Periodic vortex pinning with magnetic and nonmagnetic dots: The influence of size

Periodic pinning arrays can give rise to commensurability effects for the v ortex pinning in superconductors. We studied the influence of size and sepa ration of the individual pinning centers made out of magnetic and nonmagnet ic dots. While there is some dependence on the dot size, the periodic pinni ng changes its character drastically, as soon as the separation between dot s becomes comparable to the coherence length of the superconductor. This ca n be understood by a crossover from a weak pinning regime to a superconduct ing wire network regime with decreasing dot separation. In addition, the co mparison between the periodic pinning of magnetic dot arrays and nonmagneti c dot arrays shows that the former generally show more pronounced periodic pinning. This indicates conclusively a magnetic contribution to the pinning mechanism.