AN EXPERIMENTAL-OBSERVATION OF THE DYNAMIC BEHAVIOR OF FERROFLUIDS

The frequency dependence of the complex susceptibility of eight ferrofluids have been measured. It reveals the presence of both relaxation mechanisms, Brownian and Neel, and of resonance, indicated by the real part of the susceptibility becoming negative above a critical frequency. The theoretical aspects of these mechanisms are reviewed and compared with the measured dynamical parameters. Plots of the effective relaxation time as a function of the particle radius are presented, and the relaxation time in terms of longitudinal, tau(parallel to) and transverse, tau(perpendicular to) , components are also considered and compared with measured values for tau(parallel to) determined by means of polarised measurements. The resonance data are discussed in light of the work of Raikher and Shliomis and estimates are made of the damping parameter, alpha.