Hacisalihoglu M Y, Simonelli L, Marini C, Provino A, Martinelli A, Manfrinetti P, Putti M, Saini N L
Dipartimento di Fisica, Università di Roma 'La Sapienza', P. le Aldo Moro 2, 00185 Roma, Italy.
Department of Physics, Recep Tayyip Erdogan University, 53100 Rize, Turkey.
J Phys Condens Matter. 2020 Dec 16;33(9). doi: 10.1088/1361-648X/abcdb3.
The local structure of La(FeMn)AsO has been investigated using temperature dependent Fe K-edge extended x-ray absorption fine structure (EXAFS) measurements. The EXAFS data reveal distinct behavior of Fe-As and Fe-Fe atomic displacements with a clear boundary between⩽ 0.02 and> 0.02. The Fe-As bondlength shows a gradual thermal expansion while the Fe-Fe bond manifests a temperature dependent anomaly at ∼180 K for> 0.02. It is interesting to find characteristically different nature of Fe-As and Fe-Fe bondlengths shown by the temperature dependent mean square relative displacements. Indeed, the Fe-As bond, stiffer than that of the Fe-Fe, gets softer for⩽ 0.02 and hardly shows any change for> 0.02. On the other hand, Fe-Fe bond tends to be stiffer for⩽ 0.02 followed by a substantial softening for> 0.02. Such a distinction has been seen also in the As K-edge x-ray absorption near edge structure, probing local geometry around As atom together with the valence electronic structure. The results suggest that local atomic displacements by Mn substitution inducing increased iron local magnetic moment that should be the main reason for its dramatic effect in iron-based superconductors.
利用随温度变化的铁 K 边扩展 X 射线吸收精细结构（EXAFS）测量研究了 La(FeMn)AsO 的局部结构。EXAFS 数据揭示了 Fe-As 和 Fe-Fe 原子位移的不同行为，在⩽0.02 和>0.02 之间有明显界限。Fe-As 键长呈现出逐渐的热膨胀，而对于>0.02，Fe-Fe 键在约 180 K 时表现出与温度相关的异常。有趣的是，由随温度变化的均方相对位移所显示的 Fe-As 和 Fe-Fe 键长具有特征性的不同性质。实际上，比 Fe-Fe 键更硬的 Fe-As 键，对于⩽0.02 会变软，而对于>0.02 几乎没有任何变化。另一方面，Fe-Fe 键对于⩽0.02 倾向于变硬，随后对于>0.02 会大幅变软。在 As K 边 X 射线吸收近边结构中也观察到了这种差异，该结构探测了 As 原子周围的局部几何结构以及价电子结构。结果表明，Mn 替代引起的局部原子位移导致铁的局部磁矩增加，这应该是其在铁基超导体中产生显著效应的主要原因。
