High-frequency permeability of Fe-Co and Co granular composite materials

The relative complex permeability and permittivity spectra of Fe50Co50 (Permendur) and Co granular composite materials containing heat-treated particles have been studied in the microwave frequency range up to 20 GHz. Fe50Co50 granular composite materials have a larger relative permeability value than Co composites at the same particle content owing to the differences in the magnetizations and the magnetic anisotropies between Fe50Co50 and Co particles. Negative permeability dispersions were observed in both composites at frequencies above 6 GHz. The effect of a dc magnetic field on the permeability spectra revealed that the permeability dispersion of Co composites could mainly be attributed to the gyromagnetic spin resonance in the microwave range. From the relative permittivity spectrum, these two metal granular composites have a dielectric property even at high particle contents.