Experimental study of magnetic interactions between colloidal particles in magnetic fluids

In order to clarify whether or not there is any magnetic interaction between the magnetic colloidal particles in magnetic fluids (MFs), we present a method for comparing the magnetization curve of a mother MF with that of a few-thousand-fold diluted solution. For a MF which showed clusters of colloidal particles in an optical microscope under an applied magnetic field, the hysteresis loops for the mother MF and its few-thousand-fold dilution displayed different shapes for weak fields. We conclude from this result that strong magnetic interactions exist between the particles in this MF. On the contrary for a MF which showed no clusters under optical microscopy, no differences in shapes of the hysteresis loops for the mother MF and its few-thousand-fold dilution were observed in the weak field region. However, differences were observed for the field region above 80 kA/m. (C) 2002 American Institute of Physics.