Magnetic structure of CaBaCo 4 O 7 : Lifting of geometrical frustration towards ferrimagnetism
Magnetic structure of CaBaCo 4 O 7 : Lifting of geometrical frustration towards ferrimagnetism
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DOI：
10.1103/physrevb.81.094417
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发表时间：
2010-02
影响因子：
3.7
通讯作者：
V. Caignaert;V. Pralong;V. Hardy;C. Ritter;B. Raveau
中科院分区：
文献类型：
--
作者：
V. Caignaert;V. Pralong;V. Hardy;C. Ritter;B. Raveau
${\Text{CaBaCo}}_{4}{\Text{O}}_{7}$代表一类亚铁磁体，其结构仅由${\Text{CoO}}_{4}$四面体构成，类似于`114‘系列的其他成员${\Text{LnBaCo}}_{4}{\Text{O}}_{7}$，形成Kagom层和三角形层的交替堆叠。中子粉末衍射表明，该化合物在“114”系列中表现出最大的变形，表现为kagom层的强烈屈曲。与所有其他成员不同，它显示出电荷顺序，${\Text{Co}}^{2+}$位于两个位置(CO_2，CO_3)，而“混合价”钴``${\text{Co}}^{3+}/{\text{Co}}^{2+}\underset{}{\text{L}}$‘’位于另外两个位置(CO_1，Co_4)。这种钴铁矿在4K时独特的亚铁磁性结构可以描述为垂直于Kagom e层的亚铁磁性三链(Co1，Co2，Co3)的组合，在层内铁磁耦合，并与第四种钴物种Co4反铁磁耦合。尽管钴晶格呈三角形拓扑，但几何挫折向亚铁磁性的解除是由于与其他${\Text{LnBaCo}}_{4}{\Text{O}}_{7}$氧化物相比，结构扭曲很大，电荷有序现象和钴的价态很高。
${\text{CaBaCo}}_{4}{\text{O}}_{7}$ represents a class of ferrimagnets whose structure is built up of ${\text{CoO}}_{4}$ tetrahedra only, similarly to other members ${\text{LnBaCo}}_{4}{\text{O}}_{7}$ of the ``114'' series, forming an alternate stacking of kagom\'e and triangular layers. Neutron powder diffraction reveals, that this compound exhibits the largest distortion within the ``114'' series, characterized by a strong buckling of the kagom\'e layers. Differently from all other members it shows charge ordering, with ${\text{Co}}^{2+}$ sitting on two sites (Co2, Co3) and ``mixed valent'' cobalt ``${\text{Co}}^{3+}/{\text{Co}}^{2+}\underset{}{\text{L}}$'' sitting on two other sites (Co1, Co4). The unique ferrimagnetic structure of this cobaltite at 4 K can be described as the assemblage of ferrimagnetic triple chains (Co1 Co2 Co3) running perpendicular to the kagom\'e layers, ferromagnetically coupled within the layers, and antiferromagnetically coupled with a fourth cobalt species Co4. The lifting of the geometrical frustration toward ferrimagnetism, which appears in spite of the triangular topology of the cobalt lattice, is explained by the very large structural distortion, charge ordering phenomena and large cobalt valence compared to other ${\text{LnBaCo}}_{4}{\text{O}}_{7}$ oxides.