Colloidal crystals in magnetic fluid

Abstract

Monodispersed polystyrene spheres with diameters in the μm range are mixed with magnetic fluid and confined to thin layers between two glass plates. In an external magnetic field H, polarization of the magnetic fluid produces an apparent magnetic moment Mv associated with each sphere due to the displaced volume V. For low fields, Mv=−VχeffH, where χeff is the effective volume susceptibility of the fluid. For fields parallel to the layer, there is an apparent attractive dipolar interaction between the spheres producing long chains. By applying fields normal to the layer, the spheres behave as repulsive dipoles forming triangular lattices. This offers a novel model system for studies of phase transition phenomena. The direct visual observation of the collective behavior of such spheres will be presented.