History effects in low-field magnetoresistance of BPSSCO polycrystals

Abstract

Low-field (H < 40 G) magnetoresistance measurements have been made on Bi_1.6Pb_0.4Sr₂Ca₂Cu₃O_{1 0} polycrystals at several temperatures between 80 and 105 K. Considerable hysteresis in ρ^(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 ρ^(H) occurs for applied fields much lower than that at which dρ(H)/dH exhibits a discontinuity. In addition, we find that when the applied magnetic field (H_α ) is lowered from a maximum field, the effective intergranular field, H_eff, becomes zero for H_α >0, which gives rise to a minimum in ρ(H).