Unusual magnetism in a carbon foam

First synthesized a few years ago by a collaboration of researchers from Greece, Australia, and Russia, carbon nanofoam consists of carbon clusters that are, on average, 6 nm across and randomly interconnected into a weblike foam that is extremely lightweight (2–20 mg/cm³). In addition, it is a semiconductor. Now, the same collaboration has uncovered unconventional magnetic properties in its ethereal carbon froth. For starters, freshly produced carbon nanofoam is ferromagnetic: It is strongly attracted to a permanent magnet at room temperature. Next, the room-temperature ferromagnetic behavior decays after a few hours, but a weak remanent magnetic equilibrium is reached after several weeks and persists at cryogenic temperatures. The researchers suggest that the ferromagnetism arises from the separation of nanometer-scale conducting regions by regions of a different electronic structure. They also suggest that products with similarly unusual properties might be synthesized from different starting materials. A possible application of carbon nanofoam is in biomedicine, where tiny ferromagnetic clusters injected into blood vessels might improve magnetic resonance imaging. (A. V. Rode et al. , http://arXiv.org/abs/cond-mat/0310751 .)