Synthesis and microwave absorbing properties of Ni–Cu ferrite/MWCNTs composites

The electromagnetic and microwave absorbing properties of the nickel–copper (Ni–Cu) nanoferrites and multi-walled carbon nanotubes (MWCNTs) filled into epoxy resin were investigated in the X band (8.2–12.4 GHz), and the Ni–Cu nanoferrites were synthesized using auto-combustion method. The Ni–Cu ferrite annealing temperature was chosen at 600 °C to obtain the good magnetic properties. When the MWCNTs were added, the values of complex permittivity were enhanced by improving the interfacial polarization. The magnetic properties may be attributed to increase the concentration of Fe³⁺ ions in octahedral sites, which in turn induces the magnetization of the Ni–Cu ferrite. By changing the MWCNTs content, the optimizing reflection loss bandwidth below −10 dB can reach 3.2 GHz with the absorber thickness of 2.3 mm.