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 theoreticalT_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 theT_c(H) boundary have been found, including strong asymmetry with respect to the field polarity. [ABSTRACT FROM AUTHOR]