Hollow CoFe2O4-Co3Fe7 microspheres applied in electromagnetic absorption

In this work, monodisperse hollow cobalt ferrite (CoFe2O4) microspheres with mean diameter of 150 nm and shell thickness of 50 nm have been successfully prepared via a one-pot solvothermal method. In order to improve the microwave absorption, a thermal reduction process was designed to synthesize hollow CoFe2O4-Co3Fe7 microspheres. Scanning electron microscopy and transmission electron microscopy images showed that the CoFe2O4-Co3Fe7 microspheres retained hollow structure. Microwave absorption results revealed that hollow CoFe2O4-Co3Fe7 microspheres exhibited much stronger electromagnetic absorption than the original hollow CoFe2O4 microspheres. Most importantly, when the sample thickness was 1.3 mm, the reflection loss (RL) less than -10 dB was obtained in the frequency range of 12.5-17.7 GHz, which nearly covered the entire Ku-band. When the sample thickness increased to 2 mm, the minimum RL was as high as -41.6 dB with the effective bandwidth (the bandwidth of RL at -10 dB) of 3 GHz. The enhanced microwave absorption was attributed to efficient complement between dielectric loss and magnetic loss. These results indicated that the hollow CoFe2O4-Co3Fe7 microspheres could be used as a new candidate for microwave absorbents, especially in Ku-band. (C) 2014 Elsevier B.V. All rights reserved.