Vortex patterns and nucleation of superconductivity in mesoscopic rectangles and in hybrid superconductor/ferromagnet structures

Nucleation of superconductivity and vortex patterns have been studied in mesoscopic samples providing the crossover between square and rectangular geometries. The measured nucleation line, T _c (H), has been analyzed in the framework of the linearized Ginzburg-Landau theory. A very good agreement has been found between the theoretical T _c (H) boundary and the experimental data for rectangles with different aspect ratios. The superconductor/ferromagnet hybrids, such as magnetic Co/Pd dot in a superconducting loop and the dot on top of a superconducting disk have also been investigated. Pronounced effects of the dot on the T _c (H) boundary have been found, including strong asymmetry with respect to the field polarity.Received: 26 February 2004, Published online: 3 August 2004PACS: 74.25.Dw Superconductivity phase diagrams - 74.78.Na Mesoscopic and nanoscale systems