A comparative study of irreversible magnetisation and pinning force density in (RE) Ba2Cu3O7-δ and some other high-Tc compounds in view of a novel scaling scheme

We examined an extended set of experimental data on scaling of the field dependencies of the critical current density j(s)(B) and/or the related pinning force density F(B) as found in literature for various high-T-c single crystals, mainly (RE)Ba2Cu3O7-delta (RE = rare earth), exhibiting the fishtail effect. The j(s)(B) and/or F(B) curves, normalised with respect to the corresponding (fishtail) maximum, are shown to obey the functional dependencies j(sc)(b) = b(m)exp[(m/n)(1 - b(n))] and f(b(f))= b(f)(m+1)exp{[(m + 1)/m](1 - b(f)(n))} where b and b(f), are the applied field values normalised with respect to position of the corresponding (fishtail) maximum, and j(sc) and f are the normalised values of the critical current density, and pinning force density, respectively. A possible link between the presented phenomenological scaling scheme and the theory of collective pinning is discussed. Most of the analyzed data could be well fitted with m set equal to 1 and n left as the only free parameter. n varied from 0.5 to 3.95 but most values fell into the interval (1,2). We point out that the value n = 3/2 in the middle of this interval is predicted by the collective pinning theory for the small bundle pinning regime. (C) 1997 Elsevier Science B.V.