HISTORY EFFECTS IN LOW-FIELD MAGNETORESISTANCE OF BPSSCO POLYCRYSTALS

Low-field (H < 40 G) magnetoresistance measurements have been made on Bi1.6Pb0.4Sr2Ca2CU3O10 polycrystals at several temperatures between 80 and 105 K. Considerable hysteresis in p(H) is found in a zero-field-cooled sample when the applied field is increased from 0 to a maximum value and then lowered back to 0 at all temperatures. The observation of hysteresis is taken as an evidence for field trapping in the grains. We show that the hysteresis in p(H) occurs for applied fields much lower than that at which dp(H)/dH exhibits a discontinuity. In addition, we find that when the applied magnetic field (H-a) is lowered from a maximum field, the effective intergranular field, H-eff, becomeszero for H-a < 0, which gives rise to a minimum in p(H).