Collaborative tailoring of impedance/attenuation of flaky FeSiAl particles via vacuum annealing

The development of advanced electromagnetic wave absorbing materials is of great significance, yet existing absorbers often fail to achieve both good impedance matching and strong attenuation simultaneously. In this work, a simple one-step vacuum annealing process is employed to form an in-situ multilayer oxide structure on the surface of flaky FeSiAl particles. This multi-layer structure consists of alternating Fe₃O₄ and Al₂O₃/SiO₂ oxide layers, introducing numerous heterogeneous interfaces between the FeSiAl matrix and the layers, as well as across interlayer boundaries, generating strong interfacial polarization. Meanwhile, the high-resistivity oxide layers (e.g., Al₂O₃ and SiO₂) effectively suppress eddy current losses, while the FeSiAl matrix retains most of its iron from consumption, allowing the substrate to maintain its magnetic loss capability. More importantly, by adjusting the thickness and dielectric response of the multi-layer structure, the complex permittivity can be flexibly modulated, leading to a significantly improved impedance matching. Consequently, the coating filled with the properly treated FeSiAl particles was predicted to possess a minimum reflection loss of –63.6 dB at 1.19 GHz. At a coating thickness of 2.0 mm, the width of the band within which the reflection loss is less than –5 dB (EAB₅) reaches 7.94 GHz (1.80–9.74 GHz), covering the L-S band. At 5.0 mm thickness, the EAB₅ attains 6.37 GHz (0.63–7.00 GHz), nearly covering the P-L band. This work highlights the potential of in-situ interface engineering as a promising strategy for enhancing FeSiAl materials, providing a foundation for further optimization of electromagnetic properties and achieving highly efficient electromagnetic wave absorption in the P band.