Clean bulk YBaCuO superconductors doped by paramagnetic ions of Sm and Yb

Abstract

The recently developed clean cuprate technology was employed to study the effect of tiny amounts of paramagnetic Yb and Sm ions on electromagnetic properties of bulk YBaCuO. Small samples of about 1:5-1:5-0:5 mm3 were measured by vibrating sample magnetometer in the field range ±9 T and temperatures 30 K to 10 K in the non-superconducting tetragonal state and 300 K to 70 K in the orthorhombic, superconducting state. In the latter case, we observed the reversible paramagnetic moment above TC, similar as in the tetragonal state. Below TC an irreversible magnetic moment was observed from which critical current density, Jc, was evaluated using the extended Bean model. The effect of doping by Yb and Sm ions on Jc was studied and a correlation between Jc and the total paramagnetic moment was found. Both Jc(B) and the normalized pinning force density as a function of the reduced magnetic field were analyzed in terms of the classical model and discussed with respect to the material anisotropy, giving us at least a rough idea on the type of the effective pinning type and mechanism.