I= EFFECTS OF FLUX MOTION ON THE ELECTRICAL CONDUCTION IN SOME GRANULAR HIGH Tc SUPERCONDUCTORS-STUDIES IN LOW AND MODERATE MAGNETIC FIELDS
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Title of Thesis
EFFECTS OF FLUX MOTION ON THE ELECTRICAL CONDUCTION IN SOME GRANULAR HIGH Tc SUPERCONDUCTORS-STUDIES IN LOW AND MODERATE MAGNETIC FIELDS

Author(s)
MUHAMMAD MUNEEB ASIM
Institute/University/Department Details
Department of Physics/ Quaid-i-Azam University Islamabad
Session
1996
Subject
Physics
Number of Pages
173
Keywords (Extracted from title, table of contents and abstract of thesis)
flux motion, electrical conduction, granular high tc superconductors, magnetic fields, ybco, bscco, flux flow, flux creep, flux pinning

Abstract
Experimental work has been carried out on YBCO and BSCCO based granular high Te superconductors to explore the mechanism of conduction in applied magnetic field. dc resistivity technique has beep employed to observe the details of dissipation, dependent and independent of the mutual orientation () of J and B. Both ZFC and FC dissipation have been studied. The p(())H.T, p(H,I).To and P(T,I)H,o measurements were taken in the field range 0 < H < 16 KOe and in the temperature range of 77K to 86K. The p( ()) data observed contained both angle independent and angle dependent dissipations. At fields H < H c1, the angle dependent dissipation is comparatively larger than the angle independent part and the case is opposite for fields H >> Hc1 (2 - 16 KOe). The angle dependence has a sin2() variation which is a typical signature of flux flow (Pff). This pff part varies with increasing fields according to a modified flux flow expression, in line with the reported microwave surface resistance data. We study in detail the variation of the modified flux flow (MFF) with temperature, and current. We find that the field dependent exponent in the MFF varies from being close to 1 to 0.4, with increasing degree of vortex disorder due to current or temperature. Similarity between the behavior of YBCO (at higher currents and temperatures) and that reported for BSCCO, is noted and explained. The field, current and temperature variation of angle independent part Pps has also been investigated. At relatively low values of current and at higher temperatures, the data follows an approximated Amegaokar Halperin expression approximated for small value of argument, The field dependence of r has been found to be H-I/3 consistent with some previously reported results obtained by others in the low field region. At low angles the angular part of the dissipation shows deviations from sin20, as well as hysteresis. This low angle anomaly was thoroughly studied at different currents, fields and temperatures and interpreted as an effect of Lorentz force mediated flux redistribution between inter and intragrain regions. A magnetization model was developed to incorporate both the equilibrium and non equilibrium parts of magnetization in the granular samples. The data were fit to M(H) and the values of He2(T) obtained. These values of Mequil were used to fit the pff(H) data.

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S. No. Chapter Title of the Chapters Page Size (KB)
1 0 Contents
93.26 KB
2 1 The Mechanisms Of Dissipation In Superconductors 1
300.96 KB
  1.1 Introduction 1
  1.2 Bardeen -Stephen Model 2
  1.3 Thermally Activated Flux Creep And Flux Flow 4
  1.4 Critical State Model 7
  1.5 Inter And Intra Grain Regions 9
  1.6 Flux Pinning 12
  1.7 Josephson Junction 13
  1.8 Phase Slip Dissipation 15
  1.9 Overview And Motivation Of Thesis 17
3 2 Fabrication And Characterization Of Samples 23
357.75 KB
  2.1 Sample Preparation 23
  2.2 Characterization Of Y Ba 2 cu 3 O y 26
  2.3 Characterization Of [ Bi 1 . 6 ( Pb o,3 so. 1 )]Sr 2 ca 2 cu 3 0 4 37
  2.4 V €“ 1 Characteristics Of Y Ba 2 Cu 3 O 7 €“ Y 39
  2.5 Low Field V (H) Behavior Of Y Ba 2 Cu 3 O 7-Y
4 3 Experimental Set Up 56
50.42 KB
  3.1 Introduction 56
  3.2 Set Up For V( O) Measurement 57
  3.3 Low Field Electromagnet 57
5 4 Magnetization Analysis 61
237.16 KB
  4.1 Introduction 61
  4.2 Analytical Derivation Of Magnetization Equations 63
  4.3 Results 67
  4.4 Conclusion 67
6 5 Flux Flow, Phase Slip And Flux Re-Distribution 86
869.74 KB
  5.1 Introduction 86
  5.2 Motivation And Objectives 91
  5.3 Experimental 93
  5.4 Results 95
  5.5 Low Angle Anomaly 105
  5.6 Low Field Behavior 122
  5.7 High Field Region (500 ‰ H ‰16000 0 e ) 127
  5.8 Angle Independent (Phase Slip) Part Of The Dissipation 149
  5.9 Conclusions 158