Magnetic excitations in Cu6 and Mn6 hexagons embedded in D3d-symmetric polyoxotungstates.
Magnetic excitations in Cu6 and Mn6 hexagons embedded in D3d-symmetric polyoxotungstates.
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DOI：
10.1002/chin.200801013
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发表时间：
2007-09
影响因子：
4.6
通讯作者：
N. Zamstein;Alex Tarantul;B. Tsukerblat
中科院分区：
文献类型：
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作者：
N. Zamstein;Alex Tarantul;B. Tsukerblat
在这篇文章中，我们重新考虑了两个新的多钨酸盐的磁性测量的讨论，（n-BuNH（3））（12）[（CuCl）（6）（AsW（9）O（33））（2）]·6H（2）O和（n-BuNH（3））（12）[（MnCl）（6）（SbW（9）O（33））（2）]. 6 H（2）O，已由Yamase等人合成并表征（Inorg.Chem. 2006，45，7698）。基于各向同性交换哈密顿量的精确对角化方法，对Cu（6）（12+）和Mn（6）（12+）六角体的磁化率和磁化强度进行了分析，结果表明，最佳拟合的第一近邻耦合参数分别为J = 35和0.55 cm（-1），而第二近邻相互作用很小.这些值大大超过Yamase等人根据不适用于六元环的Kambe-Van Vleck公式获得的值（J = 8.82和0.14 cm（-1））。在1.8K下，磁化强度的场依赖性与实验数据也得到了很好的拟合。结果表明轴向各向异性的重要性，这是特别明显的Mn（6）（12+）集群。我们还讨论了交换多重态的对称性分配的确切SGamma条款（全自旋，S，和不可约表示，伽玛，的点群）和相关的结果与选择规则的各向异性磁贡献。反对称交换作为一阶扰动出现在轨道简并多重态中，并产生沿沿着C（6）轴的易磁化轴。塞曼能级的评估表明，在六边形的平面中施加的场完全降低了反对称交换的影响。
In this article we reconsider the discussion of the magnetic measurements for the two novel polyoxotungstates, (n-BuNH(3))(12)[(CuCl)(6)(AsW(9)O(33))(2)].6H(2)O and (n-BuNH(3))(12)[(MnCl)(6)(SbW(9)O(33))(2)].6H(2)O, which have been synthesized and characterized by Yamase et al. (Inorg.Chem. 2006, 45, 7698). Analysis of the magnetic susceptibility and magnetization for Cu(6)(12+) and Mn(6)(12+) hexagons based on the exact diagonalization of isotropic exchange Hamiltonian shows that the best-fit first-neighbor coupling parameters are J = 35 and 0.55 cm(-1), respectively, while the second-neighbor interactions are very small. These values exceed considerably those obtained by Yamase et al. (J = 8.82 and 0.14 cm(-1)) on the basis of the Kambe-Van Vleck formula that is inappropriate for six-membered rings. We also got perfect fits to the experimental data for the field dependence of magnetization at 1.8 K. The results imply the importance of axial anisotropy, which is shown to be especially pronounced for the Mn(6)(12+) cluster. We discuss also the symmetry assignments of exchange multiplets to the exact SGamma terms (full spin, S, and irreducible representation, Gamma, of the point group) and correlate the results with the selection rules for the anisotropic magnetic contributions. The antisymmetric exchange is shown to appear in orbitally degenerate multiplets as a first-order perturbation and gives rise to an easy axis of magnetization along the C(6) axis. Evaluation of the Zeeman levels shows that the field applied in the plane of the hexagon fully reduces the effect of the antisymmetric exchange.