Theory of the Optical and Magnetic Properties of Ferromagnetic Suspensions

Abstract

The theory of the optical transparency of ferromagnetic suspensions, as modified by magnetic fields, is developed along lines suggested by C. W. Heaps. It is proposed to determine the average "shape" of the particles by measuring the transmission of a suspension in various directions while the particles are magnetically aligned parallel to one another. From this information, the complete magneto-optic behavior of the suspension can be deduced; comparison between experimental and theoretical curves gives a value of the (average) magnetic moment of the particles. In addition, theory for two new magneto-optic experiments is developed, one which will give directly the intensity of magnetization of the particles, the other which will give directly the volume of the particles. In the first experiment changes in transparency are used to indicate when the particles have been rotated magnetically through a definite angle; the second experiment is based on the changes in transparency accompanying the return to random particle orientation following the removal of an applied magnetic field. It is shown that suspensions should have a transmission of ($\frac{1}{e}$) to give a maximal magneto-optic effect.