EPR and magnetism of the nanostructured natural carbonaceous material shungite

Abstract

The X-band EPR and magnetic susceptibility in the temperature range 4.2-300 K study of the shungite-I, natural nanostructured material from the deposit of Shunga are reported. Obtained results allow us to assign the EPR signal to conduction electrons, estimate their number, N P , and evaluate the Pauli paramagnetism contribution to shungite susceptibility. A small occupation (*5%) of the localized nonbonding p states in the zigzag edges of the open-ended graphene-like layers and/or on r (sp 2?x) orbitals in the curved parts of the shungite globules has been also revealed. The observed temperature dependence of the EPR linewidth can be explained by the earlier considered interaction of conduction p electrons with local phonon modes associated with the vibration of peripheral carbon atoms of the open zigzag-type edges and with peripheral carbon atoms cross-linking different nanostructures. The relaxation time T 2 and diffusion time T D are found to have comparable values (2.84 9 10-8 and 1.73 9 10-8 s at 5.2 K, respectively), and similar dependence on temperature. The magnetic measurements have revealed the suppression of orbital diamagnetism due to small amount of large enough fragments of the graphene layers.

Thermodynamic and magnetic properties of surface Fe3+ species on quartz: effects of gamma-ray irradiation and implications for aerosol–radiation interactions

“…This temperature dependence of the EPR linewidth observed in the irradiated amethyst is attributable to interaction between conduction electrons and phonons (cf. Augustyniak-Jabłokow et al 2010). This interaction leads to a temperature-dependent spin-relaxation time on the order of *10 -8 s. The observed line broadening from 90 to 294 K is attributable to dipolar interactions (cf.…”

Preparation and characterization of partially reduced graphene oxide aerogels doped with transition metal ions

“…The EPR signals shape, intensity, g factor, linewidth, spin concentration is source of large number of information about local site symmetry, local dynamic and electron relaxation [50]. EPR study of graphene and graphene-related materials gives an important information about interactions and magnetism sources like defects, not passivated magnetic moments on edges, surface adatoms with unpaired magnetic moments, conduction electrons, and also remaining metal ion contamination [28,[51][52][53][54][55][56][57][58][59]. Unpaired electrons located on edges, on/in the graphene surface, are extremely sensitive to external conditions like atmosphere (oxygen, helium and vacuum) or moisture influencing the localization of Figure 7 Raman spectra of the reference and TMi-doped prGO aerogels.…”

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