PREPARATION AND MICROWAVE CHARACTERIZATION OF SPHERICAL AND MONODISPERSE CO20NI80 PARTICLES

Spherical and monodisperse Co20Ni80 particles were prepared, in the micrometer and submicrometer size range, by the polyol process. X-ray diffraction showed crystalline particles with a fcc structure. From electron probe microanalysis a fairly homogeneous distribution of both elements within each particle was observed. Microwave properties of metal particles dielectric matrix composites were studied in the 0.1-18 GHz range for different filler concentrations. The intrinsic permeability of the metal powders was obtained using the Bruggeman effective medium theory. The control of the particle size allowed the study of its effect upon dynamic permeability. Whereas micrometer size particle permeability presents a single resonance band at low frequencies which can be correlated to the low magnetocrystalline anisotropy of the particles, submicrometer size particle permeability exhibits an original behavior, never reported before, with several resonance bands.