EXPERIMENTAL-STUDY OF MICROWAVE SUSCEPTIBILITY IN FERRITE COMPOSITE-MATERIALS

The microwave susceptibility of NiFe2O4 and Co(2)Z was measured betwee n 100 and 10000 MHz. The samples were either samples with different po rosities or composites with different volume fractions: in the case of NiFe2O4, or composites with different granulometry, in the case of Co (2)Z. The measured susceptibility undergoes substantial changes at the crossover from a ceramic state to a composite of isolated particles a nd for different granulometries of Co(2)Z in the range 10 to 600 mu m. We show that a model in which the susceptibility is uniform inside th e particles cannot account for these results. We suggest that in order to compute the susceptibility of composites, a microscopic approach i s required.