Title: Geometrical dependence of domain wall propagation and nucleation fields in magnetic domain wall sensor devices,
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.