Abstract Submitted to the    NANOTUBE'06 Conference:

Edge state and unconventional magnetism of nanographene/nanographite

Toshiaki Enoki

Tokyo Institute of Technology

tenoki@chem.titech.ac.jp

XX. Magneto-Transport and Magnetism

Nanographene, defined as nano-sized flat hexagon network having open edges, has edge-shape-dependent electronic structure, where, according to theoretical prediction, nonbonding pai-electron state (edge state) created around zigzag edges causes unconventional magnetism in nanographene or nanographite. We investigated the electronic structure of graphene edges in atomic resolution, and the magnetic features of activated carbon fibers (ACFs) which consist of disordered network of nanographite domains. UHV-STM/STS observations for zigzag edges with their edge carbon atoms hydrogen-terminated prove the presence of large local density of states populated in the edge region and a sharp density-of-states peak around the Fermi energy, in contrast to the absence of these features in the armchair edges. This importantly imparts experimental evidence of edge state as the origin of spin magnetism, which appears as unconventional magnetic features in nanographene or nanographite. Magnetic investigations demonstrate spin glass state of edge-state spins in the metal-insulator threshold in disordered network of nanographite domains. Host-guest interaction modifies the magnetic features of nanographite domains. Water adsorption in nanopores of ACFs shows a high-spin/low-spin magnetic switching phenomenon, in which a discontinuous reduction takes place in the magnetic moment at a threshold water vapor pressure when the nanopores are filled with water molecules.

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