Synergistic fabrication of FeSiAl/Si3N4 soft magnetic composites by two-step plasma-assisted ball milling and magnetic-field-induced orientation

To overcome the rapid permeability degradation, high eddy-current loss, and poor thermal management of FeSiAl soft magnetic composites under high-frequency and high-power conditions, a combined strategy of two-step plasma-assisted ball milling and magnetic-field-induced orientation was developed. The first plasma-assisted milling step transformed near-spherical FeSiAl powders into high-quality flakes, while the second step constructed a dense Si 3 N 4 coating layer, forming a tightly bonded core–shell structure. Interfacial analyses revealed the formation of Si–N, Si–O–N, and Fe–N/Al–N bonds. First-principles calculations further demonstrated interfacial charge transfer from FeSiAl to Si 3 N 4 , leading to strong Al–N covalent bonding, a built-in electric field, and a Schottky barrier, which effectively suppressed interparticle charge transport and reduced high-frequency eddy-current loss. Meanwhile, magnetic-field-induced orientation promoted the ordered arrangement of flaky particles, improving magnetic-flux continuity and heat-transfer pathways. The optimized composite containing 4 wt% Si 3 N 4 achieved an effective permeability of 93.4 at 1 MHz, a total core loss of 72.2 kW/m 3 at 50 mT and 100 kHz, and a thermal conductivity of 25.9 W·m −1 ·K −1 . This work provides a new route for designing soft magnetic composites for high-frequency, high-power-density power electronic devices.