LOW-FREQUENCY AND LOW MAGNETIC-FIELD EFFECTS ON THE ALTERNATING-CURRENT VOLUME SUSCEPTIBILITY OF CUPRATE SUPERCONDUCTORS

The real and imaginary parts of the alternating current volume suscept ibility are simultaneously measured on a cylindrical sample of ceramic superconducting YBa2Cu3O7-delta in the frequency range from 0.5 to 1 X 10(3) Hz. A relatively small frequency dependence of the shielding d iamagnetism is observed below 2 Hz and above 250 Hz. A logarithmic dep endence of the peak loss temperature is observed which is characterist ic of an activated process with an activation energy of 2.5 eV. A weak decrease of the shielding signal takes place when the amplitude of th e alternating current magnetic field is increased from 0.002 to 0.02 G . Above 0.02 G this shielding signal is field independent. The data ar e interpreted in terms of flux creep and viscous drag effects.