Magnetism and superconductivity in Sr2 VFeAsO3 revealed by 75 As- and 51 V-NMR under elevated pressures

We report 75As and 51V nuclear magnetic resonance (NMR) measurements on the iron-based superconductor Sr2VFeAsO3 with alternating stacks structure. We find that the 75As nuclear spin-spin relaxation rate (1/T2) shows a pronounced peak at TN = 165 K, below which the resonance peak shifts to a higher frequency due to the onset of an internal magnetic field. The 51V spectrum does not shift, but is broadened below TN. We conclude that the Fe electrons order antiferromagnetically below TN with a magnetic moment mFe ∼ 0.4 μB. Application of external pressure up to 2.4 GPa reduces TN at a rate of -40 K/GPa, and enhances the superconducting transition temperature Tc at a rate of 2 K/GPa. The pressure-temperature phase diagram for Sr2VFeAsO3 shows that superconductivity coexists with antiferromagnetism over a wide pressure range with an unprecedented high Tc up to 36.5 K.