Magnetic studies of current conduction and flux pinning in high-Tc cuprates: Virgin, irradiated, and oxygen deficient materials

To increase the current density and pinning of magnetic flux in high temperature superconductors, defects with point‐like and line‐like geometries were created in controlled numbers using ion irradiation methods. Single crystals of Y1Ba2Cu3O7 and Bi2Sr2Ca1Cu2O8 superconductors were studied using dc magnetic methods. These studies showed greatly increased irreversibility in the vortex state magnetization and enhanced intergrain current density Jc following irradiation. Linear defects, created by irradiation with energetic heavy ions, are particularly effective in pinning vortices at higher temperatures and magnetic fields. Further investigations of ‘‘flux creep’’ (the time dependence of magnetization) are well described by recent vortex glass and collective pinning theories. Complementary investigations have delineated the role of oxygen deficiency δ on pinning in aligned Y1Ba2Cu3O7−δ materials.