Ferrero Rocher® chocolates-like FeCo/C microspheres with adjustable electromagnetic properties for effective microwave absorption

Magnetic-dielectric composites are widely used in microwave absorption applications and have been continuously concerned by researchers. The synthesis of high-performance microwave absorbers with specific structures is a hot research topic. However, the question on how to reasonably combine the magnetic and dielectric components for achieving excellent microwave absorption performance still remains unanswered. In this study, FeCo/C microspheres were synthesized by a two-step hydrothermal method. FeCo nanoparticles were embedded in carbon spheres and formed the graphite layers, which is similar to Ferrero Rocher® chocolates. The electromagnetic parameters can be effectively adjusted by controlling the hydrothermal reaction time and excellent microwave absorption properties can be achieved at a low filling ratio. The FeCo/C microspheres exhibit the maximum reflection loss of – 20.61 dB and – 51.36 dB at the thickness of 1.6 mm and 2.6 mm, respectively. The effective absorption bandwidth of these microspheres is about 4.3 GHz. The specific Ferrero Rocher® chocolates-like multi-level structure increases to a large extent the material's conduction loss and polarization relaxation loss. At the same time, the reasonable ratio of the magnetic and dielectric components significantly improves the impedance matching. Therefore, this study is aimed at providing insights into understanding of the absorption mechanism and reliable references to the design of magnetic-dielectric composed microwave absorbers.