Local Ferromagnetism in Microporous Carbon with the Structural Regularity of Zeolite Y

Magnetization M(H,T) measurements have been performed on microporous carbon (MC) with a three-dimensional nano-array structure corresponding to that of a zeolite Y supercage. The obtained results unambiguously demonstrate the occurrence of high-temperature ferromagnetism in MC, probably originating from a topological disorder associated with curved graphene sheets. The results provide evidence that the ferromagnetic behavior of MC is governed by isolated clusters in a broad temperature range, and suggest the occurrence of percolative-type transition with the temperature lowering. A comparative analysis of the results obtained on MC and related materials is given.Comment: To be published in Physical Review B (2003

Magnetic nanographite

Hydrogenated nanographite can display spontaneous magnetism. Recently we proposed that hydrogenation of nanographite is able to induce finite magnetization. We have performed theoretical investigation of a graphene ribbon in which each carbon is bonded to two hydrogen atoms at one edge and to a single hydrogen atom at another edge. Application of the local-spin-density approximation to the calculation of the electronic band-structure of the ribbon shows appearance of a spin-polarized flat band at the Fermi energy. Producing different numbers of mono-hydrogenated carbons and di-hydrogenated carbons can create magnetic moments in nanographite.Comment: 4 pages, 3 Postscript figures, uses revtex4.cls, submitted to Phys. Rev.

Structural Studies Of Magnetic Polymerized Fullerene

X-ray and Raman measurements have been performed on samples of polymerized fullerenes, which show weak ferromagnetism. For pressure-polymerized fullerenes, ferromagnetic features are observed in a narrow temperature range very close to the limit of stability of the cages. Raman spectra show that the type of polymerization is probably of less importance. Strong structural inhomogeneity of the samples suggests that the magnetic phase forms a minority phase in a non-magnetic matrix.13701/03/1513351337Rao, A.M., Zhou, P., Wang, K.A., Hager, G.T., Holden, J.M., Wang, Y., Lee, W.T., Amster, I.J., (1993) Science, 259, p. 955Iwasa, Y., Arima, T., Fleming, R.M., Siegrist, T., Zhou, O., Haddon, R.C., Rothberg, L.J., Yagi, T., (1994) Science, 264, p. 1570Sundqvist, B., (1999) Adv. Phys., 48, p. 1Makarova, T.L., Liu, B.-B., Sundqvist, B., (2001) AIP Conference Proceedings, 591, p. 57Murakami, Y., Suematsu, H., (1996) Pure Appl. Chem., 68, p. 1463Makarova, T.L., Sundqvist, B., Esquinazi, P., Höhne, R., Kopelevich, Y., Scharff, P., Davydov, V.A., Rakhmanina, A.V., (2001) Nature, 413, p. 716Wood, R.A., Lewis, M.H., Lees, M.R., Bennington, S.M., Cain, M.G., Kitamura, N., (2002) J. Phys.: Condens. Matter, 14, pp. L385Moret, R., Launois, P., Wågberg, T., Sundqvist, B., (2000) Eur. Phys. J. B, 15, p. 253Blank, V.D., Buga, S.G., Dubitsky, G.A., Serebryanaya, N.R., Popov, M.Yu., Sundqvist, B., (1998) Carbon, 36, p. 319Makarova, T.L., Scharff, P., Sundqvist, B., Gaevski, M.E., Davydov, V.A., Rakhmanina, A.V., Kashevarova, L.S., (2001) Carbon, 39, p. 220

Graphene nanochains and nanoislands in the layers of room-temperature fluorinated graphite

International audienceIntercalated compound of graphite fluoride with n-heptane has been synthesized at room temperature using a multi-stage process including fluorination by a gaseous BrF3 and a set of intercalant exchange reactions. It was found that composition of the compound is CF0.40(C7H16)0.04 and the guest molecules interact with the graphite fluoride layers through the van der Waals forces. Since the distance between the filled layers is 1.04 nm and the unfilled layers are separated by ∼0.60 nm, the obtained compound can be considered as a stack of the fluorinated graphenes. These fluorinated graphenes are large in area making it possible to study local destruction of the π conjugated system on the basal plane. It was shown that fluorine atoms form short chains, while non-fluorinated sp2 carbon atoms are organized in very narrow ribbons and aromatic areas with a size smaller than 3 nm. These π electron nanochains and nanoislands preserved after the fluorination process are likely responsible for the value of the energy gap of the compound of ∼2.5 eV. Variation in the size and the shape of π electron regions within the fluorinated graphene layers could be a way for tuning the electronic and optical characteristics of the graphene-based materials

Testing the magnetism of polymerized fullerene

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Magnetic Carbon

The discovery of nanostructured forms of molecular carbon has led to renewed interest in the varied properties of this element. Both graphite and C 60 can be electron-doped by alkali metals to become superconducting; transition temperatures of up to 52 K have been attained by field-induced hole-doping of C 60 (ref. 2). Recent experiments and theoretical studies have suggested that electronic instabilities in pure graphite may give rise to superconducting and ferromagnetic properties, even at room temperature. Here we report the serendipitous discovery of strong magnetic signals in rhombohedral C 60. Our intention was to search for superconductivity in polymerized C 60; however, it appears that our high-pressure, high-temperature polymerization process results in a magnetically ordered state. The material exhibits features typical of ferromagnets: saturation magnetization, large hysteresis and attachment to a magnet at room temperature. 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Magnetism of aniline modified graphene-based materials

The possibility of producing magnetic graphene nanostructures by functionalization with aromatic radicals has been investigated. Functionalization of graphene basal plane was performed with three types of anilines: 4-bromoaniline, 4-nitroaniline and 4-chloroaniline. The samples were examined by composition analysis with energy-dispersive X-ray spectroscopy and magnetic measurements by SQUID magnetometry and electron paramagnetic resonance. Initial graphene was produced by thermal exfoliation. Both pristine and functionalized samples demonstrate strong paramagnetic contribution at low temperatures, which originates from intrinsic defects. Attachment of an organic molecule with the formation of a covalent bond with carbon atom on the basal plane generates a delocalized spin in the graphene π - electron system. Nitroaniline proved to be the most suitable and sufficiently reactive to attach to the basal plane carbon atoms in large amounts. Functionalization of graphene with nitroaniline resulted in appearance both ferromagnetic and antiferromagnetic features with a clear antiferromagnetic transition near 120 K