Magnetic ordering and spin-glass behaviour of carbon nanoclusters

Carbon nanoclusters produced by high-repetition-rate laser ablation of graphite and glassy carbon in Ar exhibits para- and ferromagnetic behaviour at low temperature. The results show that the degree of remanent order is strongly dependent on the magnetic history, i.e. whether the samples were cooled under zero-field or field conditions. Such behaviour is typical for a spin glass structure where the system can exist in many different roughly equivalent spin configurations. The spin-freezing temperature is unusually high (50-300 K) compared with < 15 K for typical spin glasses. The maximum in the zero-field magnetic susceptibility experiments and their field dependence indicate that there is competition between ferromagnetic and antiferromagnetic exchange pathways, accounting for the spin glass behavior and/or a low-dimensionality of the system.