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The porous Fe 3 O 4 /carbon core/shell nanorods were fabricated via a three-step process. R-Fe 2 O 3 nanorods were first obtained, and R-Fe 2 O 3 /carbon core/shell nanorods were subsequently fabricated using glucose as a carbon source by a hydrothermal method, in which the thickness of the carbon coating was about 3.5 nm. Fe 3 O 4 /carbon core/shell nanorods were synthesized after an annealing treatment of the product above under a mixture of Ar/H 2 flow. After the H 2 deoxidation process, the Fe 3 O 4 core exhibited a character of porosity; the thickness of the carbon shell was decreased to about 2.5 nm, and its degree of graphitization was enhanced. The interesting core/ shell nanostructures are ferromagnetic at room temperature, and the Verwey temperature was about 120 K. Electromagnetic properties of the core/shell nanorodÀwax composite were investigated in detail. The maximum reflection loss was about À27.9 dB at 14.96 GHz for the composite with a thickness of 2.0 mm, and the absorption bandwidth with the reflection loss below À18 dB was up to 10.5 GHz for the absorber with the thickness of 2À5 mm. The excellent electromagnetic wave absorption properties of the porous Fe 3 O 4 /carbon core/shell nanorods were attributed to effective complementarities between the dielectric loss and the magnetic loss.

Porous Fe3O4/SnO2 core/shell nanorods are successfully fabricated, in which the width and the length of the pores are 5−10 and 10−60 nm, respectively. We prepared 80 wt % of porous Fe3O4/SnO2 core/shell nanorod-wax composites in order to measure their electromagnetic parameters. The measured results indicate that effective complementarities between the dielectric loss and the magnetic loss are realized over 2−18 GHz frequency range, suggesting the porous Fe3O4/SnO2 core/shell nanorods have excellent electromagnetic wave absorption properties. The reflection loss was calculated in terms of the transmit-line theory. The absorption range under −20 dB is from 3.2 to 16.88 GHz for an absorber thickness of 2−5 mm. Moreover, the porous core/shell nanorods exhibit dual-frequency absorption characteristics and their maximum reflection loss reaches −27.38 dB at 16.72 GHz as the absorber thickness is 4 mm. The excellent microwave absorption properties of the porous Fe3O4/SnO2 core/shell nanorods are attributed to effective complementarities between the dielectric loss and the magnetic loss and the special core−shell structures.

This paper presents for the first time a successful synthesis of quaternary nanocomposites consisting of graphene, Fe(3)O(4)@Fe core/shell nanopariticles, and ZnO nanoparticles. Transmission electron microscopy measurements show that the diameter of the Fe(3)O(4)@Fe core/shell nanoparitcles is about 18 nm, the Fe(3)O(4) shell's thickness is about 5 nm, and the diameter of ZnO nanoparticles is in range of 2-10 nm. The measured electromagnetic parameters show that the absorption bandwidth with reflection loss less than -20 dB is up to 7.3 GHz, and in the band range more than 99% of electromagnetic wave energy is attenuated. Moreover, the addition amount of the nanocomposites in the matrix is only 20 wt %. Therefore, the excellent electromagnetic absorption properties with lightweight and wide absorption frequency band are realized by the nanocomposites.