Biasing field effect on the microwave dielectric properties of magnetic fluids

A theory is presented which shows the biasing field effect on the frequency dependence of the complex dielectric permittivity of magnetic fluids, as measured with a coaxial cell having the axis perpendicular to the biasing field. The theory is supported by measurements on a kerosene based magnetic fluid with magnetite particles, subjected to a biasing field, H of up to 168 kA/m, over the frequency range 0.1–6 GHz. A decrease in the frequency corresponding to the maximum of ε″(ω) and of an increase in both ε′(ω) and ε″(ω) with increasing H was found.