Nanosized Pinning Sites in HTSC Compounds

Abstract

Due to the small coherence lengths of the high-Tc compounds, effective pinning sites are defects or particles of nanometer size according to ξ3. Integral magnetic measurements of the magnetization as a function of temperature in large applied magnetic fields (up to 7 T) have revealed that practically all high-Tc compounds are spatially inhomogeneous, which can be caused by oxygen deficiency (YBCO), solid solutions of Nd/Ba (NdBCO and light rare earth 123-type compounds), intergrowths (Bi-based superconductors), and doping by pair-breaking dopants like Zn, Pr, etc. Various irradiation experiments by neutrons, protons, and heavy-ions have enabled the artificial introduction of effective pinning sites into the high-Tc samples, thus creating many different observations in the magnetic data. From all these observations, we construct a pinning diagram explaining many features observed in high-Tc samples.