Ultrahigh Figure-of-Merit in Metal–Insulator–Metal Magnetoplasmonic Sensors Using Low Loss Magneto-optical Oxide Thin Films

Achieving high figure-of-merit (defined as the ratio between refractive index sensitivity and spectral line width) in surface plasmon sensors is a fundamental quest for ultrasensitive chemical and biomedical sensing applications. Due to ohmic loss of plasmonic metal thin films, the theoretical limit of figure-of-merit is around 54 RIU–1 (refractive index unit) for Au-based plasmonic sensors at 650 nm wavelength. Here, we report a way to significantly boost the device figure-of-merit by incorporating low loss magneto-optical oxides in a novel metal–insulator–metal magnetoplasmonic sensor. Our theoretical analysis shows that a record high figure-of-merit of 39600 RIU–1 can be achieved in a simple multilayer thin film sensor device at the wavelength of 650 nm, which well exceeds that of conventional surface plasmon resonance sensors at the same wavelength. A high figure-of-merit of 964 ± 150 RIU–1 is demonstrated experimentally at 650 nm, 17.8× higher than the theoretical limit of Au surface plasmon resonanc...