Fe-Si-Al soft magnetic composites were composed of gas-atomized Fe-9.6wt.%Si-5.4wt.%Al alloy powders insulated
with silica nanoparticles. The influence of silica insulation content on the core’s magnetic properties was
studied. It was found that increasing the silica mass ratio deteriorated the effective permeability and core loss in
the frequency range of 40-120 kHz, while improved the quality factor at 100 kHz and DC-bias performance.
The effective demagnetizing field reflected by density and the core’s volume resistivity may cause the variations
of these magnetic parameters. Loss separation fitting was performed using the Bertotti formula, indicating that
silica insulation increased the hysteresis loss and reduced the eddy-current loss. The hysteresis loss took over at
the frequency lower than 120 kHz in this work. With increasing the frequency, the eddy-current loss grew more
quickly than the hysteresis loss. Therefore, different methods should be adopted to reduce the core loss according
to the core’s application frequency.