Scanning Hall probe microscopy observation of flux pinning in a Pb film covering an array of Co dots

High-resolution scanning Hall probe microscopy (SHPM) has been used to inve stigate the superconducting properties of a thin ph film covering a square array of rectangular submicron Co dots, After magnetization, all the dots a re shown to be in a single-domain magnetic state with dipole stray field di stributions. As the sample is cooled through the critical temperature of th e Pb film at B = 0 we observe strong screening of the dipole fields that we attribute to fluxoid quantization in the superconducting state, Upon cooli ng in applied perpendicular fields we show that the first flux line is sele ctively pinned at the pole of the magnet with the opposite sign of stray fi eld. Ordered vortex structures, which are commensurate with the underlying pinning array, are observed at fields up to twice the matching field. At fi elds in excess of the first matching held, each pinning site appears to be capable of trapping at least two flux lines and no evidence is seen for int erstitial vortices up to twice the matching field at temperatures well belo w the critical temperature of the covering Ph film. Copyright (C) 2000 John Wiley & Sons, Ltd.