Electrical and magnetic properties of twin-free single-crystal praseodymium-doped YBa2Cu3O7-d

We have grown high quality single crystals of Y1-xPrxBaiCu30 7_8 (Pr-doped YBCO), and have succeeded in detwinning them by applying uniaxial stress. The quality of these samples was shown by both magnetic and electrical transport measurements. Each of these methods showed that our samples had sharp superconducting transitions. We measured the magnetic relaxation of four detwinned single crystals of Y1-xPrxBa2Cu307.o, with x = 0, 0.1, 0.2, and 0.3, in a magnetic field of0.5T applied parallel to the c-axis of each sample. Using the Anderson-Kim model ofthermally activated flux-creep, we calculated the effective flux pinning energy, U, for each sample. The results show that for Tffc 0.45, U shows a clear maximum at x = 0.2. In addition, we measured magnetic hysteresis loops for each sample at T/Tc = 0.1, 0.5, and 0.8. We found that the samples exhibit a strong "fish-tail" effect, and, of particular interest, that the sample with x = 0.1 shows two peaks in addition to the zero-field peak. Because of the "fish-tail" effect, we have not been able to obtain a clear picture of the temperature and Pr concentration dependences of the critical current density. However, at temperatures near Tc, our results indicate that a higher flux pinning energy correlates with a higher critical current density. We measured the normal and mixed state Hall and longitudinal resistivities of detwinned Y1.xPrxBa2Cu307..g single crystals, with x = 0.05, 0.10, 0.15, and 0.20. Our normal-state measurements show that Pr-doping in YBCO reduces the charge carrier density. Below Tc, the samples with x = 0.05 and 0.10 exhibit a sign reversal of the Hall resistivity as the magnetic field is increased. However, the sign reversal is absent in the samples with x = 0.15 and 0.20. We have calculated the in-plane Hall conductivity, and find that it can be expressed as the sum of two terms, CtiH and C2H. C1 and C2 are independent of field, but depend on temperature and Pr concentration. The temperature dependences ofC1 and C2 weaken with increasing Pr concentration up to the disappearance of the sign reversal, at which point C1 changes sign and begins to depend more strongly on temperature again. We were the first to analyze Hall effect data in this way (i.e., in terms ofC1 and C2) on a superconductor. Since then, this method of analysis has become one of the standards in high-T c Hall effect studies. To date, we are the only group to have published data on twin-free Pr-doped YBCO single crystals. These samples are hard to grow, and detwinning them is a challenging undertaking.U of I OnlyThesi