On the influence of nanometer-thin antiferromagnetic surface layer on ferromagnetic CrO2 J. Appl. Phys. 112, 053921 (2012) Effect of microstructure on the electromagnetic properties of Al18B4O33w/Co and Al18B4O33w/FeCo composite particles J. Appl. Phys. 112, 053917 (2012) Ni80Fe20/Ni binary nanomagnets for logic applications Appl.Spherical, monodispersed, ferromagnetic, metallic particles of different compositions were obtained by the polyol process with a mean radius ranging from 30 nm to 1 m. The microwave permeability of metallic particles-dielectric matrix composites were studied in the range of 0.1-18 GHz. In the wide particle size range investigated, a size dependence of the dynamic permeability was observed. Whereas the permeability of micrometer-sized particles shows a single resonance band, the permeability of submicrometer-sized particles exhibits several narrow resonance bands which are shifted to high frequencies with decreasing particle size. This latter behavior was found to be in qualitative agreement with the exchange resonance modes calculated by Aharoni. That theory, however, gives an R Ϫ2 dependence on particle radius for the resonance frequency instead of the R Ϫ0.66 dependence observed experimentally.

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.

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