Magneto-dielectric spectroscopy of magnetic fluids

C. N. Marin¹ - P. C. Fannin² - K. Raj³ - V. Socoliuc^{4, 5}

¹ West University of Timisoara, Faculty of Physics, no. 4, V. Parvan Blv., 300223, Timisoara, Romania
² Department of Electronic and Electrical Engineering, Trinity College, Dublin 2, Ireland
³ Ferrotec Corporation, Bedford, NH, USA
⁴ Petru Poni Institute of Macromolecular Chemistry, 41A Grigore Ghica Voda Alley, 700487 Iasi, Romania
⁵ Romanian Academy -- Timisoara Branch, Center for Fundamental and Advanced Technical Research, Romania

Abstract
Transmission line techniques have been used to determine both the frequency f(ω/2π) and the polarized field dependence H of the complex magnetic susceptibility, χ(ω,H) = χ′(ω,H) − iχ^′′(ω,H), and the complex dielectric permittivity, ε(ω,H) = ε′(ω,H) − iε^′′(ω,H), of magnetic fluids over the ranges 100 MHz to 6 GHz and 0 to 125 kA/m, respectively. Examples are given on how χ(ω,H) measurements may be used in the evaluation of the magnetic properties of magnetic fluids and how ε(ω,H) measurements can be used to assess their colloidal stability. It is shown that if ε′(ω,H) increases with the increase of H, the magnetic fluid has a good colloidal stability, and if ε′(ω,H) decreases with the increase of H, the magnetic fluid has drop-like particle agglomerations. The technique is validated by light scattering investigations. Figs 4, Refs 11.