Application

The optical and magnetoplasmonic properties of Ag/Co and Ag/Co/Ag multilayer nanohole arrays have been investigated. By including a top- and bottom-Ag plasmonic layer onto a Co ferromagnetic perforated film, strong extraordinary optical transmission peaks and Wood’s anomalies (transmission minima) at both film–air and film–glass interfaces of the film are observed. The coupling between plasmonics and magneto-optics in the arrays gives rise to several resonantly enhanced Faraday rotation peaks that are much sharper than the plasmonic peaks/dips. The rotation peaks appearing exactly at the transmission minima have widths as narrow as 13 nm, which are much narrower than the transmission peaks (>100 nm) and the accompanying transmission dips (∼52 nm). The narrow line width of this enhanced Faraday rotation peak allows at least 2 times enhancement of the sensing performance, which is characterized by figure of merit, in comparison to any other features of the optical transmission spectra.