Magnetic properties and loss separation mechanism of FeSi soft magnetic composites with in situ NiZn-ferrite coating

The soft magnetic performances including frequency-dependent permeability, core loss, and DC-bias properties of the Fe-6.5 wt.%Si (FeSi) soft magnetic composites (SMCs) coated with different contents of NiZn-ferrite and compacted with different forming pressures were compared and analyzed. The retained permeability at an applied field of 7960 A/m has a proportional relationship to the real part of complex permeability, which is observed to be closely related to cores' bulk density. A three-dimensional loss separation model and its related fitting analysis on the domain walls and magnetic objects were established to investigate the relative loss mechanism for the FeSi SMCs fabricated under different parameters. The variation of total core loss (P-cv) is mainly induced by the changes of hysteresis loss (P-h) and excess loss (P-exc) with different fabrication parameters, wherein both the P-h and P-exc are sensitive of the number of pinning site that inhibits the motion of domain wall. The inter-part eddy current loss is only 1/600-1/250 of total core loss for all the ferrite-coated SMCs owing to the relatively high electrical resistivity of 1.22-2.8 omega m. These results offer an in-depth observation into regulating the comprehensive soft magnetic properties of the SMCs coated with magnetic insulating layer for high-frequency and high-power applications in electromagnetic components.