Magnetic negative permittivity with dielectric resonance in random Fe3O4@graphene-phenolic resin composites

Magnetic Fe3O4@graphene-phenolic resin (FGR-PR) composites with negative permittivity were prepared by chemical coprecipitation and pressing method. Alternating current conductivity, permittivity, and permeability of the FGR-PR composites were investigated. An obvious percolation phenomenon was observed with the increase of FGR content from 84 to 91 vol%. Two types of negative permittivity attributed to the Lorentz and the Drude model, respectively, were observed in the composites. Due to the magnetocrystalline anisotropy and saturation magnetization, the real permeability enhanced from 1.17 to 4.1 with the increasing FGR content from 6 to 98 vol%. In addition, the frequency dispersion of permeability was attributed to the domain wall and the gyromagnetic spin resonance. The magnetic loss decreased firstly in the low frequency, attributing to the natural resonance, and then increased in the high frequency from the eddy current.