Formation mechanism and enhanced magnetic properties of Fe–Si/Fe2SiO4 soft magnetic composites transformed from Fe-6.5 wt%Si/α-Fe2O3 core-shell composites

Abstract

In this work, Fe–Si/Fe2SiO4 soft magnetic composites (SMCs) are prepared successfully via sintering Fe-6.5 wt%Si/α-Fe2O3 core-shell composite powders obtained by ball milling. The transformation mechanism from Fe-6.5 wt%Si/α-Fe2O3 to Fe–Si/Fe2SiO4 is revealed in detail. The effect of α-Fe2O3 coating content on microstructure and magnetic properties for the Fe–Si/Fe2SiO4 SMCs is also investigated. During the high temperature sintering process, α-Fe2O3 coating will in situ react with diffused Si from Fe–Si alloy cores, and result in the generation of Fe2SiO4 insulating layer and Fe atoms. When the α-Fe2O3 coating content increases from 0.0 wt% to 7.5 wt%, the insulating layer becomes thicker. Nevertheless, with further increasing the α-Fe2O3 coating content from 7.5 wt% to 12.5 wt%, the generation of excessive Fe breaks the continuity of the insulation layer. As a result, the saturation magnetization decreases gradually, while the coercivity exhibits an opposite trend. The core loss decreases firstly and then increases. Therefore, the Fe–Si/Fe2SiO4 SMCs coated with 7.5 wt% α-Fe2O3 exhibit superior comprehensive performance such as very low core loss (39.6 mW/cm3 at 50 kHz), very high saturation magnetization (191.4 emu/g) and stable permeability (44) from 50 Hz to 200 kHz.