Magneto-dielectric properties of transformer oil based magnetic fluids in the frequency range up to 2 MHz

M. Timko¹ - K. Marton² - L. Tomco³ - J. Kiraly² - M. Molcan¹ - M. Rajnak¹ - P. Kopcansky¹ - R. Cimbala² - F. Stoian⁴ - S. Holotescu⁴ - A. Taculescu⁵

¹ Institute of Experimental Physics, Slovak Academy of Sciences, Kosice, Slovakia
² Faculty of Electrical Engineering and Informatics Technical University in Kosice, Kosice Slovakia
³ Faculty of Areonautic, Technical University in Kosice, Kosice, Slovakia
⁴ Politehnica University of Timisoara, Timisoara 300222, Romania
⁵ Laboratory of Magnetic Fluids, Romanian Academy -- Timisoara Division, Timisoara, Romania

Abstract
We have studied dielectric and magnetodielectric properties of transformer oil UTR 40 based magnetic fluid with various concentrations of magnetic nanoparticles of Fe₃O₄ covered with oleic acid as a surfactant. The experiments were conducted at different volume concentrations of magnetite nanoparticles at room temperature and in a frequency range from 100 Hz up to 2 MHz with and without external magnetic field up to 30 mT. The quasilinear increase of the dielectric constant with volume concentration has been confirmed. The variation in dielectric permittivity with frequency reveals that the dispersion exhibited by the samples is due to a Maxwell-Wagner type interfacial polarization. The dielectric anisotropy factor g(B,ω) is very close to g=1. Tables 1, Figs 7, Refs 14.