A comparative study of irreversible magnetisation and pinning force density in (RE) Ba 2Cu 3O 7−δ and some other high- Tc compounds in view of a novel scaling scheme

Abstract

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)Ba 2Cu 3O 7−δ (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 ƒ(b f ) = b f m+1 exp{[(m + 1)/m](1 − b f n)} where b and b f, are the applied field normalised with respect to position of the corresponding (fishtail) maximum, and j sc and ƒ 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.