AN EXPERIMENTAL-OBSERVATION OF THE DYNAMIC BEHAVIOR OF FERROFLUIDS

The frequency dependence of the complex susceptibility of eight ferrof luids have been measured. It reveals the presence of both relaxation m echanisms, Brownian and Neel, and of resonance, indicated by the real part of the susceptibility becoming negative above a critical frequenc y. The theoretical aspects of these mechanisms are reviewed and compar ed with the measured dynamical parameters. Plots of the effective rela xation time as a function of the particle radius are presented, and th e relaxation time in terms of longitudinal, tau(parallel to) and trans verse, tau(perpendicular to) , components are also considered and comp ared with measured values for tau(parallel to) determined by means of polarised measurements. The resonance data are discussed in light of t he work of Raikher and Shliomis and estimates are made of the damping parameter, alpha.