Magnetic behavior of the high T_c composite compound of Y₁Ba₂Cu₃O_7-δ in the superconducting phase

Detailed measurements of the magnetic properties in the superconducting state of a composite sample with approximately 35% Y₁Ba₂Cu₃O_7-δ and a T_c of 87K are compared with results on a corresponding single phase sample. The susceptibility is approximately linear in temperature below and near T_c indicating large magnetic field penetration near the transition. At low temperatures, a volume flux expulsion of 5% is found in lowest magnetic field, with H_c1 indicated to be 1.5kG. Magnetization loops are presented, showing hysteretic behavior even at 4.2K and 100G. At higher temperatures, the magnetization curves bear a striking resemblance to those for a large κ type II superconductor. The Curie susceptibility associated with spin in the non-superconducting phase remains unscreened below T_c in sharp contrast to the behavior of the rare earth 1-2-3 compounds, indicating that the magnetic flux percolates easily through the composite.