Electronic Transport and Resistive Switching Properties in Topotactic SrFe1-x CoxO2.5 Devices

SrFe1-xCoxO2.5 (SFCO) brownmillerite is an intriguing transition metal oxide compound that exhibits a redox-driven topotactic phase transition from the insulating antiferromagnetic state to the conductive perovskite SrFe1-xCoxO3 ferromagnetic metallic state with a relatively high Curie temperature (340 K). However, its resistive switching properties and electronic transport have seldom been investigated. Herein, we investigate the resistive switching characteristics of epitaxially grown heterostructures of SFCO/SrRuO3/SrTiO3 (001). The Co substitution (x) in SFCO films was chosen as follows: x = 0.66, with a high Curie temperature (similar to 340 K), and x = 0.33, with a reduced Curie temperature (similar to 310 K). Very stable, nonvolatile, bipolar resistive switching characteristics were observed for both SFCO variants, while the highest Co-doped film demonstrated a relatively large ON/OFF ratio and smaller set current compared to the lowest Co-doped film. The highest Co-doped SFCO device showed multifilamentary resistive switching properties due to the random formation of conductive filaments (CFs). During voltage sweeps of SFCO devices, two charge carrier tunneling mechanisms were observed: direct tunneling at the forward bias high-resistance state (HRS) and Fowler-Nordheim-type tunneling at the reverse bias HRS during the higher reverse electric field. Additionally, nanoscopic investigation of CF formation on the SFCO film surface via conductive atomic force microscopy revealed localized multifilamentary formation that validated CF-mediated resistive switching in SFCO films.