Crossover between short and long range proximity effects in SFS junctions with Ni-based ferromagnets

TL;DR

This study investigates how the structural properties of Ni-based ferromagnets influence proximity effects in superconductor/ferromagnet/superconductor junctions, revealing a crossover from short to long-range effects depending on alloy purity.

Contribution

It demonstrates that the purity and structural properties of Ni-based ferromagnets significantly affect proximity effects, highlighting the potential for using clean ferromagnets in superconducting spintronics.

Findings

Supercurrents are larger in pure Ni than in disordered alloys.

A crossover from short to long-range proximity effects occurs with increasing Ni concentration.

Structural properties of ferromagnets are crucial for proximity effects in SFS junctions.

Abstract

We study Superconductor/Ferromagnet/Superconductor junctions with CuNi, PtNi, or Ni interlayers. Remarkably, we observe that supercurrents through Ni can be significantly larger than through diluted alloys. The phenomenon is attributed to the dirtiness of disordered alloys leading to a short coherence length despite a small exchange energy. To the contrary, pure Ni is clean resulting in a coherence length as long as in a normal metal. Analysis of temperature dependencies of critical currents reveals a crossover from short (dirty) to long (clean) range proximity effects in Pt1-xNix with increasing Ni concentration. Our results point out that structural properties of a ferromagnet play a crucial role for the proximity effect and indicate that conventional strong-but-clean ferromagnets can be advantageously used in superconducting spintronic devices.