Evidence of birefringence due to two phases in the magnetic fluid film

The angle Δη made by the principal axis of the transmitted elliptical polarization with respect to the incident linear polarization was measured to study the birefringence effect of a magnetic fluid film under a magnetic field H parallel to the plane of the film. When varying the angle θ span by H with respect to the incident linear polarization, the Δη was found to be a symmetric function of θ with a relative maximum at θ around 45°. This Δη-θ relation was found for the first time and a theoretical two-phase model is developed to clarify the mechanism of the birefringence effect of ferrofluids.