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,Tc(H), has been analyzed in the framework of the linearized Ginzburg-Landau theory. A very good agreement has been found between the theoreticalTc(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 theTc(H) boundary have been found, including strong asymmetry with respect to the field polarity. [ABSTRACT FROM AUTHOR]