Ferromagnetic liquids containing tin-coated iron particles of 45 A median diameter dispersed in mercury have been prepared electrolytically. After the liquids have been subjected to an abrupt stepwise reduction in an applied magnetic field the magnetization decays with a relaxation time of ∼60 s. Such long decay times cannot be explained if it is assumed that the system consists of separate particles. Long relaxation times of 60 s could arise if the particles form aggregates of approximately 104A diameter which relax by Brownian rotation when the applied field is removed. Further evidence for the the existence of 104A diameter aggregates has been obtained from an analysis of sedimentation and viscosity measurements. However, the possibility that the time dependence is due to conformational changes in the aggregates as the applied field is reduced is not ruled out and is considered a likely alternative explanation.
