BeltlikeC60−Electron Spin Density Distribution in the Organic Ferromagnet TDAE-C60<

Abstract

The observed huge increase in the width of the (3C)NMR spectra of TDAE-C(0 )n the middle of the ferromagnetic phase at 10 K is due to a Jahn-Teller distortion of the C(60 )(-) which becomes visible in view of the resulting changes in the Fermi contact electron-(13)C NMR shifts. The shape of the (13)C spectra allows for a direct determination of the belt-like redistribution of the unpaired electron spin density on the C(60)(-) ions, which is responsible for the relatively high ferromagnetic transition temperature in this purely organic system.

Origin of magnetic moments in carbon nanofoam

“…The low loss region contains plasmon loss peaks, which were used to approximate the volume density. 25 The individual cluster density was found to be in the range 1.55-1.90 g / cm 3 , close to our earlier estimate of 1.9 g / cm 3 . 17 EPR measurements were performed on a commercial Bruker E580 spectrometer.…”

“…The fraction of sp 3 bonded carbon atoms was calculated from the carbon K edge 24 assuming that ͑sp 2 + sp 3 ͒ = 100%. The sp 3 content was found to be in the range 8-20%, the results for particular samples are presented in Table I. There was no clear dependence of the proportion of sp 3 bonding or the cluster size on the Ar pressure in the experiments.…”

“…Irradiation by protons of energy 2.25 MeV on highly oriented pyrolitic graphite has been shown to trigger room temperature ferromagnetism. 13 In this case ferromagnetism was associated with the mixed sp 3 -sp 2 structure stabilized by mono-and dihydrogenated carbon atoms 13,14 or monohydrogenated edges. 15 Ferromagnetism thus occurs in quite different carbonderived systems, but it is still unclear which are the most crucial factors in the process of stabilization of magnetic moments and promotion of exchange interactions.…”

Jahn–Teller orbital glass state in the expanded fcc Cs3C60 fulleride

“…4 This coincides with the results of the IR experiments, 11 which derived the upper limit of the difference in energy of competing JT conformers as 2.4 meV (28 K). The present MAS NMR results thus establish fully the energy landscape for the C 60 3− JT deformations in fcc Cs 3 C 60 : the larger energy scale of 68 (15) meV is the energy barrier required for the thermally excited jumps between different JT conformers whose energies differ by only 2.4 meV. Although the onset of the static JT effect will lead to the loss of the stabilization energy associated with delocalization of the distortion orientation, the static component will remain 13 providing an energy gain associated with the splitting of t 1u levels in the local orientationally-disordered environment.…”

“…15,16 For instance, the JT-driven deformation of C 60 3− with the highest possible orthorhombic site symmetry (mmm) has D 2h symmetry 11,42 would show 9 individual 13 C NMR lines, i.e. the C1-C3 peaks would split further into three components each.…”