Broadband and multilayer core-shell FeCo@C@mSiO₂ nanoparticles for microwave absorption

The core-shell composite of FeCo alloy coated with amorphous carbon and mesoporous silica (mSiO₂ for short) has been successfully fabricated through liquid-phase reduction, hydrothermal reaction as well as high temperature calcination, forming nanoparticles around 400 nm in size. The alloy core provides strong magnetic loss and keeps stable under the protection of the shell, while the carbon shell reduces density and promotes dielectric loss. The outer layer of mSiO₂ provides a larger specific surface area for multiple reflections, and meanwhile effectively adjusting the impedance matching, resulting in a better absorption. With a thickness of 3.5 mm, the maximum R_L of the composite reaches −46.79 dB at 11.84 GHz, and the effective absorption bandwidth with the R_L below −10 dB is up to 8.8 GHz (from 9.2 to 18.0 GHz). Hence, FeCo@C@mSiO₂ composite is potential to become an excellent candidate in the field of microwave absorption.