Highly enhancing electromagnetic properties in Fe-Si/MnO-SiO2 soft magnetic composites by improving coating uniformity

Abstract Fe-Si/MnO-SiO2 soft magnetic composites (SMCs) are prepared by sintering ball milled Fe-Si/MnO2 core–shell structured composites. The correlation between the coating uniformity and electromagnetic properties have been investigated via adjusting ball milling parameters in detail. The results indicate that uniform MnO2 coating can be transformed into MnO-SiO2 composite coatings with high insulation due to the high temperature reaction between MnO2 and Si. Agate ball is more effective than stainless steel ball to improve the uniformity of MnO2 coating as well as the electromagnetic properties such as significantly higher resistivity, lower core loss and better frequency stability of permeability. Moreover, increasing the ball milling time from 4 h to 24 h can obviously improve the coating uniformity and thus result in the remarkable increase of the resistivity from 2.4 mΩ·cm to 356.9 mΩ·cm. And the core loss and dynamic loss decrease rapidly while the Ms shows a slight decline. When the ball milling time reaches 24 h, the Fe-Si SMCs exhibits superior magnetic properties such as high Ms (181.0 emu/g), very low core loss (361.5 kW/m3 at 100 kHz) and good frequency stability of permeability (65) from 50 Hz to 1000 kHz.