Synthesis, oxidation resistance and microwave absorbing properties of FeCo-based heterostructures

Abstract The fabrication of a shell on the surfaces of ferromagnetic particles has been proved to be an efficient approach to tailoring and improving the electromicrowave (EM) absorption. In this study, core–shell composites (FeCo@SiO2/TiO2, FeCo@SiO2@TiO2) were designed and fabricated by facile hydrolysis reactions. In these novel composites, the combined effects of the characteristics of each component result in excellent properties. The FeCo core exhibits strong magnetic loss, and the SiO2/TiO2 shell not only acts as an impedance matching medium, but also exhibits excellent dielectric loss. Moreover, the SiO2 and TiO2 can efficiently limit direct contact between FeCo particles and protect the FeCo core from oxidation at high temperature. The FeCo@SiO2, FeCo@TiO2, and FeCo@SiO2@TiO2 absorbers exhibit enhanced EM absorption, with maximum reflection losses (RLmax) of −38.49, −36.53, and −33.72 dB at thicknesses d of 2, 5, and 3 mm, respectively, compared to −19.23 dB for FeCo single particles (d = 5 mm). The improvement is due mainly to the improved impedance matching and multiple interfacial polarization. In particular, after annealing at 500 °C, the RLmax values of the FeCo@SiO2, FeCo@TiO2, and FeCo@SiO2@TiO2 absorbers are −25.41, −24, and −32.38 dB at thicknesses of 3, 3, and 5 mm, respectively, which are much higher than that of uncoated FeCo (−1.39 dB, d = 5 mm). These findings demonstrate that the fabricated FeCo-based core–shell structures can be good candidates for use as room- and high-temperature EM absorbers.