Microstructure and magnetic properties of MnO2 coated iron soft magnetic composites prepared by ball milling

Abstract In this paper, Fe soft magnetic composites (SMCs) coated with MnO2 were prepared successfully by ball milling and following spark plasma sintering. The effect of MnO2 content on microstructure and magnetic properties for the Fe/MnO2 SMCs was investigated in detail. The analysis results show that a uniform MnO2 coating layer can be formed on the surface of the Fe particles via low speed ball milling with agate balls. When the MnO2 content increases from 0.0 wt% to 10.0 wt%, the thickness of the MnO2 coating layer exhibits a growth trend. As a consequence, the increased nonmagnetic phase leads to the magnetic dilution, finally resulting in the reduced saturation magnetization and deteriorated coercivity. Moreover, the enhanced resistivity induced by the increased thickness, significantly reduces the generation of the inter-particle eddy current, which leads to more stable permeability and lower total core loss at high frequencies. This study provides a novel insulating coating layer to reduce total core loss and is advantageous for the development of iron-based SMCs.