Critical current density and flux pinning in Ho-doped melt-processed YBa₂Cu₃O_y

We fabricated highly textured Y_1-xHo_xBa₂Cu₃O_y (x=0, 0.2, 0.4, and 0.6) bulk samples by a "powder melting process" method under identical conditions and investigated their critical current densities and flux pinning behavior with a superconducting quantum interference device magnetometer. The dependence of J_c on the magnetic field, estimated by the Bean model, is studied. The results indicate that J_c drops with the magnetic field according to a power law J_c∝H^-n (n<0.5), which implies that the J_c value of these samples is controlled by the flux pinning rather weak links. It is found that J_c and flux pinning can be significantly improved by Ho substitution for Y in Y-based superconductors. The reduction of the size of Y₂BaCuO₅ particles, stress-field pinning, and magnetic pinning created by the Ho addition are considered to be responsible for the increase in J_c and flux pinning.