ANISOTROPIC FLUX-PINNING IN YBA2CU3O7-DELTA SINGLE-CRYSTALS - THE INFLUENCE OF DEFECT SIZE AND DENSITY AS DETERMINED FROM NEUTRON-IRRADIATION

Substantial information about the pinning of flux lines in YBa2Cu3O7-d elta single crystals can be gained from an interpretation of the chang es in the critical temperature T-c and the magnetization loops after n eutron irradiation. After annealing the irradiated samples, a well-def ined defect structure prevails. A careful interpretation of the data a llows one to arrive at conclusions on the unknown defect structure and flux pinning before irradiation and annealing. The variation of T-c i s explained by the mobility of smaller defects and their interaction w ith the radiation-induced defect cascades. The results on the critical current densities lead to the proposition that strong pinning prevail s in most YBa2Cu3O7-delta single crystals, even in the as-grown state. Current theories for the summation of the elementary pinning forces a re tested, but cannot consistently explain the experimentally observed macroscopic pinning force. If the field is applied perpendicular to t he crystallographic c axis, a significant influence of the smaller def ects on the anisotropy of the crystal can be deduced from an analysis of the critical current densities. [S0163-1829(98)02817-3].