Mutual inductance critical current measurements in oxygen-deficient YBa2Cu3O7-delta thin films

Comparative studies of a standard four-contact DC method and a contactless mutual inductance setup have been carried out on the temperature dependence of the critical current of YBa2Cu3O(7-delta (YBCO) thin films. The DC measurements are restricted to low currents due to contact heating, whereas the mutual inductance method works well at higher currents. The temperature dependence of the values obtained by the two methods agrees fairly well in the temperature window accessible by both of them. Hence the DC values can be used to calibrate the mutual inductance ones. Thus, the critical current can be determined in a larger temperature range as compared to simple DC measurements. We have applied both techniques to two films with oxygen deficiencies delta of 0.08 and 0.31. The obtained calibration factor allowed us to determine the critical current density of a third sample with delta = 0.24 inductively. The critical current density drops dramatically with the oxygen content. At T/T-c = 0.80, the critical current of the film with delta = 0.08 is more than 40 times larger than that of the film with delta = 0.31.