Abstract: FeSiAl-based soft magnetic composites (SMCs), prepared from insulated FeSiAl powders, are widely applied in electronic devices. However, it is still challenging to achieve high magnetic and mechanical properties simultaneously due to the undesirable insulation layer. Here, double Al₂O₃ insulation layers are prepared for FeSiAl SMC. Atomic-scale characterizations reveal an in-situ epitaxial Al₂O₃ layer at FeSiAl surface under the catalysis of NaAlO₂, and an outer amorphous Al₂O₃ layer by subsequent NaAlO₂ hydrolysis. The above structure ensures effective insulation of FeSiAl powders and excellent magnetic properties of the FeSiAl/NaAlO₂ SMC, with permeability of 101 and power loss of 128 mW/cm³ (50 mT, 100 kHz) respectively. Moreover, in-situ Al₂O₃/amorphous Al₂O₃ on FeSiAl matrix also leads to distinguished crush strength of 36.5 MPa for the core sample, which is ascribed to the enhanced adhesion at different interfaces as evidenced by similar local oxygen coordination and low strain distribution. This work provides a novel method to fabricate high-performance FeSiAl SMCs.

Key words: Soft magnetic composites, Interfacial structure, In-situ Al₂O₃, Power loss, Crush strength