Transport and spectroscopic properties of superconductor - ferromagnet - superconductor junctions of $La_{1.9}Sr_{0.1}CuO_4$ - $La_{0.67}Ca_{0.33}MnO_3$ - $La_{1.9}Sr_{0.1}CuO_4$

摘要

Transport and Conductance spectra measurements of ramp-type junctions made ofcuprate superconducting $La_{1.9}Sr_{0.1}CuO_4$ electrodes and a manganiteferromagnetic $La_{0.67}Ca_{0.33}MnO_3$ barrier are reported. At lowtemperatures below $T_c$, the conductance spectra show Andreev-like broad peakssuperposed on a tunneling-like background, and sometimes also sub-gap Andreevresonances. The energy gap values $\Delta$ found from fits of the data rangedmostly between 7-10 mV. As usual, the gap features were suppressed undermagnetic fields but revealed the tunneling-like conductance background. Afterfield cycling to 5 or 6 T and back to 0 T, the conductance spectra were alwayshigher than under zero field cooling, reflecting the negative magnetoresistanceof the manganite barrier. A signature of superparamagnetism was found in theconductance spectra of junctions with a 12 nm thick LCMO barrier. Observedcritical currents with barrier thickness of 12 nm or more, were shown to be anartifact due to incomplete milling of one of the superconducting electrodes.