arXivDaily arXiv每日学术速递 周一至周五更新
arXiv 1303.4063cond-mat.str-el
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CuX2阻挫链(X = F,Cl,Br)的磁性:共价性的作用

Magnetism of CuX2 frustrated chains (X = F, Cl, Br): the role of covalency

S. Lebernegg, M. Schmitt, A. A. Tsirlin, O. Janson, H. Rosner

摘要:

采用周期性和团簇密度泛函理论(DFT)计算,包括DFT+U和杂化泛函,研究了自旋1/2阻挫链化合物CuX 2:CuCl 2,CuBr 2和一个虚构的链结构CuF 2的磁结构关联.最近邻和第二邻交换积分,J1和J2,作为一个功能的Cu-X-Cu桥接角,θ,在物理相关的范围80- 110度。在离子CuF_2中,当θ小于100 °时,J_1是铁磁性的。对于较大的角度,反铁磁超交换的贡献成为主导,符合古德诺-Kanamori-安德森规则。然而,CuCl 2和CuBr 2在整个研究的角度范围内都具有铁磁性J1。这种令人惊讶的行为归因于在Cl和Br化合物中增加的共价性,这放大了来自Hund交换对配体原子的贡献,并使J1具有铁磁性。同时,X轨道的空间扩展增强了反铁磁J2,这是通过Cu-X-X-Cu长程轨道实现的。这两个,周期性和集群的方法提供了一个一致的描述的磁性行为,这是在良好的协议与CuCl 2和CuBr 2的实验数据。因此,由于它们的简单性,集团计算有很好的潜力,研究磁相关性在更多涉及的自旋晶格和促进应用的量子化学方法。

英文摘要:

Periodic and cluster density-functional theory (DFT) calculations, including DFT+U and hybrid functionals, are applied to study magnetostructural correlations in spin-1/2 frustrated chain compounds CuX2: CuCl2, CuBr2, and a fictitious chain structure of CuF2. The nearest-neighbor and second-neighbor exchange integrals, J1 and J2, are evaluated as a function of the Cu-X-Cu bridging angle, theta, in the physically relevant range 80-110deg. In the ionic CuF2, J1 is ferromagnetic for theta smaller 100deg. For larger angles, the antiferromagnetic superexchange contribution becomes dominant, in accord with the Goodenough-Kanamori-Anderson rules. However, both CuCl2 and CuBr2 feature ferromagnetic J1 in the whole angular range studied. This surprising behavior is ascribed to the increased covalency in the Cl and Br compounds, which amplifies the contribution from Hund's exchange on the ligand atoms and renders J1 ferromagnetic. At the same time, the larger spatial extent of X orbitals enhances the antiferromagnetic J2, which is realized via the long-range Cu-X-X-Cu paths. Both, periodic and cluster approaches supply a consistent description of the magnetic behavior which is in good agreement with the experimental data for CuCl2 and CuBr2. Thus, owing to their simplicity, cluster calculations have excellent potential to study magnetic correlations in more involved spin lattices and facilitate application of quantum-chemical methods.

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