The Hall sensor array is a useful tool for measuring local magnetic fields. An array of miniature Hall sensors has been used to study the flux penetration in a ferromagnetic/superconducting (F/S) bilayer consisting of Nb or YBaCuO as the S layer and the Co/Pt multilayer with perpendicular magnetic anisotropy as the F layer, separated by an amorphous Si layer to avoid proximity effect. The F layer is first premagnetized to different magnetization reversal stages to obtain various magnetic domain patterns. The effect of these domain patterns on the flux behavior in the S layer is then studied at various temperatures in the superconducting state. We have observed in the F/S bilayer with Nb that some domain patterns strongly increase the first penetration field indicating the formation of barrier at the sample edge. Further flux penetration shows a complicated pattern, including the regions of flux jumps separated by flat terraces. These effects are not detectable by the global SQUID magnetometry and persist to high temperatures, close to the superconducting transition temperature. Effects observed in the bilayer with YBaCuO are quite different. We discuss the origins of the observed flux penetration pattern.

Supported by the French-Polish Bilateral program "Polonium".

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