BROAD-BAND MEASUREMENT OF THE COMPLEX SUSCEPTIBILITY OF MAGNETIC FLUIDS

We report on the measurement, over the frequency range 10 Hz to 3 GHz, of the complex susceptibility, chi(omega) = chi'(omega) - ichi''(omeg a), of a magnetic fluid with manganese ferrite particles of median dia meter 9.4 nm in a hydrocarbon carrier. This upper frequency was realiz ed by use of a HP Network Analyser which operates over the frequency r ange 300 kHz to 3 GHz and has enabled a more complete susceptibility-f requency profile to be determined. The presence of a loss-peak at 30 M Hz in the chi''(omega) component is a demonstration of the phenomenon of superparamagnetism in small ferromagnetic particles whilst the tran sition of chi'(omega) to a negative value at 65 MHz is indicative of f erroresonance.