Spin-orbit coupling and crystal-field distortions for a low-spin $3d^5$ state in BaCoO$_{3}$
Y. Y. Chin, Z. Hu, H. -J. Lin, S. Agrestini, J. Weinen, C. Martin, S. Hébert, A. Maignan, A. Tanaka, J. C. Cezar, N. B. Brookes, Y. -F. Liao, K. -D. Tsuei, C. T… 展开作者
Y. Y. Chin, Z. Hu, H. -J. Lin, S. Agrestini, J. Weinen, C. Martin, S. Hébert, A. Maignan, A. Tanaka, J. C. Cezar, N. B. Brookes, Y. -F. Liao, K. -D. Tsuei, C. T. Chen, D. I. Khomskii, L. H. Tjeng
We have studied the electronic structure of BaCoO$_3$ using soft x-ray absorption spectroscopy at the Co-$L_{2,3}$ and O-$K$ edges, magnetic circular dichroism at the Co-$L_{2,3}$ edges, as well as valence band hard x-ray photoelectron spectroscopy. The quantitative analysis of the spectra established that the Co ions are in the formal low-spin tetravalent 3$d^5$ state and that the system is a negative charge transfer Mott insulator. The spin-orbit coupling plays also an important role for the magnetism of the system. At the same time, a trigonal crystal field is present with sufficient strength to bring the 3$d^5$ ion away from the $J_{eff} = 1/2$ state. The sign of this crystal field is such that the $a_{1g}$ orbital is doubly occupied, explaining the absence of a Peierl's transition in this system which consists of chains of face-sharing CoO$_6$ octahedra. Moreover, with one hole residing in the $e_g^π$, the presence of an orbital moment and strong magneto-crystalline anisotropy can be understood. Yet, we also infer that crystal fields with lower symmetry must be present to reproduce the measured orbital moment quantitatively, thereby suggesting the possibility for orbital ordering to occur in BaCoO$_3$.
Anisotropic phonon conduction and lattice distortions in CMR-type bilayer manganite (La$_{1-z}$Pr$_{z}$)$_{1.2}$Sr$_{1.8}$Mn$_{2}$O$_{7}$ (z=0,0.2,0.4 and 0.6) single crystals
本文系统地研究了（La $_{1-z}$ Pr $_{z}$）$_{1.2}$ Sr $_{1.8}$ Mn $_{2}$ O $_{7}$（$z$（Pr）= 0.2，0.4）单晶的热导率随温度和磁场的变化。和0.6。晶格畸变由于Pr-取代和各向异性的热导率在双层锰氧化物中的不同的弛豫模型的基础上提出的金属和绝缘状态的局部晶格畸变的Maderda等。巨磁热效应的缩放作为磁化强度的函数，并讨论了由于Pr-取代的$e_g$ -电子轨道状态的占领的系统变化的基础上。
G-type antiferromagnetism and orbital ordering due to the crystal field from the rare-earth ions induced by the GdFeO_3-type distortion in RTiO_3 with R=La, Pr, Nd and Sm
Spontaneous lattice distortion and crystal field effects in HoB4
Institute of Physics of the Czech Academy of Sciences（捷克科学院物理研究所）；Hochfeld-Magnetlabor Dresden (HLD-EMFL) and Würzburg-Dresden Cluster of Excellence ct.qmat, Helmholtz-Zentrum Dresden-Rossendorf（德累斯顿强磁场实验室（HLD-EMFL）与维尔茨堡-德累斯顿卓越集群ct.qmat，亥姆霍兹德累斯顿-罗斯多夫中心）；Department of Condensed Matter Physics, Charles University（查理大学凝聚态物理系）；Department of Quantum Matter, AdSE, Hiroshima University（广岛大学量子物质研究中心（AdSE））；Department of Physics, University of Warwick（华威大学物理系）；National Physical Laboratory（英国国家物理实验室）；Institut fur Festkörper- und Materialphysik, TU Dresden（德累斯顿工业大学固体与材料物理研究所）
Jahn-Teller distortions and charge, orbital and magnetic orders in NaMn7O12
通过使用能带结构计算，我们证明了先前报道的[Nat. Materials { \bf 3}，48（2004）] NaMn $_7$ O $_{12}$的实验晶体和磁性结构彼此不一致。晶格的优化使我们能够预测一个新的晶体结构的低温相，这是定性不同于之前提出的。AFM-CE型的磁序稳定了结构，使Mn $^{3+}_B$ O $_6$八面体拉长而不压缩，使NaMn $_7$ O $_{12}$从反常的Jahn-Teller系统中消失。结果表明，即使在立方相中也存在轨道关联，而电荷有序仅出现在低温畸变相中。
Controlling structural distortion in the geometrically frustrated layered cobaltate YBaCo4O7+δ by Fe substitution and its role on magnetic correlations
Stretched exponential behavior in remanent lattice striction of a (La,Pr)$_{1.2}$Sr$_{1.8}$Mn$_{2}$O$_{7}$ bilayer manganite single crystal
本文研究了（La，Pr）$_{1.2}$ Sr $_{1.8}$ Mn $_{2}$ O $_{7}$单晶的弛豫磁致伸缩随时间的变化，以研究双层锰氧化物晶格畸变的慢动力学。双交换和Jahn-Teller型轨道-晶格相互作用之间的竞争导致所观察到的晶格轮廓遵循拉伸指数函数。这一发现表明，空间增长的本地晶格畸变加上电子$_{g}$ -电子轨道强烈相关的外观场诱导的CMR效应。
Valence-Bond Crystal, and Lattice Distortions in a Pyrochlore Antiferromagnet with Orbital Degeneracy
讨论了高阻挫烧绿石晶格上自旋为1/2的三重$t_{2g}$轨道简并磁性离子的基态性质，如B-尖晶石MgTi $_2$ O $_4$中的Ti $^{3+}$离子.在Hund耦合为零的情况下，我们构造了一个有效的自旋轨道哈密顿量，并通过构造几个精确的本征态研究了它的低能区。我们发现，轨道自由度调制的自旋交换能，释放烧绿石结构的无限自旋简并，并驱动系统到一个非磁性的自旋单重态流形。后者是自旋单重态二聚体的集合，然而，相对于二聚体取向高度简并。这种"定向“简并性随后被磁弹性相互作用提升，磁弹性相互作用通过在合适的方向上扭曲键并导致四元相来优化先前的能量增益。以这种方式，通过二聚体沿着围绕四角轴延伸的螺旋链的缩合形成价键晶体状态，如在MgTi $_2$ O $_4$中实际观察到的。在二聚相的轨道有序模式被预测为铁型沿螺旋和反铁型之间。最后，通过分析的考虑以及数值从头算模拟，我们预测一个可能的实验工具，通过共振X射线散射观察这样的轨道排序。
Combined single crystal polarized XAFS and XRD at high pressure: probing the interplay between lattice distortions and electronic order at multiple length scales in high $T_c$ cuprates
一些最奇特的材料特性来自于具有短相关长度（~10-500 μ m）的电子态，这表明局部结构对称性可能在它们的行为中起着相关的作用。在这里，我们讨论了在高压下结合使用偏振x射线吸收精细结构和x射线衍射作为一种强大的方法来调整和探测在多个长度尺度的结构和电子订单。除了解决一些与这些实验相关的技术挑战，我们说明了这种方法与铜氧化物La $_{1.875}$ Ba $_{0.125}$ CuO $_4$，其中电子顺序的压力的响应只能通过探测在相关的长度尺度的结构中获得的结果。
Magnetostrictive Neel ordering of the spin-5/2 ladder compound BaMn2O3: distortion-induced lifting of geometrical frustration
本文用热力学和衍射技术研究了BaMn $_2$ O $_3$的晶体结构和磁性。BaMn $_2$ O $_3$是$S = 5/2$自旋阶梯的实现，因为磁性相互作用沿着形成阶梯的腿和横档的180个$^\circ$ Mn-O-Mn键占主导地位。的磁化率的温度依赖性表现出良好定义的最大值为所有方向证明低维磁字符在BaMn $_2$ O $_3$。然而，磁化率和粉末中子衍射数据表明，BaMn $_2$ O $_3$在184 K时表现出向反铁磁有序的转变，尽管在正交高温相中最近邻的梯间耦合完全受挫。这种挫败感被伴随着磁性转变的非常强烈的单斜畸变所解除。
Structural studies on $A_2$ReCl$_6$ ($A$=K, Rb, Cs): absence of Jahn-Teller distortion
II. Physikalisches Institut, Universität zu Köln（科隆大学第二物理研究所）；Laboratory for Neutron Scattering and Imaging, PSI（瑞士保罗谢勒研究所中子散射与成像实验室）；Institut Laue-Langevin（朗之万研究所）；Institute of Geology and Mineralogy, Sect. Crystallography, University of Cologne（科隆大学地质与矿物学系晶体学部门）
Extensive infrared spectroscopic study of CuO: signatures of strong spin-phonon interaction and structural distortion
Optical properties of single-crystal monoclinic CuO in the range 70 - 6000 \cm were studied at temperatures from 7 to 300 K. Normal reflection spectra were obtained from the (001) and (010) crystal faces thus giving for the first time separate data for the $A_{u}$ and $B_{u}$ phonon modes excited in the purely transverse way (TO modes). Mode parameters, including polarizations of the $B_{u}$ modes not determined by the crystal symmetry, were extracted by the dispersion analysis of reflectivity curves as a function of temperature. Spectra of all the components of the optical conductivity tensor…
