date:Katholieke Univ Leuven, INPAC Inst Nanoscale Phys & Chem, Nanoscale Supercond & Magnetism & Pulsed Fields G, B-3001 Louvain, Belgium; Univ Santiago de Compostela, LBTS, Dept Fis Mat Condensada, E-15782 Santiago De Compostela, Spain
By using the nonlinear Ginzburg-Landau equations, we investigate symmetry-breaking effects at temperatures well below the normal-superconducting phase boundary, T-c(H), in a superconducting microsquare with a magnetic dot on top under a perpendicular magnetic field. Vorticity values forbidden by the inhomogeneous field of the dot at T-c(H) are progressively recovered deep inside the superconducting state. This restoration of the increase of the fluxoid quantum number by 1 with decreasing temperature is achieved both by the conventional flux expulsion and by the spontaneous generation of additional vortices. The associated transitions between vortex states can be detected experimentally by measuring the temperature dependence of the magnetization.