  The pinning of flux lines by two different types of regular arrays of
submicron magnetic dots is studied in superconducting Pb films; rectangular Co
dots with in-plane magnetization are used as pinning centers to investigate the
influence of the magnetic stray field of the dots on the pinning phenomena,
whereas multilayered Co/Pt dots with out-of-plane magnetization are used to
study the magnetic interaction between the flux lines and the magnetic moment
of the dots. For both types of pinning arrays, matching anomalies are observed
in the magnetization curves versus perpendicular applied field at integer and
rational multiples of the first matching field, which correspond to stable flux
configurations in the artificially created pinning potential. By varying the
magnetic domain structure of the Co dots with in-plane magnetization, a clear
influence of the stray field of the dots on the pinning efficiency is found.
For the Co/Pt dots with out-of-plane magnetization, a pronounced field
asymmetry is observed in the magnetization curves when the dots are magnetized
in a perpendicular field prior to the measurement. This asymmetry can be
attributed to the interaction of the out-of-plane magnetic moment of the Co/Pt
dots with the local field of the flux lines and indicates that flux pinning is
stronger when the magnetic moment of the dot and the field of the flux line
have the same polarity.
