AC Susceptibility Measurements in the Investigation of Aggregation in Magnetic Fluids

Measurements of the complex, frequency dependent susceptibility, χ(ω)=χ '(ω)-iχ''(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, f$\text{}_{max}$, of the maximum of the loss-peaks in the χ''(ω) profiles. Corresponding calculations 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.