Macroscopic magnetic properties of single crystalline high-temperature superconductors

Thesis/Dissertation · Thu Dec 31 04:00:00 EST 1992

OSTI ID:115553

Ahang, Lu

Single crystals of Bi{sub 1.7}Pb{sub 0.3}Sr{sub 2}CaCu{sub 2}O{sub 8} were grown by a self flux method. The crystals have dimensions as large as 5 x 10 x 1 mm{sup 3}. The sample quality was examined by scanning electron microscopy. The magnetic measurements indicate superconducting transition temperatures of 96 {+-} 2 K for the best samples of Bi{sub 1.7}Pb{sub 0.3}Sr{sub 2}CaCu{sub 2}O{sub 8}. The hysteresis loops and magnetic relaxations in Bi{sub 1.7}Pb{sub 0.3}Sr{sub 2}CaCu{sub 2}O{sub 8} crystals were measured at various temperatures and fields. The relaxation rate dM/dlnt exhibits strong field dependence in the temperature range 6-20 K. By expanding Bean`s model of the critical current density to include the field dependence of the flux creep effect, we developed expressions for both M and dM/dlnt as a function of field. These expressions were used to fit our experimental data of field dependent magnetization and relaxation rate. Reversible temperature dependent magnetization measurements are conducted on Bi{sub 1.7}Pb{sub 0.3}Sr{sub 2}CaCu{sub 2}O{sub 8} single crystals for fields along the c-axis. A linear temperature dependence of the reversible magnetization has been obtained over a wide temperature range. The value of the magnetization slope dM/dT in the linear region at a fixed field decreases at higher field. Both the large range of rounding of the magnetization near T{sub c} and the field-dependent dM/dT in the Bi{sub 1.7}Pb{sub 0.3}Sr{sub 2}CaCu{sub 2}O{sub 8} system indicate that the traditional extrapolation method based on linear Abrikosov formula near H{sub c2} may not be applied. A new theoretical model is employed to determine the Ginzburg-Landau parameter {kappa} and upper critical field H{sub c2} versus temperature.

• Research Organization: California Univ., Davis, CA (United States)
• OSTI ID: 115553
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
66 PHYSICS
BARIUM COMPOUNDS
BISMUTH COMPOUNDS
CALCIUM COMPOUNDS
COPPER OXIDES
CRYSTAL GROWTH
HIGH-TC SUPERCONDUCTORS
LEAD COMPOUNDS
MAGNETIC PROPERTIES
STRONTIUM COMPOUNDS
TEMPERATURE DEPENDENCE
TRANSITION TEMPERATURE
YTTRIUM COMPOUNDS