Determination of maximum particle size in magnetic fluids

Higher-order moments of particle size distribution functions are determined for magnetic fluids from analysis of initial segments of magnetization curves. It is shown that the higher-order moments calculated using approximation of real particle size distributions by the I" distribution are strongly overestimated. Agreement between the measured and calculated moments can be radically improved by truncating maximum particle size X (max). A relation between X (max) and the parameters of the I" distribution is proposed taking into account the degree of polydispersity of a magnetic fluid. Namely, the ratio between the maximum and most probable particle diameters is equal to the ratio between the mean-square magnetic moment of a particle and its squared average magnetic moment.