PROPERTIES OF BA2YCU3O7-DELTA FILAMENTS DIRECTIONALLY SOLIDIFIED BY THE LASER-HEATED FLOATING-ZONE TECHNIQUE

Textured and single-crystalline filaments of Ba2YCu3O7-delta containin g dispersions of approximately 1 mum BaY2CuO5 particles were fabricate d by the laser-heated floating zone technique. The volume fraction of the superconducting phase decreased linearly with increasing growth ra te over the entire range investigated, from 1.1 to 8.33 mum/s. The eff ects on the critical current density (J(c)) of growth rate (R), filame nt orientation with respect to the applied magnetic field, and tempera ture were investigated by magnetization measurements. The samples were solidified with planar front, at velocities below 3.1 mum/s. J(c) inc reased with growth rate in these samples, despite the observed decreas e in the volume fraction of Ba2YCu3O7-delta. The samples solidified wi th cellular or dendritic fronts at growth rates above about 3.1 mum/s. The critical current density of these samples decreased with increasi n growth rate, as expected. Magnetization measurements performed in a field of 0.05 T applied perpendicular to the sample axis and transport measurements in self-field resulted in J(c) values larger than 10(5) A/cm2 at 77.3 K. A weak field dependence of J(c) was observed in a sin gle-crystalline filament at and below 50 K. For the same sample, magne tization J(c) values close to 10(6) A/cm2 at 30 K and in excess of 3 x 10(6) A/cm2 at 4.2 K were measured with the applied field perpendicul ar to the sample axis. The magnetization of a single-crystalline sampl e measured in a perpendicular field at different angles of rotation (t heta) of the sample about its axis followed a dependence of the type D ELTAM = A + B\cos theta\.