We elucidate the magnetic phases and superconducting (SC) transition temperatures (T c ) in Sr 2 VFeAsO 3-δ (21113V), an iron-based superconductor with a thick-blocking layer fabricated from a perovskite-related transition metal oxide. At low temperatures (T < 37.1 K), 21113V exhibited a SC phase in the range 0.031 δ 0.145 and an antiferromagnetic (AFM) iron sublattice in the range 0.267 δ 0.664. Mixed-valent vanadium exhibited a dominant AFM phase in 0.031 c 0.088, and a partial ferrimagnetic (Ferri.) phase in the range 0.124 δ 0.664. The Ferri. phase was the most dominant at a δ value of 0.267, showing an AFM phase of Fe at T < 20 K. Increasing the spontaneous magnetic moments reduced the magnetic shielding volume fraction due to the SC phase. This result was attributed to the magnetic phase of vanadium, which dominates the superconductivity of Fe in 21113V. The T c -δ curve showed two maxima. The smaller and larger of T c maxima occurred at δ = 0.073 and δ = 0.145, respectively; the latter resides on the phase boundary between AFM and the partial Ferri. phases of vanadium. 21113V is a useful platform for verifing new mechanisms of T c enhancement in iron-based superconductors.
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