Magnetic properties of submicron Co islands and their use as artificial pinning centers

TL;DR

This study investigates elongated submicron Co islands' magnetic properties and their effectiveness as artificial pinning centers in superconducting films, revealing stable domain structures and enhanced flux pinning.

Contribution

It demonstrates the magnetic domain configurations of Co islands and their role as artificial pinning centers in superconductors, with direct visualization and magnetic state dependence.

Findings

Co islands have antiparallel domain structures in as-grown state

Magnetic-force microscopy visualizes a 2x2 checkerboard pattern

Magnetized Co islands serve as effective flux pinning centers

Abstract

We report on the magnetic properties of elongated submicron magnetic islands and their influence on a superconducting film. The magnetic properties were studied by magnetization hysteresis loop measurements and scanning-force microscopy. In the as-grown state, the islands have a magnetic structure consisting of two antiparallel domains. This stable domain configuration has been directly visualized as a 2x2-checkerboard pattern by magnetic-force microscopy. In the remanent state, after magnetic saturation along the easy axis, all islands have a single-domain structure with the magnetic moment oriented along the magnetizing field direction. Periodic lattices of these Co islands act as efficient artificial pinning arrays for the flux lines in a superconducting Pb film deposited on top of the Co islands. The influence of the magnetic state of the dots on their pinning efficiency is investigated in these films, before and after the Co dots are magnetized.