The Ellipticity Measurements-Determination of the Size of Superparamagnetic Core of Magnetic Metal Nanoparticles

Ferrofluids, i.e., suspensions of magnetic nanoparticles, find numerous applications in biomedicine, catalysis, and optical technologies. In this work we introduce a novel and easy-to-handle way of measuring the diameter of the unoxidised core using the Faraday effect and the induced ellipticity of the light. The effects are based on the optical activity of material induced by magnetic field parallel to the direction of the propagation of the laser beam. For the spherical superparamagnetic inclusions (nanoparticles) suspended in a diamagnetic medium a theoretical model is applied. It enables one to determine the magnetic momentum of a single nanoparticle, and thus its diameter that is in coincidence with the statistical analysis of transmission electron microscopy images.