Preparation of CoFe2O4/CoFe Particles with Broadband Microwave Absorption by Hydrogen Reduction

In this work, CoFe2O4/CoFe particles were prepared by two steps methods of ethylene glycol solvothermal and hydrogen reduction. The structure and morphology of the samples were characterized by X-ray diffraction and field-emission scanning electron microscopy. The samples were mixed with paraffin wax at a mass ratio of 3:1 to prepare rings with an inner diameter of 3.04 mm and an outer of 7 mm, and its electromagnetic parameters were measured by a network vector analyzer. The results show that the dielectric loss and magnetic loss of the composites can be improved after high temperature hydrogen reduction. The optimal reflection loss of −52.14 dB can be achieved at 12.34 GHz in a thickness of only 1.7 mm, when CoFe2O4 was annealed at 500°C for three hours, and the obtained particles can reach less than −20 dB in all C, X, and Ku bands. In all the samples annealing under 500–700°C, the maximum absorption bandwidth over 5.0 GHz can be observed. By comparing the impedance matching properties of CoFe2O4 precursor and CoFe2O4/CoFe composites, it is found that the tunability of the electromagnetic property in composite structure contributes to the excellent electromagnetic wave absorbing performances.