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

TL;DR

This study investigates the transport and spectroscopic properties of superconductor-ferromagnet-superconductor junctions using cuprate superconductors and manganite ferromagnetic barriers, revealing conductance features, magnetic field effects, and superparamagnetism signatures.

Contribution

It provides new experimental insights into the conductance spectra and magnetic properties of LSCO-LCMO-LSCO junctions, including the effects of magnetic fields and barrier thickness.

Findings

Conductance spectra show Andreev-like peaks and sub-gap resonances.

Magnetic fields suppress gap features but reveal tunneling background.

Negative magnetoresistance observed after field cycling.

Abstract

Transport and Conductance spectra measurements of ramp-type junctions made of cuprate superconducting $La_{1.9}Sr_{0.1}CuO_4$ electrodes and a manganite ferromagnetic $La_{0.67}Ca_{0.33}MnO_3$ barrier are reported. At low temperatures below $T_c$, the conductance spectra show Andreev-like broad peaks superposed on a tunneling-like background, and sometimes also sub-gap Andreev resonances. The energy gap values $\Delta$ found from fits of the data ranged mostly between 7-10 mV. As usual, the gap features were suppressed under magnetic fields but revealed the tunneling-like conductance background. After field cycling to 5 or 6 T and back to 0 T, the conductance spectra were always higher than under zero field cooling, reflecting the negative magnetoresistance of the manganite barrier. A signature of superparamagnetism was found in the conductance spectra of junctions with a 12 nm thick LCMO barrier. Observed critical currents with barrier thickness of 12 nm or more, were shown to be an artifact due to incomplete milling of one of the superconducting electrodes.