Carbon 40 (2002) 1825–1842 Magnetic interactions in carbon nanostructures a, a b a b b * C. Goze-Bac , S. Latil , P. Lauginie ,V. Jourdain , J. Conard , L. Duclaux , c a A. Rubio , P. Bernier a ´ GDPC, UMR 5581, Universite de Montpellier II, Place E. Batailon, 34095 Montpellier Cedex 5, France b ´ ´ ´ CRMD, CNRS, Universite Orleans, 45071 Orleans, France c Departmento de Fisica Teorica, Universidad Valladolid, Valladolid, Spain Received 12 June 2001; accepted 2 February 2002 Abstract A review is given of local and non-local magnetic interactions in carbon nanotubes as observed by NMR and EPR. Since reference to graphite and graphene is compulsory, an extended review of the NMR and EPR of graphite and related materials, including GIC, is given. Then EPR, and either static or high-resolution NMR experimental results, both in pure 13 and intercalated MWNT or SWNT, are then reviewed. From high-resolution C-NMR in association with a theoretical modelization, it is shown how conducting and semiconducting carbon nanotubes might be discriminated. The benefits of high-resolution NMR for the characterization of carbon nanotube functionalization are described. The strong interdependence of all carbon material studies is clearly highlighted throughout the paper.  2002 Published by Elsevier Science Ltd. Keywords: A. Carbon nanotubes; C. Nuclear magnetic resonance, Electron spin resonance, Modeling; D. Magnetic properties 1. Introduction chemical shift tensor in SWNT: it describes a promising test allowing discrimination between conducting and In this review, carbon nanotubes will essentially be semiconducting nanotubes. considered from the point of view of those electronic Graphite can be considered as a reference material for properties which can be probed through NMR and EPR, the study of either carbon nanotubes or fullerenes: for 13 i.e. electron–nucleus magnetic interactions. Since carbon C-NMR, which yields very local tests of the electronic nanotubes can be considered as rolled graphene sheets, i.e. structure, those materials can fundamentally be considered extended 2D hexagonal arrays, and taking into account the as being constructed from graphene sheets slightly per- 13 relative complexity of C-NMR interpretation, Section 2 turbed by 1D or 2D curvature, respectively, resulting in 3 is devoted to a review of the background of NMR studies partial sp hybridization. in graphite and graphite intercalated compounds (GIC). The specific electronic properties of graphite arise from 13 Indeed, previous C studies have provided a clear status the quasi-degeneracy of the p and p* bands at the K-point for the ‘graphene plane’, and, from GIC studies, a very of the c-parallel edge of the Brillouin zone: graphite is a useful scaling of the isotropic and anisotropic metallic (or quasi-semi-metal, with both a very low carrier density and Knight) shifts in conductive carbon species. EPR and static a very low density of states at the Fermi level (so-called 13 C-NMR in pristine and alkali-intercalated multiwall ‘Fermi-DOS’), while graphene is an idealized 2D model of nanotubes (MWNT) are reviewed in Section 3. In Section a perfect one. Viewed more physically, those properties 13 4, EPR, static and high-resolution C-NMR studies of result from the high in-plane delocalization of p electrons, pure and functionalized SWNT are considered. Section 4.4 thus generalizing the ‘London ring currents’ well-known in 13 presents a recent theoretical modelization of the C aromatic materials. In this respect, a graphene plane is an infinitely extended aromatic molecule. Such delocalization and degeneracies result in very specific electronic prop- *Corresponding author. Tel.: 133-4-6714-3598; fax: 133-4- erties which are typical of graphite, i.e.: 6714-4637. E-mail address: goze@gdpc.univ-montp2.fr (C. Goze-Bac). 0008-6223 / 02 / $ – see front matter  2002 Published by Elsevier Science Ltd. PII: S0008-6223(02)00061-1