EXPERIMENTAL AND THEORETICAL PROFILES OF THE FREQUENCY-DEPENDENT COMPLEX SUSCEPTIBILITY OF SYSTEMS CONTAINING NANOMETER-SIZED MAGNETIC PARTICLES

Measurements of the frequency-dependent complex susceptibility chi(ome ga)= chi'(omega) = i chi ''(omega) of ferrofluids and magnetic tape ar e presented and compared with susceptibility profiles generated by mea ns of classical models. In the case of ferrofluids, fitting is realize d by means of a combination of the equations of Raikher and Shliomis a nd of Debye. These equations are for monodispersed particles, and as f errofluids consist of polydispersed particles, it is demonstrated that to achieve a good fit to the experimental data it is necessary to pro vide for both a distribution of particle radii r and anisotropy consta nt K. In terms of the parallel, chi(parallel to)(omega), and transvers e, chi(perpendicular to)(omega), components of the susceptibility, it is shown that the incorporation of a distribution of particle radii is required to fit the parallel component chi(parallel to)(omega) of the susceptibility, while a distribution of anisotropy constants is requi red to fit the resonant chi(perpendicular to)(omega) component. Suscep tibility data for magnetic tape are fitted to the equations of Landau and Lifshitz, suitably adapted to provide for a distribution of K alon e. The usefulness of the fitting technique in ascertaining average val ues of the damping parameter alpha and anisotropy constant K is demons trated.