ON THE INFLUENCE OF INERTIAL EFFECTS, ARISING FROM ROTATIONAL BROWNIAN-MOTION, ON THE COMPLEX SUSCEPTIBILITY OF FERROFLUIDS

This paper reports on the use of the autocorrelation function of the m agnetization decay of a ferrofluid to investigate the effects which th e moment of inertia of single domain ferromagnetic particles have on t he frequency dependent complex susceptibility, chi(omega)=chi'(omega)- (i) chi ''(omega), of ferrofluids. The contribution of particle inerti al effects, arising from rotational Brownian motion, to an apparent re sonance, indicated by the real component, chi'(omega), going negative at a frequency lower than that predicted by theory, is investigated. T he Langevin treatment of Brownian motion is used to incorporate therma l agitation into the analysis.