Study of quantum magnetism in nano spin polyhedrons

自旋多面体是具有高对称性的反铁磁自旋团簇。各种各样的磁网络是可能的，因为在这样的集群中不需要平移对称性。我们研究了两种类型的簇合物Mo 72 Fe 30和Fe 9。前者是所谓的三角形的角共享网络，后者是边共享网络。Mo_（72）Fe_（30）在1/3全磁化强度处出现了一个导数磁化倾角，并用“有序-无序”机制解释了其成因。在低温下，系统在比热和ESR谱线宽度上表现出广泛的异常。这一现象被解释为团簇内磁关联饱和引起的“准长程有序”。对于尺寸效应，在Mo_（72）Fe_（30）中证实了磁化台阶的拖尾效应，其中分立能级之间的能量分离小于混合项，如交错场和反对称交换相互作用。另一方面，在Fe_9中发现了明显的阶梯，阶梯磁化强度的降低归因于自旋手征引起的非对称混合。发现了明显的绝热磁化和半阶磁化现象，并对双核配合物和稀土团簇的磁化过程进行了比较。自旋手征性的重要性，在各种系统，如自旋管检查。

Spin polyhedrons are antiferromagnetic spin clusters of high symmetry without disorders. Variety of magnetic networks is possible because a translational symmetry in not needed in such clusters. We have investigated two types of clusters Mo72Fe30 and Fe9. The former cluster is so called corner-sharing network of triangles and latter is the edge-sharing network. The spin frustration is strong and the energy state is highly degenerated.The Mo72Fe30 shows a dip of derivative magnetization at the 1/3 of full magnetization and the origin of dip has been interpreted by the "order by disorder" mechanism. At low temperature, the system shows a broad anomaly in specific heat and in ESR line width. This phenomenon is interpreted as "quasi long range order" caused by the saturation of intra-cluster magnetic correlation. As for the size effect, the smearing of magnetization step is confirmed in Mo72Fe30, where the energy separation among the discrete levels is smaller than the mixing term such as staggered fields and anti-symmetric exchange interaction. On the other hand, clear steps are found in Fe9 and the reduction of the step magnetization is attributed to the asymmetric mixing caused by the spin chirality.The dynamics of the triangle spin ring, which is an important component of spin polyhedrons, has been investigated. A clear adiabatic magnetization and half-step magnetization phenomenon is found. The comparison of magnetization process is made with different systems such as two-nuclear complex and rare earth based cluster. The importance of spin chirality is examined in various system such as spin tube.