On measurement of V-I curves of BSCCO-2223/Ag tapes, a hysteresis was observed during ramping the current up and down over I-c level. The hysteresis was not observed for monofilamentary tapes, but it was frequently present in multifilamentary tapes. Typical electric field in our measurements was from 10(-5) to 10(-1) V/m. The larger the maximum of the voltage, the larger was the hysteresis effect. For a fixed maximum voltage, the larger the ramping rate, the broader was the hysteresis loop. If the change in current was stopped over I-c, the relaxation of the voltage was observed. For ascending curve, the relaxation was negative and voltage decreased with time when current was held constant. For descending curve, it was positive and voltage increased when the current decrease was stopped. The effect was present both for short samples as well as for a tape wound in the form of a coil. The hysteresis of V-I curves measured on short samples is suppressed by an external perpendicular magnetic field. The exact value of the field was dependent on sample type and form. In our sample, this field was similar to 15 mT. A model of electromagnetic field relaxation is used to explain qualitatively the effect of hysteresis and its suppression by the external magnetic field. (C) 2001 Elsevier Science B.V. All rights reserved.
