Effect of microstructure on the electromagnetic properties of Al18B4O33w/Co and Al18B4O33w/FeCo composite particles.

The effect of microstructure on electromagnetic properties was investigated in Al18B4O33w/Co and Al18B4O33w/FeCo composite particles. Resistivity (ρ) and saturation magnetization (Ms) were introduced to determine the relationship between microstructure and electromagnetic properties indirectly. The ρ of Co coatings decreased by nine orders of magnitude when annealed in H2, which substantially affected permittivity and permeability. Intense dielectric relaxation occurred in 2 GHz to 18 GHz band, particularly when the ρ was lower than 1.16 × 10-3 Ω·cm, and a strong eddy current effect began to emerge when the ρ decreased to 5 × 10-4 Ω·cm. An unusual increase in the permeability of the Co coatings was identified, and enhanced exchange-coupling interaction was correspondingly revealed, which was assumed to be related to microstructure evolution. The influence of microstructure observed in Al18B4O33w/Co was further found in the Al18B4O33w/CoFe composite particles. This study suggested that the introduction of ρ and Ms was helpful in demonstrating the relationships between microstructure and electromagnetic properties. However, the quantitative characterization of microstructures and the identification of intrinsic electromagnetic parameters should be studied further. [ABSTRACT FROM AUTHOR]