用单晶中子衍射研究三方晶系SrMn $_{2}$ As $_{2}$的共线反铁磁性
Collinear antiferromagnetism in trigonal SrMn$_{2}$As$_{2}$ revealed by single-crystal neutron diffraction
摘要：
铁磷属元素化物及其相关材料一直是理解磁性和超导性之间复杂相互作用的热门研究课题。在这里，我们报告的磁性结构的SrMn $_{2}$作为$_{2}$，结晶在一个三角结构（$P\bar{3}m1$）和经历反铁磁（AFM）转变在$T_{\textrm c}$ $= 118(2)$ K。磁化率在温度$T \le T_{\textrm N}$和$\textbf{H}\parallel \textbf{c}$下几乎保持恒定，而在温度$\textbf{H}\parallel \textbf{ab}$下磁化率显著降低。这表明有序Mn矩位于$\textbf{ab}$ -平面中，而不是如在四元BaMn $_{2}$ As $_{2}$中那样沿$\textbf{c}$ -轴排列。SrMn $_{2}$ As $_{2}$的单晶中子衍射测量表明，Mn矩在共线的Néel AFM相中有序排列，$180^\circ$ AFM在一个矩和所有最近邻矩之间排列，并且垂直于它。此外，准二维AFM有序在SrMn $_{2}$ As $_{2}$中表现出来，从有序参数的温度依赖性可以看出。
英文摘要：
Fe pnictides and related materials have been a topic of intense research for understanding the complex interplay between magnetism and superconductivity. Here we report on the magnetic structure of SrMn$_{2}$As$_{2}$ that crystallizes in a trigonal structure ($P\bar{3}m1$) and undergoes an antiferromagnetic (AFM) transition at $T_{\textrm c}$ $= 118(2)$ K. The magnetic susceptibility remains nearly constant at temperatures $T \le T_{\textrm N}$ with $\textbf{H}\parallel \textbf{c}$ whereas it decreases significantly with $\textbf{H}\parallel \textbf{ab}$. This shows that the ordered Mn moments lie in the $\textbf{ab}$-plane instead of aligning along the $\textbf{c}$-axis as in tetragonal BaMn$_{2}$As$_{2}$. Single-crystal neutron diffraction measurements on SrMn$_{2}$As$_{2}$ demonstrate that the Mn moments are ordered in a collinear Néel AFM phase with $180^\circ$ AFM alignment between a moment and all nearest neighbor moments in the basal plane and also perpendicular to it. Moreover, quasi-two-dimensional AFM order is manifested in SrMn$_{2}$As$_{2}$ as evident from the temperature dependence of the order parameter.
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