Andreev reflection and spin polarization measurement of Co/YBCO junction

TL;DR

This study measures spin polarization in Co/YBCO heterostructures using temperature-dependent Andreev reflection, finding a consistent 34% polarization up to 70 K, with implications for spintronic applications.

Contribution

It provides the first detailed temperature-dependent spin polarization measurement of Co/YBCO junctions using modified BTK theory.

Findings

Spin polarization in Co is approximately 34% up to 70 K.

YBCO films are grown in (001) orientation with stable critical current density.

The Co films do not significantly alter YBCO's superconducting properties.

Abstract

We report temperature dependent Andreev reflection measurements of Co/ Y$_{1}$Ba$_{2}$Cu$_{3}$O$_{7-\delta}$ (YBCO) heterostructure samples with junction areas of 1 $\mu$m diameter. Modelling of the 5-70 K conductivity data according to a modified Blonder-Tinkham-Klapwijk theory yields a spin polarization in Co film amounting to 34% which is almost constant up to 70 K. The YBCO films have been grown by pulsed laser deposition on sapphire substrates. The Co films are deposited by thermal evaporation on YBCO. The film is characterized by powder X-ray diffraction measurements which shows YBCO is grown in (001) direction.The critical current density, 5 x 10$^{6}$ A/cm$^{2}$, in YBCO remains nearly constant after deposition of Co at zero field and 77 K.