Observation of the Sagnac Effect in the Magnetization of Magnetic Nanoparticles in Water

A square optical loop used to observe the Sagnac effect was constructed by using a 632.8-nm He-Ne laser, a polarizing beam splitter and three mirrors, combined with a detection system. When a magnetic field was applied from the transversal direction to the beam of the loop, which passed through the sample cell containing magnetic nanoparticles (MNPs) in water, Sagnac interference was observed depending on the concentration of MNPs, indicating evolution of the magnetic birefringence. A possible analytical use of the magnetic Sagnac effect has been suggested.