Decoration of nanocarbon solids with magnetite nanoparticles: towards microwave metamaterial absorbers
Three methods for decoration of nanocarbon solids (NcSs) with magnetite nanoparticles (MaNPs) were compared, namely covalent linkage, direct co-precipitation and solvothermal synthesis. The influence of each method on the obtained nanocomposites' most relevant characteristics was studied, such as chemical identity, size, loading rate and spatial distribution of the MaNPs over the NcS. The impact of the variables controlling the solvothermal decoration of a wide variety of NcSs was investigated in more detail, such as the nature of the iron precursor and the NcS (type and oxidation state), the reaction temperature, time and water content. Finally, the obtained nanocomposites' superparamagnetic MaNPs were found to induce a ferromagnetic resonance (FMR) phenomenon, imparting a natural or zero-field resonance around 4 GHz. It was also demonstrated that the amount of loaded MaNPs had an effect on the FMR absorption intensity as well as on the nanocomposites' electrical properties. The latter were also shown to be governed by the chosen NcS type. These features could easily be exploited as control mechanisms to construct highly effective microwave metamaterial absorbers possessing low incident microwave reflection and maximal absorption rates.