Electrical transport effects in YBCO/LSMO bilayer junctions

Highlights: • Electrical transport across HTS YBCO/FM LSMO junctions is studied by 4-probe method. • Measured junction resistance R_j at T < T_C is lower than the interface resistance R_if. • It is shown how to evaluate right interface resistance R_if from measurements of R_j. • I-V characteristic can change sign in dependence on current I₀ flowing across junction. • The effect is quantitatively described using a model, proposed in the paper. - Abstract: The electrical transport effects in interfaces of high T_C superconducting and ferromagnetic thin film bilayer structures (YBa₂Cu₃O_x/La_0.67Sr_0.33MnO₃ 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 R_j, measured by a standard four probe method at T < T_C, can be significantly lower (even a few orders) than the real interface resistance R_if because of which a wrong interpretation of the last may occur. We show how to evaluate the right interface resistance and the real R_if was determined from the measurement of R_J 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 R_J at T > T_C were discussed as well.