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Spin Glass Behaviour of Magnetic Carbon Nanoclusters

A.V. Rode, A.G. Christy, N.R. Madsen, E.G. Gamaly, B. Luther-Davies, D. Arcon, A. Zorko and Z. Jaglicic
The Australian National University, AU

Keywords:
paramagnetic carbon nanoclusters, schwarzite, carbon nanofoam

Abstract:
Carbon nanoclusters produced by high-repetition-rate laser ablation of graphite and glassy carbon in Ar exhibits para- and ferromagnetic behavior up to 90 K, showing a narrow hysteresis curve with a coercive force Hc = 420 Oe, remnant magnetisation of 510-3 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.
The variety of different atomic scale bonding geometries and nanoscale structures gives us the possibility to tailor the electronic and magnetic properties of carbon-derived materials. Astonishingly, ferromagnetic behaviour has been reported in a number of different carbon systems even at room temperature bringing carbon-based ferromagnetism from dreams to reality. In this report we will focus on the ferromagnetic transition in carbon nanofoam. Magnetic properties of different carbon nanofoams were studied by susceptibility measurements and by electron paramagnetic resonance. We will discuss the origin of magnetic moment in a connection with the structure as well as the origin of the ferromagnetic exchange interactions.

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