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

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 ~1215 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, [high pressure, Mossbauer spectroscopy, x-ray diffraction, semiconductor-metal transition, disproportionation].