Experimental Study of Microwave Susceptibility in Ferrite Composite Materials

Abstract
The microwave susceptibility of NiFe₂O₄ and Co₂Z was measured between 100 and 10000 MHz. The samples were either samples with different porosities or composites with different volume fractions, in the case of NiFe₂O₄, or composites with different granulometry, in the case of Co₂Z. The measured susceptibility undergoes substantial changes at the crossover from a ceramic state to a composite of isolated particles and for different granulometries of Co₂Z in the range 10 to 600 µm. We show that a model in which the susceptibility is uniform inside the particles cannot account for these results. We suggest that in order to compute the susceptibility of composites, a microscopic approach is required.