High-performance ultra-thin SiO2 layer encapsulated FeSiAl soft magnetic composites for low-loss 100 kHz- 4 MHz power applications

Soft magnetic composites (SMCs) play a crucial role in inductors for new energy vehicles, for which remains challenges in maintaining high permeability and reducing loss at kHz-MHz frequences. As an oxide with high resistivity of 10¹⁵–10¹⁶ Ω cm, SiO₂ is promising for high-frequency applications due to its disordered nano-skeleton structure and ultra-stability, whereas FeSiAl is advantageous with approaching zero magneto-crystalline anisotropy and magnetostriction. Here, thin SiO₂ layer is covered FeSiAl powders with silane coupling agent (KH550) and tetraethyl orthosilicate (TEOS) using the sol-gel method, in which the thickness of layer is designed by varying the concentration of TEOS. The influence of SiO₂ layer on microstructure and magnetic properties of SMCs have been investigated. A thin SiO₂ layer can achieve synchronous reduction of eddy current loss and hysteresis loss while maintaining high permeability through electrical/magnetic isolation of FeSiAl powders. FeSiAl powders are uniformly coated with a ∼10 nm SiO₂ layer, endowing SMCs a high crush strength of 162 N, cut-off frequency of 68.48 MHz, a large magnetic permeability of 96.6 (@ 1 MHz), low power of 65.4 kW/m³ (50 mT, 100 kHz) and 260.4 kW/m³ (5 mT, 4 MHz). The comprehensive soft magnetic properties of the prepared FeSiAl/SiO₂ SMCs are superior to those reported in literatures, which would be potentially applied to high-performance inductors in 100 kHz- 4 MHz frequency ranges.