Electric Field Control of Phase Transition and Tunable Resistive Switching in SrFeO2.5

SrFeOx (SFOx) compounds exhibit ionic conduction and oxygen related phase transformation, having potential applications in solid oxide fuel cells, smart windows, and memristive devices. The phase transformation in SFOx typically requires a thermal annealing process under various pressure conditions, hindering their practical applications. Here, we have achieved a reversible phase transition from brownmillerite (BM) to perovskite (PV) in SrFeO2.5 (SFO2.5) films through ionic liquid (IL) gating. The real-time phase transformation is imaged using in situ high resolution transmission electron microscopy. The magnetic transition in SFO2.5 is identified by fabricating an assisted La0.7Sr0.3MnO3 (LSMO) bottom layer. The IL-gating-converted PV phase of a SrFeO3-delta (SFO3-delta) layer shows a ferromagnetic-like behavior but applies a huge pinning effect on LSMO magnetic moments, which consequently leads to a prominent exchange bias phenomenon, suggesting an uncompensated helical magnetic structure of SFO3-delta. On the other hand, the suppression of both magnetic and exchange coupling signals for a BM-phased SFO2.5 layer elucidates its fully compensated G-type antiferromagnetic nature. We also demonstrated that the phase transition by IL gating is an effective pathway to tune the resistive switching parameters, such as set, reset, and high/low-resistance ratio in SFO2.5-based resistive random-access memory devices.