Application of a paramagnetic gas theory to describe the magneto-optical response in ferrofluids

Abstract

The magneto-optical response in ferrofluids depends significantly on the orientation and intensity of an applied magnetic field. However, such essential dependence is far from being properly described by a model based on fundamental laws. In this work, the model proposed by Elmore as an extension of the Langevin theory of a paramagnetic gas is checked. Considering the ferrofluid as an ideal paramagnetic gas is not realistic, so some modifications to the model are proposed. The modified Elmore’s model adequately fits the experimental results obtained at different magnetic field intensities and orientations for the two different wavelengths used. Transmission relaxation evolution after magnetic field switch-off is also provided by the model. In addition, the results for magnetic fields parallel to the light beam are in good agreement.

Numerical calculation of ferrofluid optical transmission evolution after magnetic field switch-on

“…Therefore, light scattering in these systems is highly dependent on sizes, wavelength, chain formation and materials' refractive indices [30]. Simple ray tracing approaches found in the literature are not adequate: although they can be adapted to reflect the results, they are usually based on theories that are not completely valid for these systems [31]. On the contrary, the calculations proposed in this work attempt to simulate phenomena that do occur in the ferrofluid.…”