Fabrication and Characterization of Nano-Sized Magnetic Structures and Their Flux-Pinning Effects on Superconducting Thin Films

Abstract

This dissertation describes experimental studies of how a spatially alternating magnetic field can effectively pin the magnetic flux in a superconducting thin film (Pb 82 Bi18), thereby enhancing the superconductivity. The spatially alternating magnetic field was provided by a periodic array of nano-sized magnetic structures: 300 nm spacing triangular array of cobalt rods with 100 nm diameter and 300 nm height. The superconducting film deposited on top of the magnetic structures, or an embedded Ferromagnet- Superconductor Hybrids (FSH), showed enhanced critical current and critical magnetic field. The embedded FSH also showed the field matching effect, the field compensation effect, and hysteresis. This dissertation also explains how to fabricate and characterize magnetic nano- structures. Electron beam lithography and electroplating method were used to fabricate the magnetic nanostructures. Scanning electron microscopy (SEM) and atomic force microscopy (AFM) were used to characterize the structures of the magnetic rods. Magnetic force microscopy (MFM) was used to study their magnetic properties.