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Flux Pinning Energy in Nd1-x Smx Ba2Cu3 O7-δ

Mokhtari, Parisa | 2018

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 50470 (04)
  4. University: Sharif University of Technology
  5. Department: Physics
  6. Advisor(s): Akhavan Farshchi, Mohammad
  7. Abstract:
  8. Physical properties of $Re_1 Ba_2 Cu_3 O_{7-\delta} (Re123)$ high-temperature cuprate superconductors attract many of physicists due to their high transition temperature (above Nitrogen boiling point), relatively simple synthesizing and high critical current density. Among this family, Nd123 and Sm123 single-crystal compounds have the highest transition temperature and critical current density in the magnetic fields less than 2 Tesla. In addition, due to the near ionic radius of Nd and Sm elements, it is possible to synthesize $Nd_{1-x} Sm_x Ba_2 Cu_3 O_{7-\delta} (0 \leq x \leq 1)$ compounds with no significant dislocation. In order to investigate the effects of such doping on electrical and flux pinning properties, in this thesis, single-phase polycrystalline $Nd_{1-x} Sm_x Ba_2 Cu_3 O_{7-\delta}$ compounds were prepared using standard solid-state reaction method. Suitable calcination and sintering temperature ranges were determined utilizing the TGA and DTA analysis for $x = 0$ and $1$. Transition temperatures were optimized to about 96 Kelvin by adjusting the sintering temperature to the efficient one. X Ray Diffraction analysis and Rietveld refinements confirm the dominant 123 phase formation. Also the lattice parameters of these samples were in agreement with the reports for the single crystals. Afterward, compounds for $x = 0.25, 0.3, 0.4, 0.5,$ $ 0.6, 0.7, 0.75$ were prepared, and they exhibit all lower onset transition temperatures and wider transition than the Nd123 and Sm123 superconductors. Flux dynamics and doping effects on pinning energy were studied using magnetoresistance measurements, and applying thermally activated flux creep (TAFC) model. Like the other cuprates, temperature dependence of the pinning energy in Arrhenius plots indicates 2D behaviour. Flux pinning energy in the doped compounds improved for $x > 0.5$, and the maximum pinning energy was for Sm123 in all the magnetic fields. The observed magnetic flux pinning trend suggests no modification in the pinning energy and critical current density in the substances included Nd and Sm coexistently rather than Sm123, due to the weak intra-grain Josephson links
  9. Keywords:
  10. Cuprate Superconductors ; High Temperature Superconductor ; Magnetic Resistance ; Thermally Activated Flux Creep (TAFC)Model ; Flux Pinning Energy

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