MODELING OF M-H LOOP ANOMALIES IN SYNERGISTICALLY PINNED, HETEROGENEOUS, COMPOSITE SUPERCONDUCTORS

A model which describes a low-field anomaly in the M-H loops of compos ite superconductors has been developed. Corresponding calculations wer e applied to the anomaly as it occurs in a composite system composed o f NbTi filaments in a proximity-effect coupled matrix. The use of this system has allowed a very clear and unambiguous separation of the mag netization contributions of 'strong' (S) and 'weak' (W) superconductin g elements. The low field anomaly, in the form of a difference between the shielding- and trapping-branch critical current densities (J(c)) for the W-phase, and hence an asymmetric magnetization loop, takes pla ce when the magnetization currents in the W-phase become influenced by the density of trapped flux in the S-phase. Comparison of theory and experiment gives values for the W-region J(c) which are in general agr eement with those derived from the results of more conventional measur ements. (C) 1998 Published by Elsevier Science B.V. All rights reserve d.