Abstract
We report measurements of the magnetoresistance of epitaxial thin films with varying oxygen content in magnetic fields H applied parallel (H∥c) and perpendicular (H⊥c) to the tetragonal c axis. We have observed critical scaling of the electrical resistivity that is consistent with a vortex-glass transition for a film with an optimum superconducting transition temperature of ≊22 K and H∥c . The values of the zero-temperature upper critical field (0)=80 kOe and the in-plane zero-temperature coherence length (0)=64 Å were obtained from an analysis of the fluctuation conductivity. For an overoxygenated film with ≊10 K, an anomaly develops with increasing field for H∥c and T≲2 K that is characterized by a minimum in the temperature dependence of the resistivity followed by a second resistive transition at a lower temperature, which is nearly independent of H. This behavior is similar to that previously observed in single crystals and may be associated with the magnetic ordering of the ions. © 1996 The American Physical Society.
- Received 16 April 1996
DOI:https://doi.org/10.1103/PhysRevB.54.3610
©1996 American Physical Society