A study of the magnetic and electromagnetic properties of γ-Fe2O3–multiwalled carbon nanotubes (MWCNT) and Fe/Fe3C–MWCNT composites

A ferromagnetic γ-Fe2O3–MWCNT composite was prepared by a reverse microemulsion technique, and was transformed to a Fe/Fe3C–MWCNT composite by further heat-treatment in H2 atmosphere at 950 °C. TEM result suggests that MWCNTs are both surface decorated and filled with γ-Fe2O3 or Fe/Fe3C nanoparticles. The saturation magnetization and anisotropy field are particularly strong for Fe/Fe3C–MWCNT. The reflection loss of Fe/Fe3C–MWCNT is better than that of γ-Fe2O3–MWCNT at all frequencies between 2 and 18 GHz, resulting from enhanced magnetic loss and better matched characteristic impedance, rather than electric loss, as shown by the complex relative permeability μr=μ′r−jμ″rμr=μ′r−jμ″r and permittivity εr=ε′r−jε″rεr=ε′r−jε″r. The microwave absorbing properties can be modulated simply by manipulating the thickness of the prepared Fe/Fe3C–MWCNT composite for application in different frequency bands.