Clockwise vs Counter-Clockwise I-V Hysteresis of Point-Contact Metal-Tip/Pr_0.7 Ca_0.3MnO₃/Pt Devices

Metal-tip/Pr_0.7Ca_0.3MnO₃/Pt devices possess two types of I-V hysteresis: clockwise vs counter clockwise depending on the tip materials. The criteria for categorization of these two types of devices can be simply based on whether the Gibbs free energy of oxidation for the metal tip is lower or higher than that of PCMO, respectively. While the clockwise hysteresis can be attributed to electric field induced oxidation/reduction, the counter clockwise hysteresis can be explained by oxygen vacancy migration in an electrical field. Alternating-current conductance spectra also reveal distinct hopping barriers between these two categories of devices at high resistive states.