Geometric magnetic frustration in the hexagonal perovskite (La,Sr)4- zRuO7+δ
Geometric magnetic frustration in the hexagonal perovskite (La,Sr)4- zRuO7+δ
复制标题
六方钙钛矿 (La,Sr)4- zRuO7+δ 中的几何磁挫败
DOI：
10.1103/physrevb.75.144414
复制
发表时间：
2007
影响因子：
3.7
通讯作者：
T. Götzfried
中科院分区：
文献类型：
--
作者：
S. Ebbinghaus;E. Scheidt;T. Götzfried
六方钙钛矿 $(\mathrm{La},\mathrm{Sr}{)}_{4\ensuremath{-}z}{\mathrm{RuO}}_{7+\ensuremath{\delta}}$ 由于顺磁性 ${\mathrm{Ru}}^{5+}$ 离子的几何排列而表现出强烈的磁挫败性，形成边缘共享的细长四面体网络。在这种磁性亚晶格中，挫败可能仅限于晶体$ab$平面（其中钌离子形成三角形晶格），也可能涉及整个四面体。通过浮区法生长 $(\mathrm{La},\mathrm{Sr}{)}_{4\ensuremath{-}z}{\mathrm{RuO}}_{7+\ensuremath{\delta}}$ 晶体，并测量其相对于晶轴的磁性能。仅在平行于 $ab$ 平面的外部磁场中检测到磁序，而对于 $\mathbf{B}\ensuremath{\Vert}c$，样品没有显示出向下至 $2\phantom{\rule{0.3em}{0ex}}\mathrm{K}$ 的磁转变。热容测量显示，磁熵对应于 1/2 的自旋，该值远小于 ${\mathrm{Ru}}^{5+}$ 离子的 $({t}_{2g}{)}^{3}$ 配置的预期 $S=3∕2$。从对称性考虑，我们得出结论，只有对应于不可约表示 ${A}_{1g}$ 的轨道才能介导磁矩之间的协作相互作用，从而产生轨道有序状态。
The hexagonal perovskite $(\mathrm{La},\mathrm{Sr}{)}_{4\ensuremath{-}z}{\mathrm{RuO}}_{7+\ensuremath{\delta}}$ exhibits a strong magnetic frustration due to the geometric arrangement of the paramagnetic ${\mathrm{Ru}}^{5+}$ ions, which form a network of edge-sharing elongated tetrahedra. In this magnetic sublattice, frustration may either be restricted to the crystallographic $ab$ plane, in which the ruthenium ions form a triangle lattice, or concern the entire tetrahedra. Crystals of $(\mathrm{La},\mathrm{Sr}{)}_{4\ensuremath{-}z}{\mathrm{RuO}}_{7+\ensuremath{\delta}}$ were grown by the floating zone method, and their magnetic properties were measured with respect to the crystallographic axes. Magnetic ordering was only detected for the external magnetic field parallel to the $ab$ plane, while for $\mathbf{B}\ensuremath{\Vert}c$ the samples showed no magnetic transition down to $2\phantom{\rule{0.3em}{0ex}}\mathrm{K}$. Heat capacity measurements revealed a magnetic entropy corresponding to a spin of 1/2, a value much smaller than the $S=3∕2$ expected for the $({t}_{2g}{)}^{3}$ configuration of ${\mathrm{Ru}}^{5+}$ ions. From symmetry considerations, we conclude that only the orbitals corresponding to the irreducible representation ${A}_{1g}$ mediate the cooperative interaction between the magnetic moments, giving rise to an orbitally ordered state.