Lower Critical Field Determination in a Three-Dimensionally Textured Thick Rod of Float-Zone-Processed BiSrCaCuO: 2212/Ag

Abstract

The float-zone melting technique applied to polycrystalline rods of Bi-Sr-Ca-Cu-O (2212 phase) doped with 10 wt.% Ag has resulted in the growth of large-grained three-dimensionally textured rods in which the a,b planes of the crystallites (grains) were parallel to the growth direction and their c-axes were aligned perpendicular to it and nearly parallel to each other. On one such rod (12 mm long × 1.2 mm diam.) magnetization measurements of lower critical field, H_c1, were performed with the applied field directed parallel (Θ_∥ orientation) and perpendicular (Θ_⊥ orientation), respectively, to the c-axis. A new method of H_c1 determination was devised and employed — one that emphasizes the sought-after point of deviation from linearity of the initial magnetization line. The temperature dependence of H_c1 obtained in this way was of good precision for a bulk large-sample measurement, even revealing some novel structure in H_c1(T) in the Θ_∥ orientation of the kind that has already been observed in 2212 single crystals. The values of H_c1 obtained emphasized the pseudo-monocrystalline character of the rod; at 4.2 K H_c1(Θ_∥) was 320 Oe while H_c1(Θ_⊥) was about a factor of 40 smaller (~8 Oe).