Unconventional Magnetism of Nanographite and Molecular Devices

纳米石墨烯(单层石墨)是一种有趣的基于分子的纳米磁性体系，与其特定的电子结构相关联，呈现出各种独特的磁性特征。我们使用活性碳纤维(ACF)和纳米石墨对纳米金刚石颗粒进行热处理，研究了纳米石墨烯和网状纳米石墨烯的磁性。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，每个面片由3-6片平均尺寸为7 nm的纳米石墨烯堆叠而成。ACF具有纳米钙钛矿结构域的3D网络，每个结构域由平均尺寸为2-3 nm的3-4片石墨烯堆积而成。ACF的电学特性表现为库仑能隙变跳跃区的Anderson绝缘体。在ACF中的3D纳米石墨网络中，其中每个纳米石墨结构域具有约1个自旋，其磁性质由边缘态Spi…控制更多的ns服从居里-魏斯定律，魏斯温度为-2-4K。客体物种，如水或乙醇的物理吸附到纳米石墨结构域周围的纳米空间(微孔)中，导致在客体物种阈值数量处边缘自旋的磁矩不连续地下降。从微孔中容纳的客体对纳米石墨烯的挤压，使得石墨烯间的层间距变小来看，这可以用内压诱导增强纳米石墨烯之间的交换作用来解释。热处理在1300℃附近引起绝缘体-金属相变，高于此相变的磁性可以用泡利顺磁性来描述。在这里，无限渗流路径网络的发展是金属状态的原因。在绝缘体-金属转变附近，由于非成键π边态自旋之间的交换作用强度的随机性，在约7K以下出现了类似于自旋玻璃态的新的无序磁性，这些交换作用是由传导π电子介导的。上述实验结果揭示了纳米石墨基分子磁体的新型纳米磁性。我们还可以通过对经过电泳处理的纳米金刚石颗粒进行热处理，在石墨衬底上成功地制备出单一的纳米石墨烯薄片。层相对于衬底倾斜的纳米石墨呈现出周期性沿倾斜方向变化的电子衍射图。较少

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