In BaFe2As2, structural and magnetic planar defects begin to proliferate below the structural phase transition, affecting descriptions of magnetism and superconductivity. We study, using density-functional theory, the stability and magnetic properties of competing antiphase and domain boundaries, twins and isolated nanotwins (twin nuclei), and spin excitations proposed and/or observed. These nanoscale defects have a very low surface energy (22–210 m Jm−2), with twins favorable to the mesoscale. Defects exhibit smaller moments confined near their boundaries—making a uniform-moment picture inappropriate for long-range magnetic order in real samples. Nanotwins explain features in measured pair distribution functions so should be considered when analyzing scattering data. All these defects can be weakly mobile and/or can have fluctuations that lower assessed “ordered” moments from longer spatial and/or time averaging and should be considered directly.
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机译:在BaFe2As2中,结构和磁性平面缺陷在结构相变以下开始扩散,影响了对磁性和超导性的描述。我们使用密度泛函理论研究竞争性的反相和畴边界,孪晶和孤立的纳米孪晶(双核)以及提出和/或观察到的自旋激发的稳定性和磁性能。这些纳米级缺陷的表面能非常低(22–210 m Jm-2),并且孪晶对中尺度有利。缺陷表现出较小的力矩,限制在其边界附近,这使得均匀矩的图像不适合真实样本中的远距离磁阶。纳米孪晶解释了测得的对分布函数中的特征,因此在分析散射数据时应予以考虑。所有这些缺陷的移动性较弱,并且/或者可能存在波动,这些波动会导致较长的空间和/或时间平均评估的“有序”力矩降低,因此应直接考虑。
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