Understanding frequency-dependent hysteresis-like current–voltage characteristics in AC-driven ferromagnetic La0.7Sr0.3MnO3 perovskite oxide across broad temperature range

Alternating–current (AC) poling frequently triggers abnormal physical phenomena of materials. For ferroelectric materials, it will probably make further improvement on their polarization properties, compared to conventional direct-current (DC) poling. Temperature- and frequency- dependence of AC and DC conductivities can provide valuable insights into the distinctive carrier transport mechanisms in perovskites. Therefore, it is crucial to conduct comprehensive investigations into AC-driven perovskite manganites across a broad temperature range (BTR). In this study, La0.7Sr0.3MnO3 (LSMO) thin films were successfully synthesized on Nb-doped SrTiO3 (Nb-STO) substrate by using pulsed laser deposition technology. A primary focus was placed on examining both DC and AC electrical properties of LSMO films over BTR (70–300 K). Notably, AC current–voltage (I–V) characteristics of LSMO/Nb-STO heterostructure exhibited an unprecedented frequency-dependent hysteresis-like loop with the switchover of voltage sweeping direction. So this phenomenon, previously unreported, was thoroughly analyzed based on the “patch” model. Furthermore, the deviation of the AC I–V characteristics from classical thermionic emission theory was investigated. This deviation is attributed to the combined influence of several critical factors associated with ferromagnetic perovskite manganites, including depletion layer dimensions, Schottky barrier height inhomogeneity, and temperature-dependent carrier scattering mechanisms. The results reveal that a decrease in temperature suppresses interfacial scattering, thereby enhancing electron transport within the LSMO heterostructure. Additionally, AC poling was found to directly influence the relative scale of LSMO/Nb-STO depletion region compared to the one with “patch” distribution. This, in turn, governs the charge transfer pathways across the hetero-interface and determines the complex temperature-dependent ideality factor of the LSMO/Nb-STO junction.