Superconductor-ferromagnet nanocomposites created by co-deposition of niobium and dysprosium

TL;DR

This study demonstrates the creation of superconductor-ferromagnet nanocomposites via co-deposition of niobium and dysprosium, showing enhanced in-field critical current density due to magnetic pinning effects.

Contribution

It introduces a method to produce phase-separated superconductor-ferromagnet composites with tunable magnetic and superconducting properties.

Findings

In-field Jc is greatly enhanced up to 3 T saturation field of Dy.

Phase separation occurs on scales from 5 nm to 1 micron.

Stripe ordering leads to in-plane anisotropy in Jc.

Abstract

We have created superconductor-ferromagnet composite films in order to test the enhancement of critical current density, Jc, due to magnetic pinning. We co-sputter the type-II superconductor niobium (Nb) and the low-temperature ferromagnet dysprosium (Dy) onto a heated substrate; the immiscibility of the two materials leads to a phase-separated composite of magnetic regions within a superconducting matrix. Over a range of compositions and substrate temperatures, we achieve phase separation on scales from 5 nm to 1 micron. The composite films exhibit simultaneous superconductivity and ferromagnetism. Transport measurements show that while the self-field Jc is reduced in the composites, the in-field Jc is greatly enhanced up to the 3 T saturation field of Dy. In one instance, the phase separation orders into stripes, leading to in-plane anisotropy in Jc.