57Fe Mössbauer spectroscopy on multiwalled carbon nanotubes with metal filling

Mössbauer measurements at different temperatures are reported for MWCNTs with metallic encapsulations ("nanowires"). The spectra can reasonably be refined with two subpatterns: one providing clear evidence of an iron carbide Fe(3)C (cementite) phase as the main nanowire component and the other yielding a relaxation doublet most probably belonging to the same phase. Whereas the former one displays a well resolved magnetic hyperfine spectrum with Brillouin type temperature dependence, the latter one gains importance with rising temperature or onset of an inhomogeneous external magnetic field. The comparably large incoherent scattering is attributed to the graphene layers of the tube walls. The experimental results are discussed on the background of an interpretation model trying to explain unusual magnetometric results published elsewhere.