Linear dichroism and birefringence effects in magnetic fluids

The purpose of the paper is to explain the linear birefringence and dichroism observed in magnetic fluids when subjected to a magnetic field. Linear aggregates of nanosize near spherical particles, which are considered to be responsible for these phenomena, have been analyzed in terms of the classical oscillating dipole model where each particle is treated as a simple dipole under the action of the electric field of a light beam. The analysis is produced in terms of the number of particles in the aggregate for both spherical and slightly nonspherical particles. Optical anisotropy factors and expressions for the magnetic-field dependence of the birefringence and dichroism due to preexisting aggregates are given. Numerical calculations have been carried out for ${\mathrm{Fe}}_{\mathrm{3}}{\mathrm{O}}_{\mathrm{4}}$ particles. Finally, the formulae are applied to experimental data where a close fit is obtained.