# Geometrical dependence of domain wall propagation and nucleation fields in magnetic domain wall sensor devices

## TL;DR

This study investigates how geometrical and material factors influence domain wall propagation and nucleation fields in magnetic sensor nanowires, providing statistical insights and modeling to improve device reliability.

## Contribution

It offers a comprehensive statistical analysis of domain wall properties in nanowire sensors, highlighting the influence of material parameters and geometrical factors on device failure modes.

## Key findings

- Propagation field is mainly affected by material parameters.
- Nucleation fields can be modeled with a Stoner-Wohlfarth approach.
- GMR measurements reveal device-to-device variation and upper limits.

## Abstract

We study the key domain wall properties in segmented nanowires loop-based structures used in domain wall based sensors. The two reasons for device failure, namely the distribution of domain wall propagation field (depinning) and the nucleation field are determined with Magneto-Optical Kerr Effect (MOKE) and Giant Magnetoresistance (GMR) measurements for thousands of elements to obtain significant statistics. Single layers of Ni$_{81}$Fe$_{19}$, a complete GMR stack with Co$_{90}$Fe$_{10}$/Ni$_{81}$Fe$_{19}$ as a free layer and a single layer of Co$_{90}$Fe$_{10}$ are deposited and industrially patterned to determine the influence of the shape anisotropy, the magnetocrystalline anisotropy and the fabrication processes. We show that the propagation field is little influenced by the geometry but significantly by material parameters. The domain wall nucleation fields can be described by a typical Stoner-Wohlfarth model related to the measured geometrical parameters of the wires and fitted by considering the process parameters. The GMR effect is subsequently measured in a substantial number of devices (3000), in order to accurately gauge the variation between devices. This reveals a corrected upper limit to the nucleation fields of the sensors that can be exploited for fast characterization of working elements.