Symmetry-breaking effects and spontaneous generation of vortices in hybrid superconductor-ferromagnet nanostructures

Qinghua Chen; Carlos Carballeira; Victor V. Moshchalkov

doi:10.1103/PhysRevB.74.214519

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Symmetry-breaking effects and spontaneous generation of vortices in hybrid superconductor-ferromagnet nanostructures

Qinghua Chen, Carlos Carballeira, Victor V. Moshchalkov

DOI 10.1103/PhysRevB.74.214519 · Physical Review B

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Abstract

By using the nonlinear Ginzburg-Landau equations, we investigate symmetry-breaking effects at temperatures well below the normal-superconducting phase boundary, Tc(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 Tc(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.