${\mathrm{Co}}_4{\mathrm{Ta}}_2{\mathrm{O}}_9$ exhibits a three-dimensional magnetic lattice based on the buckled honeycomb motif. It shows unusual magnetoelectric effects, including the sign change and nonlinearity. These effects cannot be understood without the detailed knowledge of the magnetic structure. Herein, we report neutron diffraction and direction-dependent magnetic susceptibility measurements on ${\mathrm{Co}}_4{\mathrm{Ta}}_2{\mathrm{O}}_9$ single crystals. Below 20.3 K, we find a long-range antiferromagnetic order in the alternating buckled and flat honeycomb layers of ${\mathrm{Co}}^{2+}$ ions stacked along the $\mathit{c}$ axis. Within experimental accuracy, the magnetic moments lie in the $\mathit{ab}$ plane. They form a canted antiferromagnetic structure with a tilt angle of $\sim {14}^{\circ }$ at 15 K in the buckled layers, while the magnetic moments in each flat layer are collinear. This is directly evidenced by a finite (0, 0, 3) magnetic Bragg peak intensity, which would be absent in the collinear magnetic order. The magnetic space group is $C{2}^{\prime }/c$. It is different from the previously reported $C2/c^{\prime }$ group, also found in the isostructural ${\mathrm{Co}}_4{\mathrm{Nb}}_2{\mathrm{O}}_9$. The revised magnetic structure successfully explains the major features of the magnetoelectric tensor of ${\mathrm{Co}}_4{\mathrm{Ta}}_2{\mathrm{O}}_9$ within the framework of the spin-flop model.

中文翻译：

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单晶中子衍射测定Co4Ta2O9磁电弯曲蜂窝晶格中的非共线反铁磁序

${\mathrm{有限公司}}_4{钽}_2{\mathrm{Ø}}_9$展示了基于弯曲蜂窝状图案的三维磁性晶格。它显示出异常的磁电效应，包括符号变化和非线性。没有磁性结构的详细知识，就无法理解这些效果。在这里，我们报告中子衍射和方向相关的磁化率测量${\mathrm{有限公司}}_4{钽}_2{\mathrm{Ø}}_9$单晶。低于20.3 K，我们在交替的弯曲和扁平蜂窝层中发现了远距离反铁磁序${\mathrm{有限公司}}^{2+}$ 离子沿着 $\mathit{C}$轴。在实验精度范围内，磁矩位于$\mathit{b}$飞机。它们形成倾斜的反铁磁结构，倾斜角为$〜{14}^{\circ }$弯曲层中的磁矩为15 K，而每个平坦层中的磁矩是共线的。这由有限的（0，0，3）磁布拉格峰强度直接证明，在共线磁阶中将不存在。磁空间群是$C{2}^{\prime }/C$。它不同于以前报道的$C2/C^{\prime }$ 组，也存在于同构中 ${\mathrm{有限公司}}_4{铌}_2{\mathrm{Ø}}_9$。修改后的磁结构成功地解释了磁张量的主要特征${\mathrm{有限公司}}_4{钽}_2{\mathrm{Ø}}_9$ 在旋转触发器模型的框架内。