Publication Date


Document Type


First Advisor

Crabtree, George (Physicist)

Degree Name

M.S. (Master of Science)

Legacy Department

Department of Physics


Vortex-motion; Imaging systems; High temperature superconductors; Magnetic flux; Magnetooptical devices


The production of useful devices from high temperature superconductors relies on the creation of microstructural defects which pin vortices, thereby preserving the ability of a type II superconductor to carry a lossless current. Until recently, the effect of different types of defects on pinning vortices has been mainly studied by methods which determine the average response of a sample. These techniques are by definition insensitive to the local pinning and de-pinning events which are of interest. This thesis addresses the subject of determining the local pinning properties of a defect. A magnetooptical technique will be utilized for observing the motion of magnetic flux lines in a superconductor, thus allowing a characterization of the local pinning properties of different defects. In particular, the design and construction of a miniature gas-flow cryostat will be described. Next, this cryostat is utilized in conjunction with a polarized light microscope for characterizing the pinning properties of twin boundaries in the Y 1B2C3O7.5 superconductor. Twin boundaries are found to exhibit anisotropic critical currents which are both temperature and field dependent.


Includes bibliographical references (pages [77]-80)


vii, 80 pages




Northern Illinois University

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