The preparation and magnetic performance of the iron-based soft magnetic composites with the Fe@Fe3O4 powder of in situ surface oxidation

A iron-based soft magnetic composite (SMC) has been prepared by powder metallurgy method with the Fe@Fe3O4 powder of in situ surface oxidation. Effects of the in situ surface oxidized temperature and the annealing temperature on the magnetic properties of the SMC have been investigated from 400 °C to 650 °C. The powder morphology and the phase were tested by scanning electron microscopy (SEM) and the X-ray diffraction (XRD). It shows that the surface of the iron particle contains a thin insulating layer of Fe3O4 which dramatically decreases the core loss and holds the high permeability about 100 and Bs. The mechanical properties of the bulk samples were carried out using a nanoindentation. Higher annealing temperature destroys the Fe3O4 insulating layer, resulting in the decrease of the electrical resistivity from 78.3 to 4.61 mΩ·cm as well as the magnetic permeability and its frequency stability. The coated powder can be obtained by surface oxidation at 250 °C. The SMC annealed at the temperature of 450 °C exhibits excellent magnetic and mechanical properties which is suitable for the electric-magnetic switching device, such as inductance coils, transformer cores, synchronous electric motors and resonant inductors.