Tunable magneto-optical responses in magneto-plasmonic crystals for refractive index sensing

Nanostructures with combined magnetic and plasmonic properties have become an active subject of research in recent years. However, most of magneto-plasmonic systems as biosensors adopt a complex intertwined configuration or operate in the monochrome excitation. In this work, we present a simple magneto-plasmonic system which consists of an Au nanowire array on top of a cobalt film, and theoretically demonstrate an enhanced transverse magneto-optical Kerr effect (TMOKE) of the system under the excitation of broadband light source. We study the tunable mechanism of the structure and also expound the correlation of the magnitude of the magneto-optical effect and the contrast ratio of reflection spectra, demonstrating that the high spectral contrast ratio is favorable for obtaining a giant TMOKE value with a sharp Fano-like resonance. In addition, the electromagnetic fields are strongly enhanced in the system due to the introduction of the Co layer, giving rise to high bulk sensitivities as large as 693 nm RIU⁻¹ in a wide refractive index range of 1.00–1.40. With the TMOKE measurements, we demonstrate huge values of the sensing figure of merit as large as 4192 in a saline environment. (paper)