Drastic effect of water-adsorption on the magnetism of carbon nanomagnets

Activated carbon fibers (ACFs), composed of nanometer-size fragments of graphite (nanographites), show pi-electron-based paramagnetism. Measurements of ESR and magnetic susceptibility revealed that adsorption of water molecules drastically suppresses the paramagnetism of ACFs. Considering also the structural change, this is interpreted in terms of a crossover from a paramagnetic state to a low-spin state of each nanographite due to a structural change of nanographite-network caused by internal pressure of adsorbed water molecules. This phenomenon serves us as a new method for in situ controlling of the condensed state of electrons in soft materials. (C) 2003 Elsevier Science Ltd. All rights reserved.