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

► New type of Fe(Mn)/Mn7C3/graphite nanocapsules, with Fe(Mn) solid solution nanoparticles as the core, Mn7C3 as the inner shell, and graphite as the outer shell, is prepared by a modified arc discharge technique in ethanol vapor. ► The Cole-Cole semicircle approach is 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 leads to a shift in the natural resonance frequency to 6.6 GHz. ► BW−10 is 11.4 GHz (6.6-18 GHz) for 1.4 mm thickness layer, covering the whole X band, Ku band, and some of C band.