Analysis of the magnetic relaxation in BiPbSrCaCuO high-T-C superconductors by means of an interaction model

The magnetic relaxation of cylindrical polycrystalline samples of BiPbSrCaC uO high-TC superconductors has been measured using an inductive technique n ear the transition temperature. The relaxation data are analyzed by means o f an interaction model based on the general theory of magnetic relaxation. This model assumes the existence of an effective energy barrier (U-eff) and considers thermal activation of the vortices over it. The pinning energy ( U-0) is reduced to the effective barrier U-eff=U-0-U-int by the energy asso ciated to the force of repulsion between vortices (U-int). In this work a l inear dependence between the interaction energy and the susceptibility has been used, but other dependencies can easily be introduced to account for t he observed nonlinearities of the U(J) curve. The model has been used to ex tract information of the relaxation of BiPbSrCaCuO samples at several magne tic fields and temperatures after switching off the field. A comparison wit h the results obtained by the Anderson-Kim model is also provided. (C) 1999 American Institute of Physics. [S0021-8979(99)16108-5].