Optical and Magnetic Properties of a Magnetite Suspension

Abstract

A suspension of magnetite powder in oil acts in a limited way as a light shutter. When a magnetic field is parallel to the light direction more light is transmitted than when the light is transverse. Microscopic examination shows that the particles form elongated groups. Each particle is probably a single magnetic domain, magnetized to saturation, and hence it attracts neighboring particles. The theory of the phenomenon, assuming the groups to be uniform and cylindrical, gives an equation for the amount of transmitted light in terms of magnetic field strength. This equation is subjected to experimental test and is not well verified. The magnetization curve of a dense suspension is determined experimentally and found to fit the Langevin curve fairly well. The group of particles, constituting the magnetic element, has an intensity of magnetization considerably less than the saturation value, although the individual particles are probably single, saturated domains.