Positive magnetisation in carbon nanostructures

Carbon nanoclusters produced by high-repetition-rate laser ablation of glassy carbon in Ar exhibits para- and ferromagnetic behaviour up to 90 K, showing a narrow hysteresis curve with a coercive force Hc = 420 Oe, remnant magnetisation of 5 × 10−3 emu/g, susceptibility of the order of 10−5 emu/g Oe and saturation magnetization 0.3–0.8 emu/g at 1.8 K. We consider briefly the mechanism of formation of clusters in the laser-ablated vapour and structural characteristics of the nanoclusters, which show the presence of graphite-like sheets with hyperbolic curvature, as proposed for “schwarzite”. 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.