Transport across conducting ferromagnetic oxide/metal interfaces

We have investigated transport properties across interfaces between the conducting ferromagnetic oxides ${\mathrm{SrRuO}}_{\mathrm{3}},$ ${\mathrm{La}}_{\mathrm{0.5}}{\mathrm{Sr}}_{\mathrm{0.5}}{\mathrm{CoO}}_{\mathrm{3}},$ ${\mathrm{La}}_{\mathrm{0.67}}{\mathrm{Sr}}_{\mathrm{0.33}}{\mathrm{MnO}}_{\mathrm{3}},$ and the metals Nb, Al, Pd, and Au. The interface resistances range from smaller than ${10}^{\text{−8}}$ to ${10}^2\mathrm{\hspace{0.17em}\Omega \hspace{0.17em}}{\mathrm{cm}}^{\mathrm{2}},$ depending on the choice of ferromagnetic oxide and metal. The three conducting metal oxides exhibit distinctly different behavior in their interface resistances with metals, which we believe is due to different processes taking place at the interface. By making the metals superconducting at 4.2 K, by proximity effect with a capping Nb layer, we show that the dominant transport mechanism through the resistive interface seems to be elastic tunneling. In the case of ${\mathrm{La}}_{\mathrm{0.67}}{\mathrm{Sr}}_{\mathrm{0.33}}{\mathrm{MnO}}_{\mathrm{3}}\mathrm{/Al}$ interfaces, we found a way to control the magnitude of the tunneling resistance by adding a very thin Pd layer.