Fe 3 O 4 /TiO 2 core/shell nanotubes are fabricated via a three-step process. R-Fe 2 O 3 nanotubes are first obtained, and R-Fe 2 O 3 /TiO 2 core/shell nanotubes are subsequently fabricated using Ti(SO 4 ) 2 as a Ti source by a wet chemical process. The thickness of the amorphous TiO 2 shell is about 21 nm. After a H 2 deoxidation process, the amorphous TiO 2 layer changes into crystalline structures composed of TiO 2 nanoparticles with an average diameter of 2.5 nm, and its thickness is decreased to about 18 nm. At the same time, R-Fe 2 O 3 transforms into cubic Fe 3 O 4 . Consequently, crystalline Fe 3 O 4 /TiO 2 core/shell nanotubes can be fabricated through the process above. The measurements of the magnetic properties demonstrate that the Fe 3 O 4 /TiO 2 core/shell nanotubes exhibit ferromagnetic behavior at room temperature, and the Verwey temperature is about 120 K. The eddy current effect is largely reduced and the anisotropy energy is improved significantly for the core/shell nanotubes due to the presence of the TiO 2 shells. The maximum reflection loss reaches -20.6 dB at 17.28 GHz for the absorber with thickness of 5 mm, and the absorption bandwidth with the reflection loss below -10 dB is up to 13.12 GHz for the absorber with a thickness of 2-5 mm. Our results demonstrate that the Fe 3 O 4 /TiO 2 core/shell nanotubes obtained in this work are attractive candidate materials for the magnetic and EM wave absorption applications.

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.

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Fe 3 O 4 /ZnO core/shell nanorods are successfully fabricated by combing an inorganic-phase reaction with a hydrogen annealing process. The transmission electron microscopy analysis indicates that the diameter and the length of the core/shell nanorods are 25-80 and 0.35-1.2 µm, respectively. Electromagnetic properties of the core/shell nanorod-wax composites are investigated. The permittivity of the composites shows four dielectric resonant peaks in 2-18 GHz, which can be explained by the transmission line theory. The resonant behavior mainly results from interface polarization induced by the special core/shell structures, dipole polarization of both Fe 3 O 4 and ZnO, and electron transfer between Fe 2+ and Fe 3+ ions in Fe 3 O 4 . The maximum reflection loss is about -30 dB at 10.4 GHz for the composites with a thickness of 1.5 mm, and the absorption bandwidth with the reflection loss below -20 dB is up to 11 GHz for an absorber with the thickness in 2-4 mm. Thus, our results demonstrate that the Fe 3 O 4 /ZnO core/shell nanorods are attractive candidates for a new kind of the electromagnetic wave absorptive materials.