Long range spin supercurrents in ferromagnetic CrO$_2$ using a multilayer contact structure

TL;DR

This study demonstrates long-range supercurrents in fully spin-polarized CrO$_2$ films using a multilayer contact structure, revealing enhanced critical currents likely due to spin mixing facilitating triplet correlations.

Contribution

It introduces a novel multilayer contact arrangement that enables long-range supercurrents in CrO$_2$, advancing understanding of spin triplet supercurrents in ferromagnetic materials.

Findings

Supercurrents observed over nearly a micrometer distance.

Critical current density significantly higher with multilayer contacts.

Spin mixing in the contact structure aids in triplet supercurrent generation.

Abstract

e report measurements of long ranged supercurrents through ferromagnetic and fully spin-polarized CrO$_2$ deposited on TiO$_2$ substrates. In earlier work, we found supercurrents in films grown on sapphire but not on TiO$_2$. Here we employed a special contact arrangement, consisting of a Ni/Cu sandwich between the film and the superconducting amorphous Mo$_{70}$Ge$_{30}$ electrodes. The distance between the contacts was almost a micrometer, and we find the critical current density to be significantly higher than found in the films deposited on sapphire. We argue this is due to spin mixing in the Ni/Cu/CrO$_2$ layer structure, which is helpful in the generation of the odd-frequency spin triplet correlations needed to carry the supercurrent.