Enhanced AC magnetic properties of Fe-based soft magnetic composites coated with an electrically insulated SiO2–ZrO2 layer

Insulating Fe@SiO2–ZrO2 (FSZ) composite powders were synthesized by a co-precipitation method and the corresponding soft magnetic composites (SMCs) were fabricated with the powder metallurgy technique. The FSZ powders fabricated with 80 mmol/L tetraethyl orthosilicate and 20–40 mmol/L ZrOCl2·8H2O exhibits a dense and uniform SiO2–ZrO2 insulating layer with high Si–O and Zr–O binding energies, high saturation magnetization (Ms > 200.4 emu/g), and low coercivity (Hci, < 45.9 Oe). Compared with Fe@SiO2 SMCs, Fe@SiO2–ZrO2 SMCs have a higher resistivity of 941.9–984.2 μΩ m, and most of the eddy current losses are suppressed, contributing to superior alternating current magnetic properties, including a flat frequency character up to 1 MHz, lower core loss (Ps) of 17.9–19.2 W/kg (20 mT/100 kHz) and high permeability (μm) of 64–73. Electron probe microanalysis measurements confirmed that Fe powders are fully separated by a thin insulating layer composed of a large amount of SiO2 and a small fraction of ZrO2, which displays outstanding pressure resistance and thermal stability characteristics and contributes to the fabrication of SMCs with high resistivity and low core loss.