Magneto-optic Measurement of Fe3O4 Nanoparticle Magnetization Dynamics

J.N. Moore, M. Syed
Rose-Hulman Institute of Technology, US

Keywords: magnetism, magnetite, measurement, optic

Summary:

The magnetic response of magnetite nanoparticles in aqueous solution was investigated as a function of excitation frequency using the magneto-optic technique of AC Faraday rotation. Faraday rotation (FR) is observed as the rotation of the polarization axis of linearly polarized light as it propagates through a medium in a magnetic field applied along the direction of propagation. Solutions of varying concentration were prepared from Fe3O4 nanoparticles having an average diameter of 10 nm. Over the range of magnetic field frequencies studied, the magnitude of the Faraday rotation of these solutions was found to decrease nonlinearly with increasing frequency. The magnetization of the solutions, being proportional to the FR, follows the same trend. The measurement technique used in this experiment can detect differences in rotation less than a tenth of an arc minute in magnitude, and it is sensitive to changes in the solutions’ nanoparticle volume fractions as small as 2E-6. The work presented here investigates the magnetization phase behavior and seeks to demonstrate the sensitivity of such a technique to small changes in field frequency. The time delay in the solutions’ FR with respect to the external magnetic field was also studied.