Magnetization analysis of high Tc superconductor by new critical state model with Meq

New critical state model was proposed using empirical reversible (equilibrium) magnetization M-eq to analyze the magnetization curves of type-II high T-c superconductor. The M-eq and (dM(eq)/dH) were assumed to be continuous at H-cl and larger than -1 above H-cl, respectively. In our KI model, J(c) of Kim's model was adopted. The internal flux density B-int(x, H) were derived from mu (0)J(c) = -deltaB(int)/deltax, and the expressions of M were given by (B-int/mu (0)) - H, where ( )meant spatial average. Analyzing the magnetization of sintered Bi2223 at 50 K by KI model, the internal penetration flux density B-eq(*) of 40 mT and specific constant of B-0 = 58 mT were obtained, together with the penetration field of 75 mT, irreversible field of 2 T and lower critical field smaller than 2 mT. Additionally, about 9% superconductive volume fraction was also estimated for this system at 50 K. (C) 2001 Elsevier Science B.V. All rights reserved.