Pressure-Induced Structural, Magnetic and Transport Transitions in the Two-Legged Ladder Sr$_{3}$Fe$_{2}$O$_{5}$

The layered compound SrFeO$_{2}$ with an FeO$_{4}$ square-planar motif exhibits an unprecedented pressure-induced spin state transition ($S$ = 2 to 1), together with an insulator-to-metal (I-M) and an antiferromagnetic-to-ferromagnetic (AFM-FM) transition. In this study, we have studied the pressure effect on the structural, magnetic and transport properties of the structurally related two-legged spin ladder Sr$_{3}$Fe$_{2}$O$_{5}$. When pressure was applied, this material first exhibited a structural transition from \textit{Immm} to \textit{Ammm }at $P_{s}$ = 30 $\pm $ 2 GPa. This transition involves a phase shift of the ladder blocks from (1/2,1/2,1/2) to (0,1/2,1/2), by which a rock-salt type SrO block with a seven-fold coordination around Sr changes into a CsCl-type block with eight-fold coordination, allowing a significant reduction of volume. However, the $S$ = 2 antiferromagnetic state stays the same. Next, a spin state transition from $S$ = 2 to $S$ = 1, along with an AFM-FM transition was observed at $P_{c}$ = 34 $\pm $ 2 GPa, similar to that of SrFeO$_{2}$. A sign of an I-M transition was also observed at pressure around $P_{c}$.