Antiferromagnetic ordering and structural phase transition inBa2Fe2As2with Sn incorporated from the growth flux

Abstract

Antiferromagnetic ordering and structural phase transition have been investigated via comprehensive neutron and x-ray diffraction on Sn-flux-grown ${\text{BaFe}}_{2}{\text{As}}_{2}$ single crystals, the $A\text{\ensuremath{-}}122$ family of FeAs-based high-${T}_{C}$ superconductor compounds. The incorporation of Sn in the lattice resulted to an average composition of ${\text{Ba}}_{0.95}{\text{Sn}}_{0.05}{\text{Fe}}_{2}{\text{As}}_{2}$. A tetragonal-to-orthorhombic structural phase transition and a three-dimensional long-range antiferromagnetic ordering of the iron magnetic moment, with a unique magnetic propagation wave vector $\mathbf{k}=(1,0,1)$ have been found to take place at $\ensuremath{\sim}90\text{ }\text{K}$. The magnetic moments of iron are aligned along the longer $\mathbf{a}$ axis in the low-temperature orthorhombic phase ($Fmmm$ with $\mathbf{b}<\mathbf{a}<\mathbf{c}$). Our results thus demonstrate that the magnetic structure of the Sn-flux-grown ${\text{BaFe}}_{2}{\text{As}}_{2}$ single crystal is the same as those in the polycrystalline samples and in other $A\text{\ensuremath{-}}122$ iron pnictides compounds. We argue that the Sn incorporation in the lattice is responsible for a smaller orthorhombic splitting and lower N\'eel temperature ${T}_{N}$ observed in the experiments.