The enhanced microwave absorption property of CoFe2O4 nanoparticles coated with a Co3Fe7-Co nanoshell by thermal reduction

CoFe2O4 nanoparticles were fabricated by a sol-gel method and then were coated with Co3Fe7-Co by means of a simple reduction process at different temperatures under 2% H-2 with the protection of argon to generate the dielectric-core/metallic-shell structure. The optimum reflection loss (RL) calculated from permittivity and permeability of the 80 wt% CoFe2O4/Co3Fe7-Co and 20 wt% epoxy resin composites reached -34.4 dB, which was much lower than that of unreduced CoFe2O4 and epoxy resin composites, at 2.4 GHz with a matching thickness of 4.0 mm. Moreover the RL exceeding -10 dB in the maximum frequency range of 2.2-16 GHz was achieved for a thickness of composites of 1.0-4.5 mm with 600 degrees C thermal reduction process. The improved microwave absorption properties are a consequence of a proper electromagnetic match and the enhanced magnetic loss besides its dielectric loss due to the existence of the core/shell structure in CoFe2O4 composites. Thus, the reductive CoFe2O4 nanoparticles have great potential for being a highly efficient microwave absorber.