# Sudden Magnetization Drops in S/F bilayered Structures

## TL;DR

This study investigates abrupt drops in magnetization in Nb/Co bilayers, attributing them to vortex formation caused by stray fields from Bloch Domain Walls, which influence the superconductor's magnetic states.

## Contribution

It provides a direct explanation linking Bloch Domain Wall stray fields to vortex-induced magnetization drops in superconductor/ferromagnet bilayers, expanding understanding of magnetic interactions in such structures.

## Key findings

- Magnetization drops occur near coercive fields due to BDW stray fields.
- Vortices are generated at small fields and removed at high fields close to H_{c2}.
- The mechanism explains previously observed critical current drops.

## Abstract

We report in plane magnetization measurements on Nb/Co bilayers using a thin superconductor Nb$\sim25$ nm and a thick ferromagnet Co$\sim40-55$ nm where Bloch Domain Walls (BDW) are energetically favorable. Here sharp drops in the magnetization are explained as direct consequence of BDW stray fields that induce vortices in the out of plane direction. These are generated at small fields around the coercive field of the ferromagnet and removed at large fields of the order of $H_{c2}$. These two well distinctive magnetic states of the superconductor, with or without out of plane vortices, is the same mechanism used to explain the drops in critical currents reported in [E. J. Pati$\~{n}$o et. al., The European Physical Journal B 68, 73 (2009)]