Proximity Effect in Superconducting-Ferromagnetic Granular Structures

TL;DR

This study investigates how the proximity effect influences superconducting-ferromagnetic granular films, revealing a slow decay and saturation of critical temperature, and suggests non-collinear magnetization induces triplet pairing.

Contribution

It introduces a multilayer model to fit experimental data, highlighting the role of non-collinear magnetization in triplet Cooper pairing in granular structures.

Findings

Critical temperature decays slowly with Ni concentration

Data fits better with a multilayer model

Non-collinear magnetization may induce triplet pairing

Abstract

We examined the proximity effect in granular films made of Pb, a superconductor, and Ni, a ferromagnet, with various compositions. Slow decay of the critical temperature as a function of the relative volume concentration of Ni per sample was demonstrated by our measurements, followed by a saturation of T$_c$. Using an approximate theoretical description of our granular system in terms of a layered one, we show that our data can only be reasonably fitted by a multilayer model. This indicates the importance of the interplay between different ferromagnetic grains; when non-collinearly magnetized they should lead to triplet Cooper pairing.