Microwave electromagnetic properties of multiwalled carbon nanotubes filled with Co nanoparticles

Multiwalled carbon nanotubes filled with face centered cubic Co nanoparticles (MWCNTs/Co) were successfully prepared by a chemical reducing method. The average outer diameter of MWCNTs is about 40 nm and the size of Co nanoparticles is in the range from 5 to 20 nm. The relative permeability and permittivity spectra of MWCNTs/Co resin composites with 50 wt % powders were measured in the frequency range of 0.1–18 GHz. Three resonance absorption peaks are observed in the μ″−f spectrum: the peak around 5.0 GHz can be attributed to natural resonance, while the other two appear around 10.6 and 16.9 GHz are induced by exchange resonance. It is found that the peak with minimum reflection loss (RL) value moves to lower frequencies and the RL value increases from 4.2 to 10.1 dB with the increase of the absorber’s thickness from 2 to 6 mm.