Structural distortions in the spin-gap regime of the quantum antiferromagnet SrCu2(BO3)2
Structural distortions in the spin-gap regime of the quantum antiferromagnet SrCu2(BO3)2
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量子反铁磁体 SrCu2(BO3)2 自旋能隙区域的结构畸变
DOI：
10.1016/j.jssc.2009.09.017
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发表时间：
2008
影响因子：
3.3
通讯作者：
A. Zorko
中科院分区：
文献类型：
--
作者：
C. Vecchini;O. Adamopoulos;L. Chapon;A. Lappas;H. Kageyama;Y. Ueda;A. Zorko
本文首次报道了二维阻挫反铁磁体SrCu_2（BO_3）_2在低温（<40 K）自旋带隙区的晶体学研究。晶体系统不偏离四氢I-42 m空间群对称性。然而，我们的高分辨率中子粉末衍射测量揭示了微妙的结构修改低于34 K，伴随着二聚体单重基态的形成。紧密的自旋-晶格耦合导致四元结构的负热膨胀，这反映到特定的局部晶格调整中。提取的结构参数表明减少的屈曲发现在铜硼酸盐平面和加强的领导，面内二聚体超交换相互作用。观察到的收缩沿着的c轴，与相邻层中的二聚体间的交换，表明参与较弱的三维相互作用的磁性。晶体对称性的规则并不排除Dzyaloshinsky-Moriya相互作用，因此仍然是自旋各向异性的重要来源，需要合理化的基态行为。
We report the first crystallographic study within the low-temperature (<40K) spin-gap region of the two-dimensional frustrated antiferromagnet SrCu2(BO3)2. The crystal system does not deviate from the tetragonal I-42m space group symmetry. However, our high-resolution neutron powder diffraction measurements uncover subtle structural modifications below 34K, concomitant to the formation of the dimer singlet ground state. Intimate spin–lattice coupling leads to negative thermal expansion of the tetragonal structure, which reflects into particular local lattice adjustments. The extracted structural parameters suggest the reduction of the buckling found in the copper–borate planes and the strengthening of the leading, in-plane intra-dimer superexchange interaction. The observed contraction along the c-axis, associated with the inter-dimer exchange in adjacent layers, indicates the involvement of weaker three-dimensional interactions in the magnetic properties. The rules posed by the crystal symmetry do not preclude Dzyaloshinsky–Moriya interactions, which therefore remain as an important source of spin anisotropy necessary to rationalise the ground state behaviour.