We report ${}^{75}$As and ${}^{51}$V nuclear magnetic resonance (NMR) measurements on the iron-based superconductor ${\text{Sr}}_2$${\text{VFeAsO}}_3$ with alternating stacks structure. We find that the ${}^{75}$As nuclear spin-spin relaxation rate ($1/T_2$) shows a pronounced peak at $T_N$ = 165 K, below which the resonance peak shifts to a higher frequency due to the onset of an internal magnetic field. The ${}^{51}$V spectrum does not shift, but is broadened below $T_N$. We conclude that the Fe electrons order antiferromagnetically below $T_N$ with a magnetic moment $m_{Fe}$ $\sim$ 0.4 ${\mu }_B$. Application of external pressure up to 2.4 GPa reduces $T_N$ at a rate of $-$40 K/GPa, and enhances the superconducting transition temperature $T_c$ at a rate of 2 K/GPa. The pressure-temperature phase diagram for ${\text{Sr}}_2$${\text{VFeAsO}}_3$ shows that superconductivity coexists with antiferromagnetism over a wide pressure range with an unprecedented high $T_c$ up to 36.5 K.

• Received 19 March 2014
• Revised 24 April 2014

DOI:https://doi.org/10.1103/PhysRevB.89.184506