Enhanced permeability and reduced loss in FeSiAl soft magnetic composites via phosphating and ferrite coating

FeSiAl soft magnetic composites (SMCs) are promising candidates for high-frequency power electronics in 5 G communication and electric vehicles, but their performance is limited by brittle phosphate coatings and difficulties in ferrite integration. In this work, we systematically optimized phosphating concentration and explored two Ni-Zn ferrite coating strategies. Gradient experiments identified 0.2 wt% phosphating as optimal. The physically blended ferrite coating exhibited superior performance compared to the in-situ chemical method, delivering high permeability (μₑ≈180), excellent frequency stability (Δμ<5 % in 10 kHz–1 MHz) and low power loss (165.26 mW/cm³ @50 kHz, 100 mT). Microstructural and magnetic characterizations, together with loss separation analysis, confirmed that the improvements originated from preserved insulation integrity and suppressed eddy currents. This study provides a scalable route for developing high-performance FeSiAl SMCs for next-generation power electronics.