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NiFe 2 O 4 nanosheets have been synthesized via a simple surfactant-assisted solution route, which are confirmed by X-ray powder diffraction, scanning electron microscopy and transmission electron microscopy. The NiFe 2 O 4 sample exhibits the sheet-like structure, with width varying from 200 to 800 nm and thickness ranging from 20 to 60 nm. The electromagnetic properties of NiFe 2 O 4 nanosheetsparaffin composites have been deeply investigated. The multiple dielectric relaxation loss in NiFe 2 O 4 nanosheets is attributed to the size distribution and morphology of the NiFe 2 O 4 nanosheets. The magnetic loss in the present system is caused mainly by the natural resonance. An absorber with a thickness of 4.3 mm exhibits an optimal reflection loss (RL) value of -47.1 dB at 7.67 GHz. RL values exceeding -20 dB in the 2.68-17.96 GHz range are obtained by choosing an appropriate absorptionlayer thickness between 1.9 and 10 mm. Not only the RL peak frequency but also the number of the peaks can be well explained by the quarter-wavelength cancellation model.

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Ni@onion-like carbon (OLC)/reduced graphene oxide (RGO) nanocomposites were synthesized, and their multicomponent microstructure was confirmed by X-ray diffraction, transmission electron microscopy, Raman spectra, the thermal gravimetric analysis and magnetic hysteresis loops. The obtained nanocomposite possesses a unique structure, in which core–shell Ni@OLC nanocapsules are decorated on the surface of RGOs. The synergistic effect of the dielectric loss of RGO and OLC and the magnetic loss of Ni nanoparticles can be constructed. The RGO can provide tremendous electric dipoles. Multi-interface among RGO, OLC and Ni nanoparticles can enhance dielectric performance and cause multiple reflections. The combination of these merits makes the nanocomposite a promising candidate material for electromagnetic absorber. The 20[Formula: see text]wt.% nanocomposite-paraffin composite can possess an optimal reflection loss (RL) of [Formula: see text][Formula: see text]dB at 9.75[Formula: see text]GHz with a thickness of 3.1[Formula: see text]mm. When the thickness is 2.0[Formula: see text]mm, the RL of composite can reach [Formula: see text][Formula: see text]dB at 17.4[Formula: see text]GHz. The effective frequency is 6.54[Formula: see text]GHz (11.16–17.7[Formula: see text]GHz) for 2.4[Formula: see text]mm thickness layer.

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