Comparative analysis of the determination of J(c) of YBCO films at different temperatures and magnetic fields by means of the shielding technique

Imaginary susceptibility of YBCO films was studied between 32 and 83 K as a function of magnetic field (0 to 350 Oe). No maximum in the curve of susce ptibility was observed at low temperatures ((i)50 K), this made that this c riterion for the determination of the critical current density could not be applied. The same fact ocurred in the curves of the third harmonic against magnetic field. Therefore, to determine J(c) we proposed the criterion of taking the maximum of the third/first harmonic ratio. It was observed that the J(c) values determined with the three criteria tend to coincide as they approach to the critical temperature.