Field dependence of magnetooptic effect in magnetic colloid with superparamagnetic particles

The field dependences of magnetic birefringence in two samples of magnetic fluid with different average particle size are investigated. It is established that the dependences of magnetic birefringence are parabolic. Significant difference in experimental data and calculations using the single-particle birefringence model was found. The experimental results are interpreted by the polydispersity of the particles in the samples, as well as by the presence of small aggregates with a partially compensated magnetic moment. (paper)