Fabrication of core–shell nickel ferrite@polypyrrole composite for broadband and efficient electromagnetic wave absorption

• Nickel ferrite@polypyrrole (NiFe 2 O 4 @PPy) composite was prepared by a two-step way. • The obtained NiFe 2 O 4 @PPy magnetic composite showed a unique core–shell structure. • Minimum reflection loss of −56.25 dB was reached at a filling ratio of 17.5 wt%. • Maximum effective absorption bandwidth was 7.12 GHz, covering the whole Ku-band. • RCS contribution of NiFe 2 O 4 @PPy composite in the far-field was simulated by CST. Herein, nickel ferrite@polypyrrole (NiFe 2 O 4 @PPy) composite was prepared by a simple two-step route of solvothermal synthesis and in-situ oxidation polymerization reaction. The results of micromorphology analysis showed that the obtained NiFe 2 O 4 @PPy composite had a unique core–shell structure, good magnetic performance and electrical conductivity. Furthermore, the as-prepared magnetic/conductive NiFe 2 O 4 @PPy composite exhibited notably enhanced electromagnetic wave (EMW) absorption performance than pure NiFe 2 O 4 and PPy. When the filling ratio was 17.5 wt% and the matching thickness was 2.24 mm, the optimal minimum reflection loss ( RL min ) of −56.25 dB and a broad effective absorption bandwidth (EAB) of 5.2 GHz were achieved for NiFe 2 O 4 @PPy composite. With slightly increasing the matching thickness to 2.6 mm, the maximum EAB of 7.12 GHz could be reached. Additionally, the probable EMW absorption mechanism was elucidated. Therefore, this work could provide a valuable reference for the preparation of magnetic ferrite/conductive polymer composites as broadband and high-efficiency EMW absorbers.