THE EFFECT OF ANISOTROPIC FLUX-PINNING MICROSTRUCTURE ON THE SAMPLE LENGTH DEPENDENCE OF THE MAGNETIZATION CRITICAL-CURRENT DENSITY IN NIOBIUM-TITANIUM SUPERCONDUCTORS
Cb. Nunes et al., THE EFFECT OF ANISOTROPIC FLUX-PINNING MICROSTRUCTURE ON THE SAMPLE LENGTH DEPENDENCE OF THE MAGNETIZATION CRITICAL-CURRENT DENSITY IN NIOBIUM-TITANIUM SUPERCONDUCTORS, Journal of applied physics, 80(3), 1996, pp. 1647-1651
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.