Spacio-temporal Correlatins and Ground States in Strongly Frustrated Systems

本研究通过对模型化合物的磁测量和计算机模拟，揭示了强竞争系统中由于几何挫折引起的时空相关性和量子效应。研究的模型化合物包括具有磁链三角形晶格的CsNi(Fe)Cl_3和BaVS_3，具有菱形堆积三角形晶格的delafo_2型化合物CuFe_<0.95>Al_<0.05>O_2和A gNiO_2，具有Kagome晶格的SrCr_8Ga_4O_<19>，具有三角形Kagome晶格的Cu_9X_2(cpa)_6 nH_2O (X=F,Cl, Br)，具有三维角共享三角形晶格的β - mn和具有角共享四面体晶格的Y(Sc)Mn_2。这些模型化合物所观察到的基态可以分为几组。CsNi(Fe)C1_3和CuFe_<0.95> Al_<0.05>O_2由于邻近自旋之间的磁相互作用而表现出较远的有序，但由于自旋受挫而具有复杂的磁结构。在BayS3中，挫折导致轨道有序并伴有轨道简并。其他自旋玻璃具有冻结自旋的基态，这与传统自旋玻璃在大等负魏斯温度下不同。每种自旋冻结状态都有各自的特征。SrCr_8Ga_4O_<19>和Cu_6X2(cpa)_3 nH_2O的互易磁化率在比自旋冻结更高的温度下改变了温度梯度，表明由于量子效应形成了单线态。在β - mn和Y(Sc)Mn_2中发现的自旋冻结归因于晶格缺陷引起的矩的自旋冻结，并得出结论，这些化合物中的大多数自旋处于自旋液态。决定经典自旋冻结和量子冻结的条件仍然是未来的问题。

The present study was performed to reveal the spacio-temporal correlations and quantum effect in strongly competing systems due to geometrical frustration by means of magnetic measurements on model compounds and computer simulation. The studied model compounds include CsNi(Fe)Cl_3 and BaVS_3 with the triangular lattice of magnetic chains, delafossite type compounds CuFe_<0.95>Al_<0.05>O_2 and A gNiO_2 with the rhombohedrally stacked triangular lattice, SrCr_8Ga_4O_<19> with the Kagome lattice, Cu_9X_2(cpa)_6 nH_2O (X=F,Cl, Br) with the triangulated Kagome lattice, beta-Mn with the corner sharing triangle lattice in three dimension and Y(Sc)Mn_2 with the corner sharing tetrahedron lattice.The observed ground states of these model compounds may be divided in several groups. CsNi(Fe)C1_3 and CuFe_<0.95> Al_<0.05>O_2 exhibit long range orders due to magnetic interaction between further neighbor spins than the nearest but have complicated magnetic structures due to spin frustration. Frustration gives rize to an orbital ordering in BayS3 with orbital degeneracy. The others have ground states with frozen spins which are different from conventional spin glasses in negative Weiss temperature of large magnitude. Each spinfrozen state exhibits individual features. The reciprocal magnetic susceptibility of SrCr_8Ga_4O_<19> and Cu_6X2(cpa)_3 nH_2O change the temperature gradient at much higher temperature than the spin freezing indicating singlet formation due to quantum effect. The spin freezing found in beta-Mn and Y(Sc)Mn_2 was attributed to the spin freezing of moments induced by lattice defects and it was concluded that the majority spins in these compounds are in spin liquid state. The conditions which determine the classical spin freezing and the quantum freezing are still future problem.