Critical current density and related microstructure of textured YBaCuO rods produced by a melt growth process

Textured YBaCuO rods have been grown using a moving thermal gradient method. Electrical resistivity and precise AC magnetic susceptibility data are presented for the samples. Fine structure in the imaginary part of the susceptibility plots is related to features of the microstructure. Following generalization of the Beam critical state model, the authors calculate the flux profile and penetration depth, and deduce the critical current density. They also give values for the activation energy in the flux creep model. It is shown that the critical current density increases logarithmically with frequency, as expected, but that care is needed when comparing values of J_c obtained by different methods.