Electronic properties of carbon nanohorns studied by ESR

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