Magnetic-Electronic, Conductivity, and Structural Pressure Studies of Sr₂FeO₄ and Sr₃Fe₂O₇

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Sr₂FeO₄ and Sr₃Fe₂O₇ have been investigated by resistance-temperature, ⁵⁷Fe-Mössbauer magnetic and x-ray diffraction studies up to ∼30 GPa. Magnetic moments in Sr₂FeO₄ remain intact across the conductivity transition to a metallic state at ∼17 GPa. The complex spiral-type magnetic structure at low pressure changes to collinear in the metallic state. In Sr₃Fe₂O₇ the original disproportionated state and associated magnetic-electronic structure first exhibits a change at ∼12-15 GPa, and only a single valence state is discernible at P ≥ 21 GPa. A very narrow gapped state prevalent at ∼10 GPa undergoes a sluggish transition to incipient metallic behavior at ∼28 GPa. X-ray data suggest that the magnetic-electronic and conductivity transitions in both compounds are not driven by symmetry-lowering structural transitions.