Influence of a graphite shell on the thermal, magnetic and electromagnetic characteristics of Fe nanoparticles

Graphite-coated Fe nanocapsules were prepared by arc discharge method. Fe nanocapsules have a core/shell microstructure, in which Fe nanoparticles as cores and graphite layers as shells. Compared with Fe nanoparticles with an oxide shell, the graphite shell can restrain the growth of Fe nanoparticles, which leads to lower saturation magnetization and higher natural resonance frequency. The Fe nanocapsules are stable securely below 220 °C in the air, due to the enhancement of thermal stability and the anti-oxidation by graphite layer shell. Dielectric relaxation of graphite shell and the interfacial relaxation between graphite shell and Fe core lead to the dual nonlinear dielectric resonance. Graphite shells can dramatically improve the magnetic/dielectric loss and the attenuation constant in the 2–18 GHz though the dual dielectric resonance and protection of Fe cores, leading to enhanced microwave absorption properties of Fe nanocapsules at 2–18 GHz.

► The graphite shell can lead to high natural resonance frequency.
► The Fe nanocapsules are stable securely below 220 °C in the air.
► Graphite shells improve the magnetic/dielectric loss and the attenuation constant.
► Dual resonance and protection of cores enhance microwave absorption properties.