Percolation in magnetic composites

Electric and magnetic properties of composite materials consisting of low density polyethylene filled with powdered ferromagnetic materials were investigated(double dagger). The volume fractions of the fillers were varied from 10% up to the theoretical maximum packing fractions, i.e. between 0.70 and 0.77, so that the percolation phenomenon could be investigated. The ferromagnetic fillers used were HyMu 800 (a nickel-iron-molybdenum alloy), MnZn ferrite and NiZn ferrite. The particle sizes and size distributions of the fillers were well characterized by image analysis techniques. Based on the particle size distribution the maximum loading levels of fillers as permitted by geometric considerations were calculated. The properties of the composites characterized included: volume and surface resistivities, dielectric constants, electrical loss factors and magnetic permeabilities.