Goran Tripun Karapetrov

This article examines the occurrence of mesoscopic effects in superconductor-ferromagnet hybrids. It begins with an overview of theories underpinning superconducting/ferromagnetic (S/F) hybrid structures, focusing on their vortex nucleation conditions and vortex behavior as well as the localized nucleation of superconductivity in an ideal S/F system. It then presents experimental measurements of the localized superconducting state in the cases of domain wall and reverse domain superconductivity, along with the vortex state in planar S/F hybrids. In particular, it considers nucleation thresholds for superconducting vortices and equilibrium vortex configurations. Finally, it discusses the results of local scanning probe measurements of the novel mesoscopic effects that emerge in magnetically coupled S/F hybrid structures in the absence of proximity effects.

Superconducting vortices are a well known class of vortices, each of them carrying a single magnetic flux quantum. In this chapter the authors present the results of low temperature Magnetic Force Microscopy experiments to investigate the nucleation and dynamics of superconducting vortices in magnetically coupled Superconductor/Ferromagnet (S/F) heterostructures made by Nb/Py. It is here shown that by controlling the thicknesses of both S and F layer, the formation of spontaneous vortex-antivortex pairs (V-AV) can be favored and their confinement and mobility can be tuned. The experimental results are compared with two theoretical models dealing with the spontaneous nucleation of V/AV pairs in the limits of S thickness respectively greater and smaller than the London penetration depth. It is shown that vortex nucleation and confinement is regulated by the intensity of the out-of-plane component of the magnetization with respect to a critical magnetization set by the thickness of both S and F layers. Additionally, external field cooling processes were used to probe in-field vortex nucleation and V-AV unbalancing, whereas the sweeping of an external magnetic field when below the superconducting critical temperature was used to force the vortex into motion, probing the vortex mobility/rigidity and the vortex avalanche events.