Preparation of FeSiAl soft magnetic composites for MHz applications via rapid-thermal-processing technique

Soft magnetic composites (SMCs) with high saturation magnetic induction (B_s) and low power loss are expected to meet the demand for miniaturization and integration of high-frequency power devices. Although the insulating layer in SMCs reduces eddy current loss, it produces a magnetic dilution effect that reduces B_s, and produces a demagnetizing field that increases hysteresis loss. In-situ oxidation technology is an effective strategy to solve this structural contradiction. In this study, to synergistically control atomic diffusion of the matrix and interfacial chemical reactions at high temperatures, rapid-thermal-processing (RTP) technique is introduced to construct ultrathin insulating layer on the surface of FeSiAl. When RTP treated at 1000 ℃ for 5 seconds, Al₂O₃-rich composite insulating layer of about 15 nm is produced. The high resistivity insulation reduces eddy current loss, while high-temperature process significantly reduces the hysteresis loss, giving the SMCs a core loss of 946.4 mW/cm³ (15 mT, 3 MHz). Notably, after RTP treatment, the cut-off frequency of the sample elevates to 270 MHz, while M_s increases by 3.7 %. These outstanding properties show that the RTP technique is promising for the preparation of SMCs with high M_s, high cut-off frequency, and low core loss for applications in the MHz band.