Magnetic properties of iron-based soft magnetic composites with MgO coating obtained by sol-gel method

Soft magnetic composites with a thin MgO insulating layer were produced by a sol-gel method. Energy dispersive X-ray spectroscopy, X-ray analysis, Fourier transform infrared spectroscopy, density measurement and compositional maps confirmed that thin layers of MgO covered the iron powders. Coercivity measurement showed that the stress relaxation and reduction of hysteresis loss efficiently occurred at 600 °C. At this temperature, the phosphate insulation of commercial SOMALOY^TM samples degrade and their electrical resistivity, magnetic permeability and operating frequency decreases noticeably. The results show that the MgO insulation has a greater heat resistance than conventional phosphate insulation, which enables stress-relief at higher temperatures (600 °C) without a large increase in eddy current loss. The results of annealing at 600 °C show that the electrical resistivity and ferromagnetic resonance frequency increased from 11 μΩ m and 1 kHz for SOMALOY^TM samples to 145 μΩ m and 100 kHz for the MgO insulated composites produced in this work.