The properties of co-sputtered YBa2Cu3O7 and CeO2 thin films

Abstract

We have investigated the morphology and superconducting properties of off-axis co-sputtered thin films of YBa2Cu3O7 and CeO2. The composite films were made with CeO2 concentrations up to approximately 43%. Morphology investigations using x-ray diffraction and scanning electron microscopy suggest that films with less than 29% CeO2 may consist of a distorted YBCO crystal structure with Ce being incorporated into the lattice. Films with more than 29% consist of a new material phase. Tc and resistance ratio decreased with increasing CeO2 concentration. Degradation of Tc after photoresist processing was observed for films with higher amounts of CeO2. However, this degradation was reversed and Tc improved beyond that of the as-deposited film by processing the films with an oxygen plasma etch. The temperature dependence of the critical current near Tc showed two power law dependence regions with a crossover near 0.99 Tc for films having low concentrations of CeO2. This crossover shifted to lower temperatures for films with higher amounts of CeO2. Ic’s were decreased by small applied magnetic fields, and for some samples response was observed which was greater than 0.5 mA/G and increased with decreasing temperature. For a sample having 26% CeO2, a 40% reduction in critical current for a 2 G applied field was observed. These magnetic field responses indicate that this material may be a promising candidate for the development of Josephson vortex flow devices.