Enhanced magnetic properties of Fe soft magnetic composites by surface oxidation

Fe soft magnetic composites (SMCs) with low core loss were fabricated via surface oxidation of the Fe powders by H2O and O-2 at elevated temperatures. Surface oxidation prevents magnetic dilution due to the formation of the ferromagnetic iron oxide coating layer, giving rise to high magnetic flux density and effective permeability of the SMCs compared with those fabricated with traditional phosphate coating. Mechanism of the oxidation process has been investigated where Fe3O4 forms by reactions of Fe with H2O and O-2. The Fe3O4 coating layer tends to convert into gamma-Fe2O3 with increased oxidation temperature and time. By controlling composition of the coating layer, low core loss of 688.9 mW/cm(3) (measured at 50 riff and 100 kHz) and higher effective permeability of 88.3 can be achieved for the Fe SMCs. (C) 2015 Elsevier B.V. All rights reserved.