Preparation, characterization and microwave absorption properties of NiFe2O4 and its composites with conductive polymer

Abstract

Spinel ferrite NiFe2O4 was synthesized by polyacrylamide sol–gel method, and its composites with polyaniline (PANI) and polypyrrole (PPY) were prepared via in situ emulsion polymerization. The morphology of NiFe2O4 had a flake structure, while that of NiFe2O4/PANI and NiFe2O4/PPY composites existed a flake-grain structure. The magnetic properties (Ms, Mr and Hc) of NiFe2O4/PPY were lower than those of NiFe2O4/PANI, and they were all lower than those of NiFe2O4. NiFe2O4/PPY composite exhibited a higher conductivity value of 3.76 S/cm than that of NiFe2O4 and NiFe2O4/PANI. Moreover, the imaginary part of permittivity also enhanced with the increase of conductivity, contributing to the increase of dielectric loss. The electromagnetic characteristics of NiFe2O4, NiFe2O4/PANI and NiFe2O4/PPY were also investigated with a vector network analyzer in 1–18 GHz. The absorbing peak position moved to lower frequency with the increasing thickness of NiFe2O4/PANI or NiFe2O4/PPY composites. Under the same condition, the minimum reflection loss of NiFe2O4/PPY was much lower than that of NiFe2O4 and NiFe2O4/PANI, indicating the incorporation between NiFe2O4 and PPY could reach a better matching in terms of electromagnetic parameters. The value of the minimum reflection loss was −42 dB at 8 GHz for NiFe2O4/PPY with a thickness of 3.5 mm, and a broad peak with a bandwidth lower than −10 dB was about 4.5 GHz.