Effect of annealing on magnetic properties of Fe/Fe^sub 3^O^sub 4^ soft magnetic composites prepared by in-situ oxidation and hydrogen reduction methods

Iron-based soft magnetic composites (SMCs) coated with the ferrimagnetic Fe3O4 layer have been fabricated by in-situ oxidation and hydrogen reduction methods, and then the effects of annealing process on the soft magnetic properties were investigated. It showed that the Fe3O4 insulating layer was coated on the surface of the iron powders, which effectively reduced the magnetic dilution and decreased the core loss of the composites. In addition, the Fe/Fe3O4 core-shell composites exhibited high permeability and frequency stability of permeability after annealing. The real part of permeability of the soft magnetic composites could reach a maximal value of 142.9 and a rather low core loss of 274.9 W/kg (measured at 50 mT and 100 kHz). Based on the magnetic loss separation model, the hysteresis loss and eddy current loss coefficient was obtained. It was indicated that the annealing process enhanced the eddy current loss coefficient while the hysteresis loss coefficient is close to each other for all the samples. Therefore, this work can provide a method to prepare soft magnetic composites with excellent magnetic properties and low core loss.