Critical Currents of Ex-Situ YBa2Cu3O7-δ Thin Films on Rolling Assisted Biaxially Textured Substrates: Thickness, Field, and Temperature Dependencies
- ORNL
- University of Wisconsin, Madison
The critical current density J{sub c} flowing in thin YBa{sub 2}Cu{sub 3}O{sub 7-{delta}} (YBCO) films of various thicknesses d has been studied magnetometrically, both as a function of applied field H and temperature T, with a central objective to determine the dominant source of vortex pinning in these materials. The films, grown by a BaF{sub 2} ex situ process and deposited on buffered rolling assisted biaxially textured substrates ('RABiTS') substrates of Ni-5% W, have thicknesses d ranging from 28 nm to 1.5 {micro}m. Isothermal magnetization loops M(H;T) and remanent magnetization M{sub rem}(T) in H=0 were measured with H{parallel}c-axis (i.e., normal to film plane). The resulting J{sub c}(d) values (obtained from a modified critical state model) increase with thickness d, peak near d-120 nm, and thereafter decrease as the films get thicker. For a wide range of temperatures and intermediate fields, we find J{sub c} {infinity} H{sup -{alpha}} with {alpha}-(0.56-0.69) for all materials. This feature can be attributed to pinning by large random defects, which theoretically has power-law exponent {alpha} = 5/8. Calculated values for the size and density of defects are comparable with those observed by TEM in the films. As a function of temperature, we find J{sub c}(T,sf)-[1-(T/T{sub c}){sup 2}]{sup n} with n-1.2-1.4. This points to '{delta}T{sub c} pinning' (pinning that suppresses T{sub c} locally) in these YBCO materials.
- Research Organization:
- Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
- Sponsoring Organization:
- USDOE Office of Science (SC)
- DOE Contract Number:
- DE-AC05-00OR22725
- OSTI ID:
- 1003299
- Journal Information:
- Physical Review B, Vol. 73, Issue 13; ISSN 1098--0121
- Country of Publication:
- United States
- Language:
- English
Similar Records
The Incorporation of Nanoscale Columnar Defects Comprised of Self-Assembled BaZrO3 Nanodots to Improve Flux-Pinning and Critical Current Density of NdBa2Cu3O7-δ Films Grown on RABiTS
Correlation Between Grain and Grain-Boundary Critical Current Densities in ex situ Coated Conductors with Variable YBa2Cu3O7- δ Layer Thickness