Flux pinning by regular arrays of ferromagnetic dots

TL;DR

This study investigates how regular arrays of ferromagnetic dots influence flux pinning in superconducting Pb films, revealing the effects of magnetic stray fields and domain structures on pinning efficiency and flux configurations.

Contribution

It provides new insights into flux pinning mechanisms by ferromagnetic dot arrays, highlighting the role of magnetic stray fields and domain structures in enhancing pinning performance.

Findings

Matching anomalies at rational multiples of the first matching field.

Stray field of in-plane magnetized dots affects pinning efficiency.

Magnetic moment orientation influences flux pinning strength and asymmetry.

Abstract

The pinning of flux lines by two different types of regular arrays of submicron magnetic dots is studied in superconducting Pb films; rectangular Co dots with in-plane magnetization are used as pinning centers to investigate the influence of the magnetic stray field of the dots on the pinning phenomena, whereas multilayered Co/Pt dots with out-of-plane magnetization are used to study the magnetic interaction between the flux lines and the magnetic moment of the dots. For both types of pinning arrays, matching anomalies are observed in the magnetization curves versus perpendicular applied field at integer and rational multiples of the first matching field, which correspond to stable flux configurations in the artificially created pinning potential. By varying the magnetic domain structure of the Co dots with in-plane magnetization, a clear influence of the stray field of the dots on the pinning efficiency is found. For the Co/Pt dots with out-of-plane magnetization, a pronounced field asymmetry is observed in the magnetization curves when the dots are magnetized in a perpendicular field prior to the measurement. This asymmetry can be attributed to the interaction of the out-of-plane magnetic moment of the Co/Pt dots with the local field of the flux lines and indicates that flux pinning is stronger when the magnetic moment of the dot and the field of the flux line have the same polarity.