  Because of its stability, the polarity of a magnetic vortex core (VC) is a
candidate for binary data storage. Switching can be accomplished, e.g, by
driving the VC above a critical velocity $v_c$. Here, we report on controlled
and repeated switching of VC polarity by significantly reducing $v_c$ locally.
We excite vortex dynamics in thin Permalloy disks with a magnetic field pulse,
and map the two-dimensional VC trajectory using time-resolved Kerr microscopy.
In pristine samples, we observe normal gyrotropic motion of the VC. After
laser-induced generation of defects, however, we observe repeated VC reversal
at much-reduced critical velocities as low as 20 m/s. Micromagnetic simulations
reveal how local reduction of exchange coupling can create VC reversal sites
for deterministic VC switching.
