Critical current characteristics of composite thin films of Au and YBa2Cu3O7

Thin film composites of YBa2Cu3O7 (YBCO) with gold were deposited by inverted cylindrical magnetron sputtering on SrTiO3 (STO), MgO, and yttrium stabilized zirconium (YSZ) substrates using a bilayer deposition process. The material and electrical properties of crystal structure, surface morphology, resistivity, transition temperature (T-c), resistance ratio, and critical current (I-c) as a function of temperature and small magnetic fields were investigated. Films deposited on STO showed little degradation in superconducting properties up to 500 Angstrom of gold with 1 k Angstrom of YBCO; for YSZ and MgO, the films showed a rapid fall-off in T-c with gold thickness. For YSZ 3-10 Angstrom of gold caused the films to become insulating; however, for gold greater than 25 Angstrom, the films were superconducting but T-c rapidly fell to zero by 500 Angstrom of gold. Composites on MgO showed the most rapid fall-off in T-c going to zero by 200 Angstrom of gold. The temperature dependence of I-c was predominately quadratic. However, some films showed a crossover between quadratic and linear temperature dependence in I-c. The I-c of all the composites showed a response to small magnetic fields with the films on STO being the least sensitive and those on MgO the most. There was a trade-off between T-c and field response with the film having the greatest response having the lowest T-c. These composite films show potential for vortex flow device development. (C) 1999 Published by Elsevier Science B.V. All rights reserved.