Synthesis, multi-nonlinear dielectric resonance, and excellent electromagnetic absorption characteristics of Fe₃O₄/ZnO core/shell nanorods

Fe₃O₄/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 Fe₃O₄ and ZnO, and electron transfer between Fe²⁺ and Fe³⁺ ions in Fe₃O₄. 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 Fe₃O₄/ZnO core/shell nanorods are attractive candidates for a new kind of the electromagnetic wave absorptive materials.