The identification of the cross-plane electric transport mechanisms in different resistance states of metal-oxide sandwich structures is essential for gaining insights into the mechanisms of resistive switching (RS). Here, we present a systematic study of cross-plane electric transport properties of Pr 0.67 Ca 0.33 MnO 3 (PCMO) thin films sandwiched by precious Pt metal electrodes. We observe three different transport regimes: ohmic, nonlinear and RS. The nonlinear regime is associated with colossal magneto-resistance (CMR) and colossal electro-resistance (CER) effects. In contrast to RS, the CMR and CER are volatile resistance effects which persist only during application of strong magnetic or electric fields and they are restricted to low temperatures. At low current densities, the device resistance is dominated by small polaron hopping transport of the PCMO film. At higher electric current densities near the switching threshold, the interface resistance starts to dominate and remarkably also exhibits thermally activated transport properties. Our studies also shed light onto the interplay of colossal resistance effects and RS: at low temperatures, RS can be only induced by reduction of the PCMO resistivity through CMR and CER. This clearly demonstrates the key role of the current density for controlling the amplitude of non-volatile resistive changes. Conversely, the CMR can be used as a probe for the switching induced changes in disorder and correlations. At small switching amplitudes, we observe slight changes in polaron activation
The electrically induced persistent resistance change in perovskite Pr0.7Ca0.3MnO3 films sandwiched by metallic electrodes is analyzed with respect to noble electrode materials (Pt, Au, and Ag) and geometric arrangement by electrical transport measurements. Comparing switching behavior in symmetric and asymmetric electrode interfaces gives evidence for identifying the active, single interface in the switching process. The interaction of two opposing interfaces can lead to an observed switching polarity inversion in different current density regimes in the otherwise well defined bipolar behavior. The different noble metals exhibit a quite similar switching behavior, but a lower interfacial resistance seems to favor switching.
We report here on the presence of two different nonvolatile resistive switching mechanisms in Pt-Pr 0.67 Ca 0.33 MnO 3 -Pt sandwich structures based on pulsed electrical transport measurements. As a function of pulse length, amplitude and temperature, the devices show two different switching regimes. The first is positive switching (PS) where a high resistance state (HRS) evolves at positive bias at the top electrode in the voltage range of U ≈ 0.5-1.2 V and pulse lengths t p ≈ 10 −7 s. In addition, we observe a cross over to negative switching (NS) for U > 1 V and t p ≈ 10 −3 s. Here, the HRS evolves at negative bias applied at the top electrode. We present strong evidence that both switching mechanisms take place at the interface between Pr 0.67 Ca 0.33 MnO 3 and the top electrode. Based on finite element simulations of the temperature evolution during the electrical pulses, we show that the onset of Joule heating is characteristic of the PS regime, whereas drastic temperature increases of several hundred Kelvin evolve during NS. Based on the observed different timescales, pulse amplitudes and temperature dependences of PS and NS, respectively, we suggest that two different switching mechanisms are involved: a fast, short range exchange of oxygen at the interface with the metallic electrode for PS and a slower, long range redistribution of oxygen in the entire PCMO film for the NS.
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