We have studied a quinary Fe-based superconductor ${\text{Sr}}_2{\text{VFeAsO}}_3$ by the measurements of x-ray diffraction, x-ray absorption, Mössbauer spectrum, resistivity, magnetization, and specific heat. This apparently undoped oxyarsenide is shown to be self-doped via electron transfer from the ${\text{V}}^{3+}$ ions. We observed successive magnetic transitions within the ${\text{VO}}_2$ layers: an antiferromagnetic transition at 150 K followed by a weak ferromagnetic transition at 55 K. The spin orderings within the ${\text{VO}}_2$ planes are discussed based on mixed valence of ${\text{V}}^{3+}$ and ${\text{V}}^{4+}$.

• Received 1 September 2010

DOI:https://doi.org/10.1103/PhysRevB.82.104518