Abstract: CoxFe3-xO4 (0≤x≤1) spheres, a mixture of Fe3O4 and CoFe2O4, were synthesized via solvothermal reaction by changing the Co to Fe ratio in ethylene glycol solution.For the solution containing ingredients (atom ratio of Co∶Fe=1∶1,1∶2,1∶4 and 0), the obtained spheres are CoFe2O4, Co0.9Fe2.1O4, Co0.73Fe2.27O4 and Fe3O4 at 200 ℃, respectively.The calculated reflectivity indicates that for the composite containing magnetite(75wt;) and parraffin wax, the lowest reflection loss is-38 dB at 4 GHz with 5.5 mm thickness.The composite containing Co0.9Fe2.1O4 spheres displays better microwave absorption capability.The minimum reflection loss reaches-41.1 dB at 12.08 GHz and the matching thickness is 2 mm.Dielectric loss contributes even more than magnetic loss in the frequency range of 3-14 GHz.The work proves that variation of cobalt element in spheres can change the proportion of CoFe2O4 to Fe3O4, the resonance frequency together with the crystallinity of the spheres, and ultimately the dielectric character and the microwave absorption property.

Key words: CoxFe3-xO4 (0≤x≤1) spheres, a mixture of Fe3O4 and CoFe2O4, were synthesized via solvothermal reaction by changing the Co to Fe ratio in ethylene glycol solution.For the solution containing ingredients (atom ratio of Co∶Fe=1∶1,1∶2,1∶4 and 0), the obtained spheres are CoFe2O4, Co0.9Fe2.1O4, Co0.73Fe2.27O4 and Fe3O4 at 200 ℃, respectively.The calculated reflectivity indicates that for the composite containing magnetite(75wt;) and parraffin wax, the lowest reflection loss is-38 dB at 4 GHz with 5.5 mm thickness.The composite containing Co0.9Fe2.1O4 spheres displays better microwave absorption capability.The minimum reflection loss reaches-41.1 dB at 12.08 GHz and the matching thickness is 2 mm.Dielectric loss contributes even more than magnetic loss in the frequency range of 3-14 GHz.The work proves that variation of cobalt element in spheres can change the proportion of CoFe2O4 to Fe3O4, the resonance frequency together with the crystallinity of the spheres, and ultimately the dielectric character and the microwave absorption property.