Superconducting properties of perforated NbN films using ordered arrays of ferromagnetic nanowires

The superconducting properties of NbN thin films deposited perpendicularly and embedding a 100-nm-spaced triangular array of ferromagnetic nanowires have been studied. Matching effects are found to persist up to 3 T in these superconductor-ferromagnet hybrids. Other interesting matching features have been also observed. The first matching field depends on the magnetic history. It can be shifted practically at will between the theoretical matching field H-1 and a lower field H-1* that depends on the shape of the magnetization hysteretic loop of the nanowires array. Therefore, this shift is strongly influenced by the nanowires packing, in particular by the nanowires diameter in the present system. The reduction of the first matching field is associated with an enhancement of the superconducting state that is the strongest when the first matching field is shifted down to H-1*. Finally, misleading field-induced superconductivity has been observed in fields up to 1.2 T.