High-Performance FeSiAl Soft Magnetic Composites with Hybrid Insulating Layers of Fe₃O₄/Al₂O₃/SiO₂ Prepared Via In Situ Oxidation

Soft magnetic composites (SMCs) are key electromagnetic conversion materials for kHz-MHz electronic devices. Traditional SMCs introduce foreign insulation materials to reduce eddy current loss, resulting in an imbalance among effective permeability (μ_e), core loss (P_cv), and direct current (DC) bias. In this work, FeSiAl composites are oxidized in air, which enables the in situ generation of a thin and dense Fe₃O₄/Al₂O₃/SiO₂ hybrid insulating layer on the surface of FeSiAl. The hybrid oxide layer effectively reduces power loss and provides frequency stability and thermal stability of permeability. The ferromagnetic Fe₃O₄ alleviates magnetic dilution and ensures high permeability. For powder oxidized for 60 min at 600°C, the core has low P_cv of 55.3 mW/cm³ (50 mT/100 kHz) and 329 mW/cm³ (100 mT, 100 kHz), stable μ_e of 46.5 up to 140°C, and high DC bias of 56.8% at 100 Oe. For powder oxidized for 90 min at 600°C, P_cv of 436.2 mW/cm³ (5 mT/7 MHz) and a cutoff frequency of 267.6 MHz are obtained. This study offers a facile strategy for preparing high-performance SMCs for high-frequency electronic devices.