Large magnetic hysteresis in a melt-textured Y-Ba-Cu-O superconductor

Melt-textured YBa₂Cu₃O_7-δ superconductor with a long and well-aligned grain structure is shown to exhibit magnetic hysteresis at 77 K which is the largest ever reported for bulk polycrystalline Y-Ba-Cu-O. The large ΔM resulted in a magnet-like behavior as well as a strong suspension phenomenon. It is shown, contrary to the previous reports, that the suspension behavior observed in Y-Ba-Cu-O is a generic consequence of large grain size, and not due to the presence of Ag oxide or Ag particles. There appears to be no substantial enhancement in flux pinning and J_c by these particles. Comparisons of magnetization behavior in various YBa₂Cu₃O_7-δ samples (polycrystals, silver-oxide doped, melt-textured, and single crystals) indicated that for applied fields substantially larger than H_c1 the current flow that gives rise to the observed magnetization is intragranular. The pinning force and hence the critical current is roughly the same [J _c (magn)∼10⁴ A/cm²] within a factor of ∼2 regardless of grain size, grain boundary configuration, presence of second phase particles, or increased dislocation and twin densities.