MAGNETIC-FLUX PENETRATION PROCESS IN 2-DIMENSIONAL SUPERCONDUCTOR COVERED WITH FERROMAGNETIC PARTICLE ARRAY

The magnetostatic effect of a ferromagnetic particle array on an under lying two-dimensional superconducting Nb thin film was investigated in terms of flux penetration processes by means of high sensitive magnet ometry. For bare Nb film, a large drop in magnetization due to a flux rearrangement appeared in the low field region below 2.5 mT. However, once magnetic particles were fabricated on the surface of the Nb film, the drop was not observed. In this configuration, the ferromagnetic p articles seem to behave as flux guides for the external magnetic field , whereby the flux distribution inside the superconductor is well regu lated. Furthermore, a periodical oscillation was observed in the hyste resis loops. This behavior is associated with a flux quantization in t he regions where the superconductivity is suppressed by the stray fiel d of the ferromagnetic particles. The local flux density distribution around the ferromagnetic particles was evaluated by using the London e quation, and the magnetization curve of the Nb film with periodically modulated superconducting order parameter was calculated. (C) 1996 Ame rican Institute of Physics.