Vortex-matter manipulation in nanometer-thin type-II superconducting layers plays a substantial role in the performance of related superconducting devices. A traditional way to avoid deterioration of their transport characteristics is to immobilize the magnetic flux lines by natural or artificially introduced pinning sites inside the nanolayer. An alternative approach can be realized in a planar superconductor-based bilayer with a nanometer-thin ferromagnetic film in close proximity. The interaction between Abrikosov vortices and the magnetization texture in a ferromagnetic layer can provide a pinning potential for them. The effect, called magnetic pinning, is the focus of our research aimed to study coupled metallic multilayers based on different combinations of a weak diluted ferromagnetic (NiCu) and superconducting (NbN) films. The latter include those with an ultra-thin insulating interlayer between the two strips, thus cutting off short-range proximity effect. Measurements of the temperature effect on current–voltage curves for samples with different stacking order of the contacting films have been performed. In some configurations, we found a strong growth of the critical current followed by moderate changes in the critical temperature or their complete absence. Related analysis shows that the underlying mechanism is indeed magnetic vortex pinning that can be enhanced further through magnetization engineering enabling optimization of the pinning strength in desired field ranges.
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This work was partly supported by the joint Ukrainian-Slovak project “Hybrid superconductor devices for neuromorphic applications” funded by the Ministry of Education and Science of Ukraine, the German-Ukrainian collaborative project “Controllable quantum-information transfer in superconducting networks” (DFG project SE 664/21–1, No. 405579680), and the Slovak Research and Development Agency under contracts no. APVV-19–303 and APVV-19–365. E.Zh. acknowledges financial support from Deutscher Akademischer Austauschdienst (DAAD) under the grant “Non-unitary quantum devices as p-bites for stochastic computing”, the funding program 57552335. M.B. is grateful for the financial support from Volkswagen Stiftung under the grant 9B884 “Novel quantum platforms for cryogenic sensing and stochastic computing”.
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Zhitlukhina, E., Poláčková, M., Volkov, S. et al. Critical current enhancement in a superconducting nanolayer proximitized to a weak-ferromagnetic film. Appl Nanosci 13, 4771–4777 (2023). https://doi.org/10.1007/s13204-022-02614-3