Ultrahigh Fe₃O₄ Magnetic CrystalsLoading onto Crumpled Spherical Reduced Graphene Oxide for SuperbElectromagnetic Absorption in the C and X Frequency Bands

Poor microwave-absorbing performance of a carbonaceous–magnetic hybrid at low frequency is one of the great challenges that needs to be solved urgently. Constructing a three-dimensional structure of a graphene-based absorber with high-loading ferrite nanoparticles onto graphene surfaces is an effective strategy to boost the low-frequency absorbability. Therefore, we constructed substrates of crumpled monolayer graphene oxide spheres by first spray-drying and synthesized high-loading iron hydroxide nanograins onto the substrates by a simple oil-bath heating. Followed by an annealing treatment under Ar gas, an ultrahigh Fe₃O₄ magnetic crystals loading onto crumpled spherical reduced graphene oxide hybrid (Fe₃O₄@crGO) was obtained. The wrinkled architecture provides a large number of interface angles for ultrahigh Fe₃O₄ nanocrystals to avoid the massive agglomeration, which lowers the complex permittivity and improves the complex permeability to perfect absorber’s impedance matching at low frequency. Meanwhile, the impressive conducting loss of rGO, magnetic loss of Fe₃O₄ nanograins, polarization loss of heterogeneous interfaces, and multiple reflection and scattering of microwaves within the three-dimensional architecture boost the attenuation capability of the absorber. As a result, the as-prepared Fe₃O₄@crGO-30 hybrid exhibits a superb reflection loss of −52.3 dB at 5.4 GHz. In addition, by tailoring the thickness ranging from 2.5 to 5.0 mm, full coverage absorption in C and X bands can be achieved. This work provides a simple, efficient, and promising way to prepare a graphene-based absorber with perfect low- and middle-frequency absorption capacity.