Complex susceptibility measurements of magnetic fluids over the frequency range 50 MHz to 18 GHz

We report on the measurement, over the frequency range 50 MHz to 18 GHz, of the complex susceptibility, chi(omega) = chi'(omega) - i chi "(omega), of a magnetic fluid as a function of the polarizing field. Measurements were obtained by means of the short-circuit transmission line technique, with the frequency range being realized by the use of an HP Network Analyser which operates up to 40 GHz. From these measurements more complete chi'(omega) and chi "(omega) profiles have been obtained, from which the values of resonant frequency, f(res), and frequency of maximum absorption, f(max), can be identified. The variation in f(max)/f(res) as a function of the polarizing field, H, over the range 0-100 kA m(-1), was investigated and found to be in accordance with that predicted by Raikher and Shliomis. The extended susceptibility profiles have enabled the normalized after-effect function of the sample, b(t)/b(0), to be investigated within the 10(-11) s time region.