Fig. 1. SEM images of C/Co-500（a），C/Co-550（b）and C/Co-600（c）. EDS（d），TEM images（e，f）and HRTEM（g）of C/Co-550

Fig. 2. XPS spectra of（a）survey spectrum，（b）C 1s，（c）Co 2p，（d）N 1s，（e）Raman and（f）Magnetic hysteresis loops of C/Co-500，C/Co-550 and C/Co-600

Fig. 3. Complex permittivity（a）and complex permeability，（b）of C/Co-500，C/Co-550 and C/Co-600 composites with 35 wt% filling concentration，（c）dielectric loss tangent，（d）magnetic loss tangent of C/Co-500，C/Co-550 and C/Co-600 composites

Fig. 4. Cole-Cole circles（a）and C₀ curves，（b）of C/Co-500，C/Co-550 and C/Co-600

Fig. 5. RL curves of C/Co-500（a），C/Co-550（b）and C/Co-600（c），（d）t_m curve，（e）three-dimensional representations and（f）two-dimensional color contour RL values of C/Co-550

Fig. 6. Structure of one unit（a）top view，（b）cross section view，（c）periodic unit structures，（d）Reflection loss of single layer and all-dielectric metamaterial of C/Co-500 composite，（e）Reflection loss of C/Co-500 all-dielectric metamaterial absorbers under 2~22 GHz

Fig. 7. The distributions of magnetic field density，electric field density and power loss density under normal incidence at 8.6 GHz（a，b，c），11.4 GHz（d，e，f）and 19.5 GHz（g，h，i）