AC SUSCEPTIBILITY MEASUREMENTS IN THE INVESTIGATION OF AGGREGATION IN MAGNETIC FLUIDS

Measurements of the complex, frequency dependent susceptibility, χ(ω) _ x'(ω)—ix"(ω) of two water based magnetic fluids, over the frequency range 10 Hz to 1 MHz are reported. Plots of the susceptibility components against log[f (Hz)] are found to have approximate Debye-type profiles with the presence of Brownian relaxation being indicated by the frequency, fmax, of the maximum of the loss-peaks in the χ"(') profiles. Corresponding calcu -lations of particle hydrodynamic radius indicate the presence of aggregation. Frohlich, normal and lognormal distribution functions are used to obtain an estimate of the aggregate size distribution in the samples.