Critical currents and relaxation in Bi-based ceramic superconductors

✍ Scribed by A.A. Zhukov; D.A. Komarkov; J. Mirkovic

• Publisher: Elsevier Science
• Year: 1992
• Tongue: English
• Weight: 423 KB
• Volume: 32
• Category: Article
• ISSN: 0011-2275
• DOI: 10.1016/0011-2275(92)90027-8

✦ Synopsis

The temperature and magnetic field dependences of inter-(i J) and intragrain (jc G) critical current densities obtained from magnetic measurements, as well as the relaxation of the intragrain magnetization, were studied on Bi-based ceramics. The best fitting for jJ is given byj J (B) = G(T)/(1 + B2/B 2) with the G(T) and Bo(T) dependences being close to linear. The magnetic field behaviour of jc 6 fits the exponential law j~(B) = jG(T) exp(-B/ B* (T)) with nearly exponential jGc(T) and B* (T). Values of j G at intermediate temperatures (-105 A cm-2) are an order of magnitude higher than in perfect single crystals, though at T~ 0they are close (-106 A cm-2). At T = 20 KjG(T) shows a kink accompanied by a drop in the normalized relaxation rate d(InM)/d(Int) that was previously observed in Bi single crystals and was related to the transition from a low to a high temperature pinning mechanism. The hysteretic and time-dependent transport critical current jc tr was measured at T = 77 K. The relaxation rate of jtc' exhibits complex, hysteretic behaviour in magnetic fields with the virgin jctr(H) curve showing no relaxation up to fields of 1 O00e.