Electrical transport effects in YBCO/LSMO bilayer junctions

The electrical transport effects in interfaces of high TC superconducting and ferromagnetic thin film bilayer structures (YBa2Cu3Ox/La0.67Sr0.33MnO3 junctions with areas of ∼0.2 × 10−4 cm2 and ∼1.21 × 10−4 cm2) were investigated in view of the importance of such structures for oxide electronics and spintronics applications. In some structures the junction resistance Rj, measured by a standard four probe method at T < TC, can be significantly lower (even a few orders) than the real interface resistance Rif because of which a wrong interpretation of the last may occur. We show how to evaluate the right interface resistance and the real Rif was determined from the measurement of RJ for the above two junctions. An unordinary effect - a “change” of the sign of the I-V characteristics in dependence on the current I0 flowing across the bilayer junction was observed in our experiments. We explained the essence of the effect and quantitatively described the effect using a model, proposed in the paper. The conditions for observation of a “negative” value of RJ at T > TC were discussed as well.