ESTIMATION OF AC LOSSES OF POLYCRYSTALLINE YBCO BY TWO DIFFERENT METHODS

For evaluation of ac losses of polycrystalline YBa2Cu3Oy, ac transport and magnetization techniques were employed. As alternating currents were passed through a cylindrically sintered specimen, effectively resistive voltages were detected by means of a lock-in amplifier, which were shown to be linked with ac losses of the specimen. On the other hand, the field dependence of magnetically estimated ac losses for a small chip, synthesized in the same manner, exhibited a plateau region beginning at several tens of oersteds. This field was found to be equal to the self-induced magnetic field created by the dc critical current of the cylinder specimen and could be attributed to the grain decoupling field. Below this field (or Ic (dc)), the above two methods provided almost equivalent ac losses, which also semiquantitatively agreed with theoretical estimation using Bean's critical state model.