Facile design of a ZnO nanorod-Ni core-shell composite with dual peaks to tune its microwave absorption properties

In this study, we report a facile one-pot hydrothermal way to prepare magnetic-dielectric Ni/ZnO composites. The effects of different solvents on the sizes and morphologies were investigated. The as-synthesized composites were characterized by X-ray diffraction, scanning electron microscopy, vibrating sample magnetometry, transmission electron microscopy (TEM), and vector network analyses. The results showed that the viscosity of the solvents plays an important role in determining the sizes and morphologies of the Ni/ZnO products. All of the three Ni/ZnO products possessed two wide attractive absorption bands, which could broaden the effective absorption bandwidth. The absorption peaks located at a relatively high frequency were related to strong dielectric resonances, which could induce a high eddy current effect, therefore prompting microwave absorption. Among the three Ni/ZnO composites, the core-shell Ni@ZnO prepared in ethylene glycol solution exhibited the best microwave absorption properties. The optimal reflection loss was -30.2 dB and the effective bandwidth (RL below -10 dB, meaning 90% microwave absorption) could be adjusted in the frequency range of 9.6-14.3 GHz with a low thickness of 1.7-2.5 mm. The outstanding absorption was attributed to suitable impedance matching, an antenna receiver mechanism and a point charge effect, and the interfacial polarization. This study reports a simple method to design a magnetic metal-dielectric semiconductor absorber.