Reaction-mediated interfacial design with Sputtering-based Bi2O3 coating onto powder surface for low-loss, high-permeability Fe-Si soft magnetic composites

초록

Soft magnetic composites require a delicate balance between interparticle electrical insulation and magnetic coupling to achieve both low core loss and high magnetic performance simultaneously. Here, we demonstrate a reaction-mediated interfacial design strategy for soft magnetic composites induced by nanoscale Bi2O3 coatings using sputtering-based powder coating. Conformal Bi2O3 layer with control over the thicknesses in the range of 10–80 nm were deposited on spherical Fe-Si powders with negligible magnetic dilution. After compaction and subsequent annealing over the temperature range in 200–800 ℃, the Bi2O3-derived interphase evolved through temperature-dependent solid-state reactions, producing a stratified oxide architecture consisting of BiFeO3 and Fe3O4 with a SiO2-rich barrier near the Fe-Si surface at 600 ℃. The optimized sample, featuring a 40 nm-thick Bi2O3 layer annealed at 600 ℃, exhibits the highest electrical resistivity along with significantly improved magnetic properties including reduced coercivity and enhanced permeability resulting in a reduced Pcv of 272.9 mW/cm3 at 50 mT and 100 kHz. This work highlights sputtering-based powder coating as a scalable route to precisely tailor the interface of soft magnetic materials for high-performance magnetic components. © 2026 The Authors

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