Beyond the magnetic paradigm: Unveiling the dominant role of electron injection and heterointerface polarization for CoNi@C with enhanced microwave absorption

Developing microwave absorbing materials that integrate a wide effective absorption bandwidth (EAB) with superior angular and polarization stability is a key research direction in the field. In particular, MOF derived magnetic metal/carbon composites (MMOF-MM/C) that integrate both magnetic and electric loss mechanisms, have attracted widespread attention. To date, the role of the high content of magnetic metal in MMOF-MM/C for microwave absorption awaits systematic investigation. In this work, a microwave-assisted fast calcination strategy was proposed to synthesize well-dispersed, welded, homogenous CoNi@C-MW micro/nano hierarchical structure. Analysis of impedance matching ratios and attenuation constants reveals that the permeability of CoNi@C-MW contributes only minimally to microwave absorption in the 2.0–18.0 GHz frequency range. GA|NLLS fitting shows that CoNi metal enhances conduction and polarization losses in CoNi@C-MW, increasing polarization loss by nearly 50 % and conduction loss by up to three times. This is attributed to thicker, more graphitized carbon layers that facilitate electron injection from CoNi to carbon, and a well-dispersed, uniform particle structure that promotes heterogeneous interface polarization. Furthermore, a magnetic-dielectric-magnetic (M 1 –D–M 2 ) sandwich-structured absorber was further constructed, delivering an EAB covering 7.7–18.0 GHz at an angular stability up to 60° under both TE and TM polarizations.