Andreev nanoprobe of half-metallic CrO$_{2}$ films using superconducting cuprate tips

TL;DR

This study demonstrates that superconducting cuprate tips can be effectively used as spin-sensitive nanoprobes to analyze the high spin polarization in CrO$_{2}$ thin films through point-contact Andreev reflection spectroscopy.

Contribution

It introduces a novel application of superconducting cuprate tips as nanoprobes for spin-sensitive measurements on ferromagnetic materials.

Findings

Strong suppression of Andreev reflection indicates high spin polarization.

Technique validated against non-magnetic and conventional superconducting tips.

Point contacts are nanoscale and ballistic, suitable for microscopic analysis.

Abstract

Superconducting tips of YBa$_{2} $Cu$_{3}$O$_{7-x}$ were used to perform point-contact Andreev reflection spectroscopy on half-metallic CrO$_{2}$ thin films. At 4.2K, strong suppression of the d-wave Andreev reflection characteristics was observed, consistent with the high spin polarization of CrO$_{2}$. Our technique was validated by comparison with data taken on non-magnetic Au films, and with data taken by superconducting Pb tips. The point contacts were estimated to be $\lesssim$ 10nm in size, attesting to their ballistic and microscopic nature. Our results demonstrate the feasibility of using superconducting cuprate tips as spin-sensitive nanoprobes of ferromagnets.