Doping Effect of Fe-Ni Alloy Particles on Flux Pinning in Gd-Ba-Cu-O Bulk Superconductor

Enhancement of the critical current density (J(C)) and trapped flux density (B-T) of bulk high-temperature superconductor are essential for large-scale applications. Introducing artificial pinning centers into the superconducting matrix has been proved to be an effective way to enhance J(C) and B-T. It has been suggested that the ferromagnetic particles doping may provide higher pinning potential. The doping effects of Fe-B soft magnetic particles for GdBa2Cu3O7-sigma (Gd123) bulk were reported previously. In the present work, we reported the improvements in both J(C) and B-T of Gd123 bulk doped by Fe-Ni alloy particles. To make sure a uniform distribution of the dopant, Fe-Ni alloy particles, with amount varied from 0 to 20 mol%, were initially added to prepare Gd123 precursor powders for the bulk processing. X-ray diffraction showed a tetragonal-orthorhombic transition of Gd123 crystal structure with increasing doping amount. The in-field J(C) was greatly enhanced by the Fe-Ni particles doping and the optimal doping amount was found to be 0.5 mol%. The microstructure of the bulk samples were also investigated by scanning electron microscopy. The great improvement of trapped flux by Fe-Ni doping was considered to be benefit for practical applications.