We show that for hybrid oxide-metal trilayer junctions of ${\mathrm{Co}}_{0.8}{\mathrm{Fe}}_{0.2}-{\mathrm{SrTiO}}_3-{\mathrm{La}}_{0.67}{\mathrm{Sr}}_{0.33}{\mathrm{MnO}}_3$ and $\mathrm{Fe}-{\mathrm{SrTiO}}_3-{\mathrm{La}}_{0.67}{\mathrm{Sr}}_{0.33}{\mathrm{MnO}}_3,$ the sign and field dependence of junction magnetoresistance are sensitive to the junction interface condition. Both positive and negative magnetoresistance can be obtained in either system, depending on the state of the junction interface. For high biases above 0.5 V, junction resistance shows time-dependent creep. The magnitude and direction of the creep depend on the magnitude and direction of the applied bias, indicating reversible structural modification of the junction interface. For these junctions, the interface chemistry, rather than fundamental band structures of the electrode materials, appears responsible for the observed sign-change of junction magnetoresistance.

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