Preparation of Fe-based soft magnetic composites with high Bs by acidic bluing coating

Fe-based soft magnetic composites (SMCs) are technologically important due to their unique properties such as satisfactory magnetic performance and low loss for high frequency applications. Insulation coating of the ferromagnetic powders is critical in the preparation of SMCs. While traditional phosphate treatment allows surface passivation of the Fe powders, the obtained phosphate coating layers are non-magnetic, resulting in decreased saturation magnetization. Consequently, it is essential to develop SMCs with both high flux density and low loss. In this work, acidic bluing method has been used to grow Fe₃O₄ layers as insulation coating on the surfaces of iron powders. As Fe₃O₄ is a ferromagnetic material with high electrical resistivity, the effect of magnetic dilution can be avoided.