Spin and lattice structures of single-crystallineSrFe2As2

Abstract

We use neutron scattering to study the spin and lattice structure of single-crystal ${\text{SrFe}}_{2}{\text{As}}_{2}$, the parent compound of the FeAs-based superconductor $(\text{Sr},\text{K}){\text{Fe}}_{2}{\text{As}}_{2}$. We find that ${\text{SrFe}}_{2}{\text{As}}_{2}$ exhibits an abrupt structural phase transition at 220 K, where the structure changes from tetragonal with lattice parameters $c>a=b$ to orthorhombic with $c>a>b$. At almost the same temperature, Fe spins develop a collinear antiferromagnetic structure along the orthorhombic $a$ axis with spin direction parallel to this $a$ axis. These results are consistent with earlier work on the $R\text{FeAsO}$ ($R=\text{rare}$ earth) families of materials and on ${\text{BaFe}}_{2}{\text{As}}_{2}$, and therefore suggest that static antiferromagnetic order is ubiquitous for the parent compounds of these FeAs-based high-transition temperature superconductors.