INVESTIGATION OF COLLECTIVE CREEP IN YBACUO

Time dependent decay of the magnetic moment M(t) and magnetization mea surements were used to study flux creep in melt textured YBaCuO sample s. From both measurements voltage current characteristics were reconst ructed between 10(-1) and 10(-7) muV/cm up to the region of the irreve rsibility field. The exponent mu of the power law dependence of the pi nning barrier was obtained from M(t) using the time constant of the in itial stage of relaxation and from E(j) analysis. The current dependen ce of mu shows a maximum, negative values on both sides as well as the field dependence are not in agreement with theoretical predictions.