Magnetic properties and loss mechanism of Fe-6.5wt%Si powder core insulated with magnetic Mn-Zn ferrite nanoparticles

The Mn-Zn ferrite nanoparticles with a spinel structure were successfully prepared by using chemical co-precipitation method. The formed magnetic ferrite particles were coated on the surface of Fe-6.5 wt%Si alloy particles with the epoxy resin to prepare the powder core. The influence of magnetic ferrite insulation on the magnetic properties of the powder core was studied. Insulating with a moderate quantity of ferrite was found to improve the effective permeability and the loss of the powder core, while the inadequate insulation and the excessive insulation with ferrite led to the rapid growth of the eddy-current loss at high frequency and the remarkable decrease of the effective permeability, respectively. The effective demagnetizing field determined by the core's density and the magnetic nature of the ferrite were proposed to be the main causes of the variation of the core's magnetic performance. Loss separation fitting revealed that the hysteresis loss is much higher than the eddy-current loss for the core measured at the frequency lower than 120 kHz. This suggested that improving the effective permeability and the loss of the powder core in low-frequency range should focus on the means of reducing the effective demagnetizing field.