Transport Barkhausen-like noise and flux-flow regime in Bi1.65Pb0.35Sr2Ca2Cu3O10+6 ceramic samples

We report on the detection of transport Barkhausen-like noise (TBN) in polycrystalline samples of Bi1.65Pb0.35Sr2Ca2Cu3O10+delta T = 77 K. Measurements of magnetization versus applied magnetic field performed in powder samples at the same temperature indicate that the grains have a Bean-like behavior. From this curve we were able to determine the first critical field of the grains H-clg similar to 80 Oe and the full penetration field of the grains H* similar to 135 Oe. Based on these results, the sample was subjected to an AC magnetic field with amplitude, B-max = 6 mT and frequency, f = 1 Hz in order to avoid the flux penetration within the grains. Then, by using the standard DC four-probe method, the transport Barkhausen-like noise was measured for several values of excitation current. The results reveal that, under certain conditions, a noise in the voltage signal of the sample is clearly identified and related to the transition of the sample to the flux-flow regime. By using the Fast Fourier Transform (FFT) method, the power spectrum of TBN data is calculated and exhibits an 1/f(2) frequency dependence, suggesting that the transition to the flux-flow regime in these materials is not a smooth process. (C) 2005 Elsevier B.V. All rights reserved.