ARTIFICIAL PINNING CENTERS IN JELLY-ROLL PROCESSED NB CU COMPOSITES/

In order to clarify the mechanism concerning the enhancement of critic al current density (J(c)) due to artificial pinning centres (APC), nan ometer scale Nb/Cu multilayer composites have been prepared from Nb an d Cu foils by the jelly-roll process. The layer thickness of the speci men was chosen using a calculation based on the phenomenological Ginzb urg-Landau theory. The microstructure of the composite was investigate d by SEM. The J(c) and critical temperature (T-c) were measured at var ious magnetic fields. A remarkable increase in J(c) was found when the layer thickness was approximately the same scale as the vortex lattic e parameter. However, samples with thinner layers showed lower T-c val ues due to the proximity effect. (C) 1997 Elsevier Science Ltd.