Self doping effect and successive magnetic transitions in superconducting Sr$_2$VFeAsO$_3$

TL;DR

This study investigates the self doping and magnetic transitions in the superconducting Sr$_2$VFeAsO$_3$, revealing electron transfer from V ions and successive magnetic orderings within the VO$_2$ layers.

Contribution

It demonstrates self doping via electron transfer from V ions and identifies two successive magnetic transitions in Sr$_2$VFeAsO$_3$, a novel finding in this superconductor.

Findings

Self doping occurs through electron transfer from V$^{3+}$ ions.

Successive magnetic transitions at 150 K and 55 K.

Mixed valence states of V$^{3+}$ and V$^{4+}$ are involved.

Abstract

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