Basic pinning interaction between flux lines and superconducting precipitates

Using an improved technique for the direct recording of flux density distribution in the gap between two identical superconductors, the flux density gradients in the model system PbNa were investigated. Depending on the annealing procedure superconducting precipitates of the Pb3Na-phase of different size and shape are formed. The present results refer to spherical precipitates [phi=420 A, Nsub(V)=3.1015cm-3 annealing for 1 hour at 1220C] and to cylindrical precipitates (phi=720A, 1=3900A, Nsub(V)=7.1.1013cm-3, annealing for 16.1 h at 1220C), which align in the (100)-directions and present also an essentially spherical surface to the flux lines, if the (111)-crystal direction is parallel to the external field. (Auth.)