Longitudinal magneto-optical effect of ferrofluids

Abstract

The authors' aim is the measurement of the ferrofluids' Faraday effect, with a low magnetic field applied (between 0 and 500 G) and various volumic magnetic concentrations. For each of them, they measured the value of the minimum longitudinal magnetic field applied, causing a self-developing phase transition (appearance of clusters). This leads to the lessening or cancelling of the transmitted light beam. A dynamic study of this effect has been made (by switching on and off the magnetic field applied to the ferrofluid) that carried out a large asymmetry. An automated (by means of microprocessor and stepping motor) polarimetric device was developed to allow a quick measurement of the Faraday rotation alpha _F versus the magnetic field applied. The precision is 0.01 degrees and the measuring time is F of the ferrofluid in the homogeneous state for any value of H. The graph of alpha _F=f(H) at lambda =663 nm and 5 different concentrations is given.