2002 Fiscal Year Final Research Report Summary
Unconventional Magnetism of Nanographite and Molecular Devices
| Project/Area Number |
13440208
|
|---|
| Research Category |
Grant-in-Aid for Scientific Research (B)
|
| Allocation Type | Single-year Grants |
|---|
| Section | 一般 |
|---|
| Research Field |
機能・物性・材料
|
|---|
| Research Institution | Tokyo Institute of Technology |
|---|
Principal Investigator |
ENOKI Toshiaki Tokyo Institute of Technology, Graduate school of Science and Engineering, Professor, 大学院・理工学研究科, 教授 (10113424)
|
|---|
| Co-Investigator(Kenkyū-buntansha) |
HARIGAYA Kikuo Nanotechnology Research Institute, National Institute of Advanced Industrial Science and Technology, Researcher, ナノテクノロジー研究部門, 主任研究員 (00357823)
TAKAI Kazuyuki Tokyo Institute of Technology, Graduate school of Science and Engineering, Research Associate, 大学院・理工学研究科, 助手 (80334514)
FUKUI Kenichi Tokyo Institute of Technology, Graduate school of Science and Engineering, Assistant professor, 大学院・理工学研究科, 助教授 (60262143)
|
|---|
| Project Period (FY) |
2001 – 2002
|
| Keywords | nanographite / edge state / molecular magnet / diamond-like carbon / electron wave diffraction / scanning tunneling microscope / sp^2 / sp^3 mixed carbon / nanodiamond |
|---|
| Research Abstract |
Nano-sized graphene (mono-layer graphite) is an interesting molecule-based nanoscopic magnetic system, in which a variety of unique magnetic features appear in relation to its secific electronic structure. We investigated magnetic properties of nano-graphene and networked nano-graphites using activated carbon fibers (ACF) and nano-graphite prepared by heat-treatment of nano-diamond particles. The nano-graphite obtained from nano-diamond particle forms a polyhedron with a hollow inside, where each facet comprises a stacking of 3-6 nano-graphene sheets with the mean size of 7nm. ACFs are featured with a 3D network of nano-grsphite domains, where each domain is formed with a stacking of 3-4 graphene sheets with the mean size of 2-3nm. The electronic features of ACFs are characterized as Anderson insulator in the Coulomb gap variable hopping regime. In the 3D nano-graphite network in ACFs, where each nano-graphite domain has ca.1 spin, the magnetic properties governed by the edge-state spi
… More
ns obey the Curie-Weiss law with a small negative Weiss temperature of -2-4K. The physisorption of guest species such as water or ethanol into the nano-space (micropore) surrounding nano-graphite domains brings about a discontinuous drop in the magnetic moment of the edge spin at a threshold amount of guest species. Judging from the fact that guests accommodated in micropores squeeze nano-graphites, which makes the inter-graphene layer distance shrunk, this can be explained with the internal-pressure-induced enhancement of the exchange interaction between nano-graphenes. Heat-treatment induces an insulator-metal transition around 1300℃, above which the magnetism can be described in terms of Pauli paramagnetism. Here, the development of an infinite percolation path network is responsible for the metallic state. In the vicinity of the insulator-metal transition, a novel disordered magnetism similar to spin-glass state appears below ca.7K due to the randomness in the strengths of exchange interactions between non-bonding π edge-state spins, which are mediated by the conduction π-electrons. The experimental findings presented above reveal novel nanoscopic magnetism of nano-graphite-based molecular magnets. We could also successfully prepare a single nano-graphene sheet on a graphite substrate by heat-treatment of a nanodiamond particle after electrophoretic treatment. A nano-graphite with its layer tilted with respect to the substrate show an electron diffraction pattern with the periodicity varying along the tilting direction. Less
|
