Full X-Ku band microwave absorption by Fe(Mn)/Mn7C3/C core/shell/shell structured nanocapsules

New type of Fe(Mn)/Mn₇C₃/graphite nanocapsules was prepared by a modified arc discharge technique in ethanol vapor, with Fe(Mn) solid solution nanoparticles as the core, Mn₇C₃ as the inner shell, and graphite as the outer shell. The Cole-Cole semicircle approach was adopted to explain the ternary dielectric resonance, due to a cooperative consequence of the core/shell/shell interfaces and the dielectric Mn₇C₃ and C shells. A remarkable increase in the anisotropy energy led to a shift in the natural resonance frequency to 6.6 GHz. Dielectric losses come from the ternary dielectric resonance while magnetic losses were from the magnetic natural resonance. An optimal reflection loss (RL) of −142.1 dB was observed at 12 GHz for 5.0 mm thickness layer. RL exceeding −10 dB was obtained at 6.6-18 GHz for 1.4 mm thickness, covering the whole X band (8-12 GHz), Ku band (12-18 GHz), and some of C band (6.6-8.0 GHz). RL exceeding −20 dB was found at 6-10.6 GHz for 2.2 mm thickness.