The effect of a polarizing magnetic field on the dynamic properties and the specific absorption rate of a ferrofluid in the microwave range

Abstract

ABSTRACT Measurements are presented of the frequency and field dependent, complex magnetic permeability, μ(f, H) = μ′(f, H)-i μ″(f, H), of a kerosene-based ferrofluid sample with magnetite particles, over the frequency range, f, of 0.4–6 GHz, and polarizing field, H, range of 0–102 kA/m. In this frequency range, both the ferromagnetic resonance at a frequency, f res , and the corresponding maximum absorption at a frequency, f max , were determined. From the H dependence of both f res and the ratio of f max /f res , we determined the anisotropy field, H A , the anisotropy constant K eff , the gyromagnetic ratio, , the damping parameter, , the spectroscopic splitting factor, g, and the internal magnetic viscosity, . Also, the theoretical Néel relaxation time, , was evaluated. Furthermore, the measurements of, μ(f), enabled one to study the effect of, H, on the the specific absorption rate, SAR, and the time dependence of the variation in temperature, ΔT, of the investigated ferrofluid sample. The SAR was calculated, using a new equation for the calculation of the SAR of ferrofluids. This equation offers a more precise computation of the SAR in that it takes into account the density of the ferrofluid ρ F , as opposed to using just the density of the dispersed solid particles, ρ S . These results illustrate how control of the SAR and the variation in ΔT, of the ferrofluid sample, through the variation of H, and has applications in the treatment of cancer by magnetic hyperthermia, for modeling bio-heat transfer phenomena, microwave heating or the possibility of use of the ferrofluid as a shield material against microwave electromagnetic radiation. Also, knowledge of the magnetic parameters of ferrofluids, is useful in the design and manufacture of some microwave devices.