Influence of heat treatment on microstructures and magnetic properties of Fe-based soft magnetic composites prepared by co-precipitation method

Fe/(NiZn)Fe2O4 soft magnetic composites (SMCs) were prepared by the co-precipitation method using pure atomised iron powder and chloride as raw materials. The morphology and element content of coated powders were analysed using scanning electron microscopy and energy dispersive spectroscopy. Moreover, we used electron probe micro-analyser, X-ray diffraction and Raman spectrum to systematically investigate the effect of heat treatment temperature in argon on the microstructure of SMCs, including O element distribution, phase formation and internal stress. The results show that by increasing heated temperature, the oxygen content at the boundary of the SMCs increased and the internal stress release of SMCs was more complete. Moreover, nonmagnetic FeO would be generated in SMCs when the heat treatment temperature reached 550 degrees C. We also discussed the relationship of heat treatment temperature and atmosphere with AC magnetic properties of the samples, including permeability, core loss and coercivity. The results indicate that the SMCs annealed at 450 degrees C in argon had the optimum magnetic performance (mu= 55.8, P-cv = 12.2 kw/m(3), H-c = 22.6 A/m). At the heat treatment temperature of 500 degrees C, the argon-annealed samples presented better magnetic properties and higher frequency stability than air-annealed samples.