Microstructure and magnetic properties of layered Fe soft magnetic composites with magnetic insulating layer

Designing magnetic insulation coatings remains a challenge for high-performance soft magnetic composites (SMCs). In this study, the layered Fe SMCs with magnetic insulating layer were fabricated through ball milling, and pressing processes. The impacts of NiZnFe2O4 content on the structure and electromagnetic properties of the Fe SMCs were investigated. The results showed that a uniform NiZnFe2O4 insulating layer was formed on the surface of flaky iron powder during the ball milling process, and the layer thickness increased with the NiZnFe2O4 content. As the NiZnFe2O4 content increased from 0 wt% to 12.5 wt%, the saturation magnetization of the Fe/NiZnFe2O4 composite particles decreased linearly, indicating precise control over the insulating layer. Concurrently, the frequency stability of the magnetic permeability of the Fe SMCs was progressively augmented. Owing to the low demagnetization factor of the flaky Fe powders in the in-plane direction, demagnetization effect was effectively reduced in the layered Fe SMCs, and they exhibited a high permeability. The magnetic loss increased initially and then decreased with increasing NiZnFe2O4 content, while excessive nanoparticle agglomeration led to increased hysteresis and excess losses. The Fe SMCs with 5.0 wt% NiZnFe2O4 content demonstrated superior performance with high saturation magnetization (193 emu/g), good frequency stability of permeability, and low magnetic loss (590 W/kg at 0.05 T/50 kHz). This study provides new insights into the design of magnetic insulation layers for soft magnetic composites and lays the foundation for the development of high-frequency magnetic materials.