  We theoretically and experimentally analyze the pinning of a magnetic domain
wall (DW) at engineered anisotropy variations in Pt/Co/Pt strips with
perpendicular magnetic anisotropy. An analytical model is derived showing that
a step in the anisotropy acts as an energy barrier for the DW. Quantitative
measurements are performed showing that the anisotropy can be controlled by
focused ion beam irradiation with Ga ions. This tool is used to experimentally
study the field-induced switching of nanostrips which are locally irradiated.
The boundary of the irradiated area indeed acts as a pinning barrier for the
domain wall and the pinning strength increases with the anisotropy difference.
Varying the thickness of the Co layer provides an additional way to tune the
anisotropy, and it is shown that a thinner Co layer gives a higher starting
anisotropy thereby allowing tunable DW pinning in a wider range of fields.
Finally, we demonstrate that not only the anisotropy itself, but also the width
of the anisotropy barrier can be tuned on the length scale of the domain wall.
