MAGNETIC-RELAXATION OF BIPBSRCACUO HIGH-T-C SUPERCONDUCTORS - ACTIVATION-ENERGIES AND ISOCHRONAL SPECTRUM

The time evolution of the field-cooled magnetic susceptibility (field cooling and then removing the field) has been studied in polycrystalli ne samples of Bi0.7Pb0.3SrCaCu1.8Ox in the temperature range 77 to 110 K. The isothermal curves chi(t, T) have been analyzed to extract the information contained about the nature of the sample relaxation. The t ime evolution of the susceptibility can be explained in terms of therm ally activated processes whose parameters are obtained by means of dif ferent approximations (one and two Debye processes and box distributio n). We present also the isochronal relaxation curves which are achieve d by means of linear filtering operation acting on the isothermal curv es.