120 °C Si-O insulating shell formation on iron nanoparticles synthesized from micron-size magnetite by gas-solid reaction

In this study, Fe-based alloy nanopowders were subjected to gas-solid reactions at different temperatures to form ultrathin insulating shells on magnetic particles. The resulting samples were then characterized in terms of their structure, magnetic properties, and electrical properties. Oxidation at a very low temperature of 120 °C enabled the synthesis of bcc-Fe nanoparticles with 40 nm coated with a 5 nm-thick Si-O shell. The nanopowder with insulating shell increases the effective resistivity by approximately one order of magnitude while limiting the reductions in effective saturation magnetization and coercivity to about 10 % and 2 %, respectively. Furthermore, this study demonstrates that insulated nanoparticles exhibit not only conductive and magnetic properties but also a non-negligible capacitive property. Therefore, the effective permittivity obtained this study is expected to be useful for accurately modeling and analyzing the response of electromagnetic conversion devices employing such magnetic powder cores.