Plasmon Enhanced Faraday Rotation in Fe3O4/Ag Ferrofluids for Magneto Optical Sensing Applications

The magnetic/metallic nanocomposites are special intelligent materials and find many applications in photonics, magneto-optical devices, and biosensors. This paper introduces the synthesis and performance of Fe₃O₄/Ag ferrofluids using a facile one-step modified co-precipitation method. The nanocomposites were characterized using X-ray diffraction, scanning electron microscopy, XPS, and Fourier transform infrared spectra for structure, morphology, and component investigation, respectively. The viscosity, stability, magnetic, and magneto-optical properties of the ferrofluids were measured through the vibrating sample magnetometer, Faraday rotation optical bench, and viscosity tester. Fe₃O₄/Ag-based ferrofluids demonstrated good stability (did not agglomerate for 120 h), big magnetic field-dependent-viscosity, surface plasmon resonance effect, superpagamagnetic nature, and improved Faraday effect; these characters are good for MO sensing application. The Verdet constant of ferrofluids at 633 nm increased from 5.66 to 8.53 × 10⁻² deg/G cm after Ag coating on Fe₃O₄.