Equilibrium magnetization of concentrated ferrocolloids

A number of experiments were performed to investigate the temperature and concentration dependences of the initial susceptibility of magnetite ferrocolloids. Measurements were taken at infralow frequency of 0.05 Hz in a wide range of temperatures and concentrations. The experimental results provide verification of different theoretical models dealing with the equilibrium magnetization of ferrocolloids and taking into account magneto-dipole interparticle interactions. The limits of application for the models were qualified. It was shown that mean-spherical and high-temperature approximations provide adequate description of the real ferrocolloids. The Weiss model has been found to give satisfactory results only for diluted and moderately concentrated ferrocolloids, and, as well, in the region of strong magnetic fields.