Electric field control of phase transition and tunable resistive switching in SrFeO2.5.

SrFeOx (SFOx) compound exhibits 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 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) film 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 SrFeO3-δ (SFO3-δ) layer shows 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-δ. Whereas the suppression of both magnetic and exchange coupling signals for 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 (RS) parameters, such as set, reset and high/low-resistance ratio in SFO2.5-based resistive random access memory devices.