13 C NMR and EPR of carbon nanofoam

Abstract

The 13C NMR spectra of a carbon nanofoam sample, exhibiting a peak in the ZFC magnetic susceptibility, show a single 13C line at room temperature and a two peak structure at 100 K. The splitting and the NMR shifts are however much too small to be associated with true ferromagnetism as for instance observed in TDAE-C60 below TC. The X-band EPR spectra show the presence of a least three different paramagnetic clusters with ga = 2.0016, gb = 2.0031, gc = 2.0036 and very different electronic spin-lattice relaxation times. In some samples the CW EPR spectra show an additional rather broad and strongly temperature dependent line shifted to lower fields, which is characteristic of ferromagnetic systems. The results thus show an inhomogeneous super-paramagnetic or spin-glass like nature of magnetism in cluster assembled carbon nanofoam rather than homogeneous ferromagnetism. Show more