Functional properties of single crystals and laser deposited thin films of cubic BKBO superconductors

Magnetic properties of a BKBO single crystal and highly oriented in-situ Pulsed Laser Deposited, PLD, thin film has been investigated. From the hysteretic loops at 5K along three equivalent crystallographic directions we find, that along the growth direction of the crystal the critical current tends to decrease, which is probably due to the nature of defects introduced during the growth. In the PLD films, we find that the rate of cooling to the oxygenation temperature is the important parameter which can be controlled to eliminate micro-cracks and consequently enhance the critical current. From SQUID-data on the single crystal the temperature dependence of the critical current, is found to be J_c(T) = J_co(1-T/T_c)² with J_co = 2.8 10⁴ A/cm² -a value similar to that obtained for the PLD films as well. The field dependence of the critical current at various temperatures for the single crystal is well described by an exponential behaviour which may be considered to be a consequence of the pair breaking perturbation effect.