Symmetry of reentrant tetragonal phase in Ba 1 -x Na x Fe 2 As 2 : Magnetic versus orbital ordering mechanism
Symmetry of reentrant tetragonal phase in Ba 1 -x Na x Fe 2 As 2 : Magnetic versus orbital ordering mechanism
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DOI：
10.1103/physrevb.90.174511
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发表时间：
2014-09
影响因子：
3.7
通讯作者：
D. Khalyavin;S. Lovesey;P. Manuel;F. Kruger;S. Rosenkranz;J. M. Allred;O. Chmaissem;R. Osborn
中科院分区：
文献类型：
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作者：
D. Khalyavin;S. Lovesey;P. Manuel;F. Kruger;S. Rosenkranz;J. M. Allred;O. Chmaissem;R. Osborn
采用朗道相变理论中的对称性分析方法，讨论了Ba 1 − xAxFe 2As 2（A = K，Na）材料的磁结构相变的磁驱动机制和轨道驱动机制.这两种机制都预言了在相图的大部分区域中观察到的磁相和磁相具有相同的正交空间群对称性，但它们预言了在Ba 1 − xNaxFe 2As 2（x <$0.24 -0.28）中新发现的重入四重相具有不同的四重空间群对称性。在磁性的情况下，磁性有序与沿c轴沿着的力矩，实验发现，不允许任何类型的轨道顺序，但在轨道的情况下，我们已经确定了两种可能的轨道模式，由P4/mnc 1 '和I4221'空间群指定，这不需要相对于母I4/mmm 1 '对称性的原子位移，因此，在传统的衍射实验中是无法区分的。我们表明，这三种可能的空间群，但是，不同的共振X射线布拉格衍射模式创建的Templeton和Templeton散射。这提供了一种区分磁模型和轨道模型的实验方法。
Magnetostructural phase transitions in Ba1−xAxFe2As2 (A = K, Na) materials are discussed for both magnetically and orbitally driven mechanisms, using a symmetry analysis formulated within the Landau theory of phase transitions. Both mechanisms predict identical orthorhombic space-group symmetries for the nematic and magnetic phases observed over much of the phase diagram, but they predict different tetragonal space-group symmetries for the newly discovered reentrant tetragonal phase in Ba1−xNaxFe2As2 (x∼0.24–0.28). In a magnetic scenario, magnetic order with moments along the c axis, as found experimentally, does not allow any type of orbital order, but in an orbital scenario, we have determined two possible orbital patterns, specified by P4/mnc1′ and I4221′ space groups, which do not require atomic displacements relative to the parent I4/mmm1′ symmetry and, in consequence, are indistinguishable in conventional diffraction experiments. We demonstrate that the three possible space groups are, however, distinct in resonant x-ray Bragg diffraction patterns created by Templeton & Templeton scattering. This provides an experimental method of distinguishing between magnetic and orbital models.