Electrical and magnetic properties of twin-free single-crystal praseodymium-doped YBa2Cu3O7-d
Manson, Jonathan
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https://hdl.handle.net/2142/18840
Description
Title
Electrical and magnetic properties of twin-free single-crystal praseodymium-doped YBa2Cu3O7-d
Author(s)
Manson, Jonathan
Issue Date
1996-05
Doctoral Committee Chair(s)
Ginsberg, D.M.
Department of Study
Physics
Discipline
Physics
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
electrical properties
magnetic properties
ofY1-xPrxBaiCu30 7_8 (Pr-doped YBCO)
Hall effect
Language
en
Abstract
"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 exhibits a weak dependence on Pr concentration, whereas for T/Tc > 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."
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