Electronic properties of carbon nanohorns studied by ESR

The magnetic properties of carbon nanohorns were investigated by electron s pin resonance. Two decoupled electronic systems were found. The first one, which has a spin susceptibility linearly varying with temperature, was tent atively attributed to two-dimensional graphenelike sheets. The second contr ibution, showing a Curie-like behavior with a non-negligible Pauli part, wa s ascribed to the interior of the structures of coagulated nanohorns. Surpr isingly, this second line shows a strong suppression of susceptibility at 1 7 K. Due to a concomitant line broadening and g shift below 17 K, this tran sition was assigned to antiferromagnetic pairing of localized spins; The lo w spin concentration is implying that a kind of magnetism, mediated by the free spin carriers, has to be invoked to explain the phenomenon.