Interpretation of Ferromagnetic Colloid Patterns on Ferromagnetic Crystal Surfaces

It is shown that the bodily motion of particles rather than a magneto-optic effect is chiefly responsible for field-induced changes in ferromagnetic colloid patterns on ferromagnetic crystal surfaces. A simple relation between colloid concentration and magnetic field intensity near the crystal surface is deduced from the Boltzmann distribution law. Several implications of this relation are discussed, including the role played by magnetic interaction of the particles. The formation of elongated chains of particles in a colloid placed in a magnetic field is shown to be unlikely provided that the particles are sufficiently small in size.