Hollow CoFe2O4–Co3Fe7 microspheres applied in electromagnetic absorption.

In this work, monodisperse hollow cobalt ferrite (CoFe 2 O 4 ) 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 CoFe 2 O 4 –Co 3 Fe 7 microspheres. Scanning electron microscopy and transmission electron microscopy images showed that the CoFe 2 O 4 –Co 3 Fe 7 microspheres retained hollow structure. Microwave absorption results revealed that hollow CoFe 2 O 4 –Co 3 Fe 7 microspheres exhibited much stronger electromagnetic absorption than the original hollow CoFe 2 O 4 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 CoFe 2 O 4 –Co 3 Fe 7 microspheres could be used as a new candidate for microwave absorbents, especially in Ku-band. [ABSTRACT FROM AUTHOR]