Electroplated high-aspect-ratio ferromagnetic nanopillars and their application to Ferromagnet-Superconductor Hybrids

We have fabricated highly ordered arrays of high-aspect-ratio ferromagnetic nanostructures, with the long dimension oriented perpendicular to the sample plane. These high-aspect-ratio nanopillars can create highly local magnetic fields. Two earlier problems during the fabrication of these structures by thermal evaporation were (1) a poor lift-off process due to deposition on the sidewalls of the patterned resist, and (2) non-conformal step-coverage. In order to remove these problems, we employed a combination of two techniques: Electron Beam Lithography and electroplating with a conventional three-electrode cell. This significantly improved the quality, compared to thermally evaporated nanopillars, such that scanning electron micrographs demonstrate high order and fidelity. This better quality and yield of the ferromagnetic nanopillars were directly applied to Ferromagnet-Superconductor Hybrids, by growing arrays of ferromagnetic nanopillars on superconducting thin films, while maintaining electrical isolation to prevent a proximity effect. Unlike the control sample, the magnetized Ferromagnet-Superconductor Hybrid showed hysteric behavior and a matching field effect.