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Unconventional Magnetism of Nanographite and Molecular Devices

纳米石墨和分子器件的非常规磁性

基本信息

批准号：
13440208
负责人：
ENOKI Toshiaki
金额：
$ 9.41万
依托单位：
Tokyo Institute of Technology
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (B)
财政年份：
2001
资助国家：
日本
起止时间：
2001 至 2002
项目状态：
已结题

项目摘要

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

纳米石墨烯（单层石墨）是一种有趣的基于分子的纳米级磁性系统，其中出现了与其特定电子结构相关的各种独特的磁性特征。我们使用活性碳纤维（ACF）和纳米金刚石颗粒热处理制备的纳米石墨，研究了纳米石墨烯和网络纳米石墨的磁性能。由纳米金刚石颗粒得到的纳米石墨形成内部中空的多面体，每个面由3-6片平均尺寸为7nm的纳米石墨烯片堆叠而成。 ACF 具有纳米石墨烯域的 3D 网络，其中每个域由 3-4 个平均尺寸为 2-3 nm 的石墨烯片堆叠而成。 ACF 的电子特征被描述为库仑间隙可变跳跃区域中的安德森绝缘体。在 ACF 的 3D 纳米石墨网络中，每个纳米石墨域具有约 1 个自旋，由边缘态 spi 控制的磁特性遵循居里-韦斯定律，负韦斯温度为 -2-4K。客体物质（例如水或乙醇）物理吸附到纳米石墨域周围的纳米空间（微孔）中，导致客体物质阈值量下边缘自旋磁矩的不连续下降。从微孔中容纳的客体挤压纳米石墨，使石墨烯层间距离缩小来看，这可以用内压引起的纳米石墨烯之间交换相互作用的增强来解释。热处理在1300℃左右引起绝缘体-金属转变，高于此温度可以用泡利顺磁性来描述磁性。在这里，无限渗透路径网络的发展是金属态的原因。在绝缘体-金属转变附近，由于非键合 π 边缘态自旋之间的交换相互作用强度的随机性（由传导 π 电子介导），在约 7K 以下出现了一种类似于自旋玻璃态的新型无序磁性。上述实验结果揭示了纳米石墨基分子磁体的新颖纳米磁性。我们还可以通过电泳处理后对纳米金刚石颗粒进行热处理，在石墨基板上成功制备单层纳米石墨烯片。其层相对于基底倾斜的纳米石墨显示出周期性沿倾斜方向变化的电子衍射图案。较少的