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Permanent link (DOI): https://doi.org/10.7939/R3280570F

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Vortex dynamics and supercurrents in Bi-2212 superconducting single crystals and films Open Access

Descriptions

Other title
Subject/Keyword
Thin films
Crystallography
Superconductors
Vortex-motion
Type of item
Thesis
Degree grantor
University of Alberta
Author or creator
Ma, Rongchao
Supervisor and department
Jung, Jan A. (Physics)
Examining committee member and department
Kravchinsky, Vadim A. (Physics)
Pavuna, Davor (Physics, Ecole Polytechnique Federale de Lausanne)
Chow, K. H. ( Physics)
Gu, Yu Jeffrey (Physics)
Etsell, Thomas H. (Chemical and Materials Engineering)
Department
Department of Physics
Specialization

Date accepted
2009-10-09T18:05:31Z
Graduation date
2009-11
Degree
Doctor of Philosophy
Degree level
Doctoral
Abstract
The magnetic properties of $Bi_2Sr_2CaCu_2O_{8+x}$ (BSCCO) single crystals and thin films have been studied systematically with a contactless Hall probe system. The BSCCO single crystals of $T_{c} \simeq$ 92 K were grown using a crucible-free optical floating-zone technique. The thin film disks of $T_{c} \simeq$ 82 K were grown using magnetron sputtering technique. Our findings are as follows:\\ \\ 1. The vortex penetration process is strongly time dependent. The penetration time scale varies and depends on the temperature, the applied field and the geometry of the sample.\\ \\ 2. The persistent current relaxations and the effective energy barrier against vortex motion is investigated in a ring-shaped Bi$_2$Sr$_2$CaCu$_2$O$_x$ single crystal. The results show a transition from a strongly non-logarithmic regime to a logarithmic one with increasing temperature. The vortex dynamics in the non-logarithmic regime are insensitive to changes in the microstructure (decreasing oxygen content), but the relaxations in the logarithmic regime are strongly affected by the microstructure.\\ \\ 3. A peak in the temperature dependence of the trapped vortex field is observed at a temperature below the vortex melting line. Logarithmic and non-logarithmic dependence on time were observed in the magnetic relaxations at temperatures below and above the peak, respectively. The results suggest the presence of the vortex-depinning transition at temperatures below the melting line of BSCCO.\\ \\ 4. Vortex penetration, vortex relaxation and vortex-depinning transition in YBCO single crystal are found qualitively similar to that of BSCCO superconductor, but quantitively different. These difference are supposed to be caused by the strong anisotropy in BSCCO superconductor.
Language
English
DOI
doi:10.7939/R3280570F
Rights
This thesis is made available by the University of Alberta Libraries with permission of the copyright owner solely for the purpose of private, scholarly or scientific research. This thesis, or any portion thereof, may not otherwise be copied or reproduced without the written consent of the copyright owner, except to the extent permitted by Canadian copyright law.
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