Fig. 1. The variation of ;  with the magnetic "eld at low temperatures 5)¹)20 K for the AP and OR samples. * Corresponding author. Tel.: #30-1-65-22-872; fax: #30-1- 65-19-430. E-mail address: gkallias@ims.demokritos.gr (G. Kallias) Physica B 284}288 (2000) 807}808 Magnetic moment relaxation measurements in c-axis oriented bulk Bi  Sr  Ca  Cu  O  George Kallias*, Elias Moraitakis, Dimosthenis Stamopoulos, Dimitris Niarchos, Michael Pissas Institute of Materials Science, NCSR Demokritos, 153 10 Ag. Paraskevi, Athens, Greece Abstract We performed magnetic moment (m) relaxation measurements at low temperatures (5)¹)20 K) in two single phase, c-axis-oriented polycrystalline Bi  Pb  Sr  Ca  Cu  O  (2223) samples prepared under di!erent conditions with di!erent ¹  's. The m versus t data show a logarithmic relation and by "tting them the J  (H, ¹) and ;  (H, ¹) variation were extracted.  2000 Elsevier Science B.V. All rights reserved. Keywords: Bi-2223; Magnetic relaxation Magnetic relaxation measurements in high-temper- ature superconductors can give important information about the activation energy ;  and the critical current density J  that are determined by microscopic mecha- nisms of #ux dynamics and pinning. The magnetic phase diagram is extensively studied in Bi  Sr  CaCu  O  [1}4], whereas in 2223 due to the non-availability of high-quality single crystals the corresponding e!ort is much less [5,6]. In this paper we report preliminary magnetic moment relaxation measurements for two 2223 single phase, c- axis-oriented samples prepared under di!erent condi- tions. The samples can be considered as an oriented collection of platelet-like crystallites, with H  c. The "rst sample with ¹  "109 K (as-prepared, AP) is prepared with solid-state reaction in air. The second sample with ¹  "104 K (oxygen-reduced, OR sample) was prepared after annealing part of the AP sample in #owing Ar at 7003C. For the relaxation measurements, the sample was cooled in zero "eld, and then the "eld was increased to the desired value "eld and the data were collected after a 120 s interval. The m(t) data present a linear variation in semi-logarithmic plot for all temperatures (0)¹) 20 K) and applied magnetic "elds (0)H) 40 kOe). The measurements were performed in all cases below the irreversibility line for both samples [7]. The data were modelled using the relation m(t)" m  !m  ln(t/t  ), where m  "m  (k¹/;  ) and t  " 0.920j  da(k¹/;  )/ cE  , which holds for su$ciently strong non-linear E(J)J exp[!;(J)/k¹] character- istics in the case of a thin disk [8] with ;(J) described by the interpolation formula (;(J)"(;  /)[(J  /J)!1]) predicted in collective creep and vortex glass theory [9]. 0921-4526/00/$ - see front matter  2000 Elsevier Science B.V. All rights reserved. PII: S 0 9 2 1 - 4 5 2 6 ( 9 9 ) 0 2 1 0 6 - 7