On the Explanation of the Paramagnetic Meissner Effect in Superconductor/Ferromagnet Heterostructures

TL;DR

This paper investigates the paramagnetic Meissner effect in superconductor/ferromagnet bilayers, proposing a vortex-based model to explain the observed magnetic behavior below the superconducting transition temperature.

Contribution

It introduces a vortex-based model to explain the PME in S/F bilayers, accounting for the magnetic moment's sign, magnitude, and field dependence.

Findings

The model explains the sign and magnitude of the magnetic moment.

The vortex contribution dominates due to the thin S layer.

The model matches experimental field dependence.

Abstract

An increase of the magnetic moment in superconductor/ferromagnet (S/F) bilayers V(40nm)/F [F$=$Fe(1,3nm), Co(3nm), Ni(3nm)] was observed using SQUID magnetometry upon cooling below the superconducting transition temperature Tc in magnetic fields of 10 Oe to 50 Oe applied parallel to the sample surface. A similar increase, often called the paramagnetic Meissner effect (PME), was observed before in various superconductors and superconductor/ferromagnet systems. To explain the PME effect in the presented S/F bilayers a model based on a row of vortices located at the S/F interface is proposed. According to the model the magnetic moment induced below Tc consists of the paramagnetic contribution of the vortex cores and the diamagnetic contribution of the vortex-free region of the S layer. Since the thickness of the S layer is found to be 3-4 times less than the magnetic field penetration depth, this latter diamagnetic contribution is negligible. The model correctly accounts for the sign, the approximate magnitude and the field dependence of the paramagnetic and the Meissner contributions of the induced magnetic moment upon passing the superconducting transition of a ferromagnet/superconductor bilayer.