MHz mechanism of permeability in Fe-Si-Al soft magnetic composites

MHz mechanism of permeability in soft magnetic composites (SMCs) based on epoxy-coated spherical Fe-Si-Al particles is studied. It is found the permeability at 1 MHz decreases from 23 (+0.69) to 10 (+0.3) and the cut-off frequency of permeability increases from 126 (+3.78) MHz to over 1 GHz with decreasing the volume fraction of particles in the SMCs from 90 % to 60 %, respectively. Combining with the results of ferromagnetic resonance, coherent rotation of domain modulated by eddy current is the dominated MHz mechanism of permeability. This is corresponding to both increase of cut-off frequency (from 31 (+0.9) MHz to 367 (+11) MHz) and decrease of loss (from 6776 (+379) kW m-3 to 1003 (+56) kW m-3 at 3 MHz) of SMCs with decreasing the average particle sizes (from 96.0 mu m to 9.3 mu m). This study deepens the understanding of the permeability of SMCs in the MHz band, and provides a reference for the design of high frequency power electronics.