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 diameterof the unoxidised core using the Faraday effect and the induced ellipticity of the light. The effects are basedon the optical activity of material induced by magnetic field parallel to the direction of the propagation of thelaser beam. For the spherical superparamagnetic inclusions (nanoparticles) suspended in a diamagnetic mediuma theoretical model is applied. It enables one to determine the magnetic momentum of a single nanoparticle, andthus its diameter that is in coincidence with the statistical analysis of transmission electron microscopy images.