Since electromagnetic pollution is becoming more and more serious, novel composite microwave absorbents are gaining much attention. Here, Co3Fe7/C core shell microspheres for microwave absorption were synthesized for the first time. At first, hollow CoFe2O4 microspheres were prepared via a solvothermal method at 200 degrees C for 15 h. Then CoFe2O4-hydrochar microspheres were synthesized by hydrothermal method in an aqueous glucose solution containing hollow CoFe2O4 microspheres. After annealed under Ar atmosphere at 500 degrees C, the CoFe2O4-hydrochar microspheres were converted into CoFe204 Co3Fe7/C microspheres. Co3Fe7/C core shell microspheres came into being after annealed at 600 degrees C. Both the CoFe204 Co3Fe7 nanoparticles and Co3Fe7 nanoparticles were encapsulated in the carbon shells, and the microsphere morphology could be retained during the carbothermal process. Especially, the core shell structure caused that the density of the Co3Fe7/C microspheres was below 2 g/cm(3). Resulting from the synergistic effect of Co3Fe7 nanoparticles and partially graphitized carbon, the minimum reflection loss (RL) of Co3Fe7/C microspheres was as low as 44.4 dB obtained with 1.6 mm thickness. Owing to the characteristics of low density and good microwave absorption, the Co3Fe7/C core shell microspheres could be used as a lightweight and highly efficient microwave absorbent. (C) 2015 Elsevier B.V. All rights reserved.