Resistivity transitions in applied magnetic fields in epitaxial thin films of Fe- and Zn-doped YBa₂Cu₃O_7-δ

Abstract

Epitaxial c-axis-oriented thin films of Fe- or Zn-doped YBa₂Cu₃O_7-δ have been grown on (001) LaAlO₃ substrates by pulsed excimer laser ablation. Adequate substitutional incorporation of Fe atoms required optimal choice of oxygen pressure during deposition as well as a postsynthesis annealing treatment at 550 °C. Zn incorporation did not require such special processing conditions. The resistivity transitions for such high-quality well-characterized films were studied at different magnetic fields up to 5 T. Analysis of T_c depression and change in dH_c2/dT at T_c has been made in terms of the possible changes in the density of states at the Fermi level, contributions of the exchange field, magnetization field, and nonmagnetic scattering. Estimates of the activation energy [U₀(H)] for vortex motion have also been made.