Small magnetic hysteresis and anisotropy of textured high-temperature superconductor Bi2223

In materials based on high-temperature superconductors (HTSC) with a pronounced granular structure, along with the main superconducting subsystem – HTSC granules, an additional subsystem with weakened superconducting properties appears, formed by intergranular boundaries (Josephson junctions). This “weak” superconducting subsystem manifests itself as a “small” magnetic hysteresis existing in a certain range of sufficiently weak external fields. In this paper, we study the small magnetic hysteresis of a textured sample of Bi$_{1.8}$Pb$_{0.3}$Sr$_{1.9}$Ca$_2$Cu$_3$O$_x$ (Bi2223), in which the plate-like Bi2223 crystallites are predominantly oriented relative to the crystallographic c-axis. It is found that the range of existence of a small hysteresis differs for the directions of the external magnetic field $\mathbf{H}$ parallel and perpendicular to the orientation of the $c$-axis of the crystallites. To explain this experimental fact, the influence of magnetic moments of Bi2223 crystallites on the effective field in the intercrystallite boundaries is considered. The magnetic induction lines from the magnetic moments of superconducting crystallites are closed through the intercrystallite boundaries, and at the orientation $\mathbf{H}\perp c$ a partial compensation of the field induced by neighboring crystallites occurs due to their misalignment. This leads to the fact that the influence of the main superconducting subsystem (Bi2223 crystallites) on the intercrystallite boundary subsystem is smaller, and the range of the external field in which a small hysteresis exists is larger at $\mathbf{H}\perp c$ than at $\mathbf{H}\parallel c$.