Properties of Ba₂YCu₃O_7-δ filaments directionally solidified by the laser-heated floating zone technique

Textured and single-crystalline filaments of YBa₂YCu₃O_7-δ containing dispersions of ∼1 μm BaY₂CuO₅ particles were fabricated by the laser-heated floating zone technique. The volume fraction of the superconducting phase decreased linearly with increasing growth rate over the entire range investigated, from 1.1 to 8.33 μm/s. The effects on the critical current density (J_c) of grwoth rate (R), filament orientation with respect to applied magnetic field, and temperature were investigated by magnetization measurements. The samples were solidified with planar front, at velocities below 3.1 μm/s. J_c increased with growth rate in these samples, despite the observed decrease in the volume fraction of Ba₂YCu₃O_7-δ. The samples solidified with cellular or dendritic fronts at growth rates above about 3.1 μm/s. The critical current density of these samples decreased with increasing 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 10⁵ A/cm² at 77.3 K. A weak field dependence of J_c was observed in a single-crystalline filament at and below 50 K. For the same sample, magnetization J_c values close to 10⁶ A/cm² at 30 K and in excess of 3×10⁶ A/cm² at 4.2 K were measured with the applied field perpendicular to the sample axis. The magnetization of a single-crystalline sample measured in a perpendicular fild at different angles of rotation (θ) of the sample about its axis followed a dependence of the type ΔM = A + B |cosθ|.