Date of Award
Doctor of Philosophy
Dr. Clement Bums
Dr. Robert Shamu
Dr. Alvin Rosenthal
Dr. Lisa Paulius
This work focuses on the interaction between magnetic vortices in high temperature superconductors and defects introduced by irradiation with protons and heavy ions. The study concentrates on the high temperature superconductor YBa;Cu30 7J5. This material is used to investigate the role of disorder in phase transitions, a topic of great interest in Solid State Physics. In addition, this study analyzes the interaction between vortices and columnar defects in various doses and defect morphologies, including the thermal stability of columnar defects.
We present experimental evidence of the vortex glass phase in proton irradiated Y B a:Cu:!0 -.15. For the first time, evidence for a vortex glass transition is detected in an untwinned single crystal of YBa:Cu:iO-.s with induced point-like disorder. The first order melting transition, present before the irradiation, is suppressed by proton irradiation and a second order vortex glass transition appeared at lower temperatures. Our results suggest that sufficiently high pinning disorder is required in order for the vortex glass phase to be observed.
We then present a study of the effects of heavy ion irradiation on the phase diagram. The effects of the irradiation dose, irradiation ion type, and defect orientation on the pinning are investigated. For irradiation parallel to the c-axis of the crystal, we found that the columnar defects inhibit vortex motion when vortices are parallel to the defects, and they promote vortex motion for vortices perpendicular defects. Also for irradiation in this configuration, we learned that Uranium-induced defects are more efficient pinning sites than Gold-induced defects. For irradiation parallel to the ab-plane, we found that the columnar defects inhibit vortex motion for vortices parallel to the defects.
Finally, the study discusses the thermal stability of columnar defects introduced by irradiation with Gold in YBCO single crystals. The dependence o f the critical current density on the annealing temperatures is correlated with changes in the microstructure of the defects, as seen from transmission electron microscopy measurements. We found an increase in the critical currents at 77K. with annealing, which emphasizes the high suitability of irradiated samples in applications that operate at liquid nitrogen temperatures.
Petrean, Andra, "The Effects of Radiation Damage on the Vortex Dynamics of High Temperature Superconductors" (2000). Dissertations. 1478.