Design and evolution of Fe–Si–Al soft magnetic composites doped with carbonyl iron powders: Overcoming the restrictive relation between permeability and core loss

Herein, Fe–Si–Al-based soft magnetic composites (SMCs) doped with carbonyl iron powders (CIPs) at different concentrations were successfully prepared. The reaction between CIPs and core–shell Fe–Si–Al/SiO2 heterogeneous composite powders, induced by the high temperature and concentration gradient during heat treatment, was investigated. The effect of doping CIPs at different concentrations on the microstructure and magnetic properties of Fe–Si–Al-based SMCs was also studied. During heat treatment, the Fe–Si–Al/SiO2 powders inside the SMCs exhibited a complex reaction with the doped CIP. The reaction involved multidirectional migration of Al and Si, evolution of an Al2O3 + SiO2-composite insulating layer and formation of composite ferromagnetic phases. Furthermore, the density, saturation magnetisation, permeability and core loss of Fe–Si–Al-based SMCs were improved by doping the composites with moderate amounts of CIPs. The Fe–Si–Al-based SMCs doped with 8-wt% CIPs exhibited the best comprehensive magnetic properties (permeability = 43.5, saturation magnetisation = 160.1 emu/g and core loss = 481.7 kW/m3 at 10 mT and 100 kHz). Compared with undoped Fe–Si–Al-based SMCs, the permeability and saturation magnetisation increased by 40.3% and 24.0%, respectively, and the core loss decreased by 18.8%. Thus, the proposed method can effectively address the restrictive relation problem between permeability and energy loss in these composites.