THE EFFECT OF ANISOTROPIC FLUX-PINNING MICROSTRUCTURE ON THE SAMPLE LENGTH DEPENDENCE OF THE MAGNETIZATION CRITICAL-CURRENT DENSITY IN NIOBIUM-TITANIUM SUPERCONDUCTORS

Magnetization measurements of the critical current density J(c) in Nb 47 wt % Ti with Nb artificial pinning centers revealed that the shape and magnitude of the field dependent magnetization hysteresis Delta M( H) was a strong function of the sample length and that Delta M(H) for short wire samples was up to six times smaller than for long wires. Th is is caused by the strong anisotropy of the critical current density J(c). The magnitude of J(c) flowing perpendicular to the wire axis J, was deduced to be 50-175 times smaller than the longitudinal current d ensity J(parallel to). The source of the anisotropy lies in the anisot ropic flux pinning microstructure of the wires. When the magnetization current crosses perpendicular to the filament axis at each end of the wire, the Lorentz force is parallel to the pinning center axis. The p inning force is weak in this direction and J(perpendicular to) is corr espondingly small. The technologically important critical current dens ity is the longitudinal current density J(parallel to). It can be extr acted from magnetization measurements only in the case of large length to diameter filaments, as is quantitatively analyzed here. (C) 1996 A merican Institute of Physics.