The bottom barrier layer of well‐ordered nanoporous alumina membranes reveals a previously unexploited nanostructured template surface consisting of a triangular lattice of hemispherical nanoscale bumps. Quasi‐hexagonal vortex‐pinning lattice arrays are created in superconducting Nb films deposited onto this template (see image). Matching effects are preserved at higher magnetic fields and lower temperatures when compared to holes on the top face.

Dense arrays of ordered ferromagnetic nanowires have been used to create periodic magnetic pinning centers in thin superconducting NbN films. The nanowires were electrodeposited in a highly ordered porous alumina membrane and the thin NbN film was deposited on top of the perpendicularly oriented magnetic nanowires. Matching effects have been observed up to 2.5 T (11th matching field) and are maintained at low temperature. An appreciable enhancement of the superconducting properties is observed. At low fields, a hysteretic behavior in the magnetoresistance is found, directly related to the magnetization processes of arrays of interacting single domain ferromagnetic nanowires.

A simple procedure is described for creating periodic vortex pinning centers in thin superconducting NbN films. We report on three different strategies which involve the use of highly ordered alumina templates. In this approach, NbN thin films are deposited either on the porous face of the template made of a triangular array of nanoholes or on the triangular array of bumps formed by the barrier layer or even on the top of perpendicularly oriented ferromagnetic nanowire arrays obtained by electrochemical deposition, thus forming superconductor-ferromagnet hybrids. In all cases, the ordered template allows NbN films to form a periodic pinning array during its growth. The interpore (or inter-bump) distance ranged between 50 and 100 nm and adjustable pore (or wire) diameter was varied between 30 and 60 nm. Numerous matching effects have been observed up to 2.5 T and are maintained at low temperature. These fields are considerably higher than those typical for periodic pinning arrays made by lithographic techniques, which reflects the benefits of nanostructuring superconductors by using self-organized growth to enhance vortex pinning in a large field and temperature range.

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.

We used oxygen ion irradiation to transfer the nanoscale pattern of a porous alumina mask into high-T(C) superconducting thin films. This causes a nanoscale spatial modulation of superconductivity and strongly affects the magneto-transport below T(C), which shows a series of periodic oscillations reminiscent of the Little-Parks effect in superconducting wire networks. This irradiation technique could be extended to other oxide materials in order to induce ordered nanoscale phase segregation.