Antiferromagnetic ordering and structural phase transition in Ba₂Fe₂As₂ with Sn incorporated from the growth flux

Antiferromagnetic ordering and structural phase transition have been investigated via comprehensive neutron and x-ray diffraction on Sn-flux-grown BaFe₂As₂ single crystals, the A-122 family of FeAs-based high-T_C superconductor compounds. The incorporation of Sn in the lattice resulted to an average composition of Ba_0.95Sn_0.05Fe₂As₂. 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 k=(1,0,1) have been found to take place at ∼90 K. The magnetic moments of iron are aligned along the longer a axis in the low-temperature orthorhombic phase (Fmmm with b<a<c). Our results thus demonstrate that the magnetic structure of the Sn-flux-grown BaFe₂As₂ single crystal is the same as those in the polycrystalline samples and in other A-122 iron pnictides compounds. We argue that the Sn incorporation in the lattice is responsible for a smaller orthorhombic splitting and lower Néel temperature T_N observed in the experiments.