Preparation of core-shell Zn-doped CoFe₂O₄ cubes @CNT composites and their absorbing performances

Core-shell structured composites of Zn-doped CoFe₂O₄ cubes @CNTs were in situ synthesised using a CVD method at 450°C with Zn-doped CoFe₂O₄ cubes as catalysts and ethanol as carbon source. The as-obtained products were characterised using an X-ray diffractometer, transmission electron microscope, thermogravimetric analyser and vibrating sample magnetometer. Results demonstrated that CNTs uniformly grew on the surface of Zn doped CoFe₂O₄ cubes to form the shell with average diameter of 20-80 nm. The average diameter of the core/shell Zn-doped CoFe₂O₄ @CNTs cubes range from 3 to 10 μm. The magnetic hysteresis curves of Zn-doped CoFe₂O₄ cubes @CNTs illustrated the strong magnetic response to a varying magnetic field and the saturation magnetisations for the composites obtained at 450 and 600°C were 33.55 and 10.05 emu g^-1, respectively. A minimum reflection loss of -9.98 dB was observed at 9.2 GHz for the Zn-doped CoFe₂O₄@CNTs core/shell composites with a thickness of 2 mm. The Zn-doped CoFe₂O₄@CNTs core/shell composites prepared at a higher temperature exhibited better microwave absorbing performance than the sample prepared at a lower temperature.