Superconductivity in Niobium Containing Ferromagnetic Gadolinium or Paramagnetic Yttrium Dispersions

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Abstract
Gadolinium and yttrium dispersions were prepared in pure niobium by solidification from the melt; the size, shape, and distribution of the particles were determined metallographically. The superconducting critical temperature and critical field of niobium were unaltered by the presence of the dispersions indicating that neither gadolinium nor yttrium have measurable solubility in solid niobium. Both gadolinium and yttrium dispersions produced large hysteresis in magnetization and large critical current densities. The degree of magnetic hysteresis produced in niobium by these dispersions has only been exceeded in niobium by fast neutron irradiation. Ferromagnetic gadolinium and weakly paramagnetic yttrium appear equally effective as flux pins. It is suggested that the nature of the particle superconducting matrix interface is more important for flux pinning than the bulk magnetic properties of the dispersed phases.