Strong paramagnetism and possible ferromagnetism in pure carbon nanofoam produced by laser ablation

Abstract

We report the production of a hierarchically nanostructured magnetic carbon foam by high-repetition-rate laser ablation of glassy carbon in Ar. The clusters contain both sp2 and sp3 bonded carbon atoms. The material contains graphite-like sheets with hyperbolic curvature, as proposed for "schwarzite". In addition to other unusual properties, the all-carbon nanofoam exhibits para- and maybe ferromagnetic behavior up to 90 K, with a narrow hysteresis curve, susceptibility of the order of 10-5 emu/g Oe, and a high saturation magnetization (up to 0.8 emu/g at 1.8 K). We postulate that localized unpaired spins occur because of topological and bonding defects associated with the sheet curvature, and that these spins are stabilized for >1 year due to the steric protection offered by the convoluted sheets. © 2004 Elsevier B.V. All rights reserved.