▎ 摘　　要

In this study, nitrogen (N)-doped graphene-coated FeNi nanoparticles were fabricated onto N-doped carbon (NC) nanosheets (FeNi@NGLs/NC) by a simple method. The simulations based on the Havriliak-Negami (H-N) model show two relaxation peaks resulting from the dipole and interfacial polarizations in the dielectric spectra of FeNi@NGLs/NC, Ni@NGLs/NC, and Fe3C/Fe@NGLs/NC. Among these samples, Ni@NGLs/NC exhibits the largest dielectric loss, which is related to its high conduction loss below 8 GHz and relaxation loss over the range 2-18 GHz. Through simulations based on the Gilbert modification of the Landau-Lifshitz equation, different numbers of resonance peaks are derived from the permeability-frequency plots of these samples. Further theoretical calculations indicate that the number and position of these resonance peaks are dependent on the type of metal nanoparticles (NPs) in the samples. Despite having the largest dielectric loss, Ni@NGLs/NC exhibits the worst electromagnetic wave (EMW) absorption properties among the three samples, because of its poor impedance matching characteristics, caused by the skin effect. These results not only uncover the origin of dielectric and magnetic losses in magnetic carbon composites, but also demonstrate the importance of the balance between the loss and impedance matching for an EMW absorber. (C) 2020 Elsevier B.V. All rights reserved.