“114”钴矿中磁滞“磁-输运-结构”转变：尺寸失配效应
Hysteretic "Magnetic-Transport-Structural" Transition in "114" Cobaltites: Size Mismatch Effect
摘要：
本文用磁性、输运和差示扫描量热法研究了三个系列的“114”钴酸盐Y1-xYbxBaCo_4 O_7、Y1-xCaxBaCo_4 O_7和Yb_1-xCaxBaCo_4 O_7的三重“磁输运结构”转变随温度的变化。首次在三角晶格中显示了由于Ln位上的阳离子无序引起的尺寸失配σ2对这种转变的影响。我们发现，增加<rLn>具有显着增加TS的效果，而在Ln位置的尺寸失配σ2大幅降低TS。此外，在Ln位点的阳离子失配通过将未掺杂样品中所见的尖锐的一阶跃转变为一阶跃和二阶跃的混合来修改滞后跃变的性质。这些结果是根据高温形式相对于低温斜方晶形式（空间群：Pbn 21）表现出六方密堆积结构（空间群：P63 mc）的特殊性质进行讨论的，后者对应于前者的变形由于kagomé层的褶皱。
英文摘要：
The triple "magnetic-transport-structural" transition versus temperature in three series of "114" cobaltites - Y1-xYbxBaCo4O7, Y1-xCaxBaCo4O7 and Yb1-xCaxBaCo4O7 - has been studied using magnetic, transport and differential scanning calorimetric measurements. The effect of the size mismatch σ2, due to cationic disordering at the Ln sites upon such a transition is shown for the first time in a triangular lattice. We show that increasing <rLn> has an effect of increasing TS dramatically, while the size mismatch σ2 at the Ln sites decreases TS substantially. Moreover, the cationic mismatch at the Ln sites modifies the nature of the hysteretic transition by turning the sharp first order transition seen in the undoped samples into an intermix of first and second order transitions. These results are discussed on the basis of the particular nature of the high temperature form which exhibits a hexagonal close packed structure (space group: P63mc) with respect to the low temperature orthorhombic form (space group: Pbn21), the latter corresponding to a distortion of the former due to a puckering of the kagomé layers.
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