The influence of the dielectric on the properties of dielectromagnetic soft magnetic composites. Investigations with silica and silica hybrid sol–gel derived model dielectric

Dielectromagnetics made from organic–inorganic hybrid silica-coated iron powders were characterised by determination of their physical, mechanical and magnetic properties. The influence of three main factors, dielectric composition, addition level and heat treatment conditions were investigated. Results showed that these factors have significant effects on the performance of the dielectromagnetics. Increase in the organic phase content in these dielectric coatings tends to increase both the electrical resistivity and magnetic permeability of dielectromagnetics, although the strength and density are slightly impaired. Increasing the coating thickness leads to improvements in resistivity and thus reduced eddy current losses, but these are offset by reductions in density, strength and particularly magnetic permeability. A hybrid organic–inorganic coating formulation based on 40 mol% MTMS and 60 mol% TEOS precursors was found to be the optimum composition investigated. Addition levels between 0.1% and 0.3% were found to offer a good compromise between maximum permeability (μmax>400) and minimum loss (typically <8 W/kg) for operation at 50 Hz/1 T, and the system can be optimised within this range for the desired performance.