Microwave dielectric properties of magnetite colloidal particles in magnetic fluids

Abstract

Measurements performed over the frequency range 700 MHz to 3 GHz, of the complexdielectric permittivity of (i) a kerosene-based magnetic fluid sample with magnetiteparticles stabilized with oleic acid, (ii) oleic acid and (iii) kerosene, are presented.The biphasic dielectric model describing the dielectric behaviour of magnetic fluids wasredefined based on the experimental results of Rocchiccioli-Deltcheff et al. According tothis proposed new model, the magnetic fluids can be considered as being biphasic systemsin which one phase consists of surfacted colloidal particles electrically charged byadsorbed or chemisorbed ions and the other phase consists of the carrier liquid.Using the Sillars theory for heterogeneous dielectrics, in the biphasic approximation, wehave determined the dielectric permittivity, electric conductivity and shape factor of thecolloidal magnetite particles within the investigated magnetic fluid, in the microwave range.The values obtained for the colloidal magnetite particles are the shape factorn = 2.27, the real part of the dielectric permittivityε1′ = 36.8, and the effectiveconductivity σ1 eff = 1.5 Ω−1 m−1.The differences between the experimental results and the values of conductivity andpermittivity of bulk magnetite are explained in terms of the proposed biphasic model.