FREQUENCY OF FERROMAGNETIC-RESONANCE IN FERROFLUIDS

In the measurement of the complex susceptibility, (chi)(omega)=(chi)'( omega)-i(chi)''(omega), of ferrofluids, resonance is indi cated by a t ransition in the value of (chi)'(omega) from a +nu e to a -nu e quanti ty. Here the complex susceptibility measurements, over the frequency r ange 0.1 to 6 GHz, of four colloidal samples, three of which display t his resonant phenomenon, are presented. It is found that the experimen tally determined resonant frequency is lower than that predicted by cl assical theory. This discrepancy is examined in the light of the work of Raikher and Shliomis. The presence of a pronounced loss peak in the (chi)''(omega) component of one of the samples, in the 320 MHz region , is interpreted as being a demonstration of the phenomenon of superpa ramagnetism.