ANISOTROPIC UPPER CRITICAL-FIELD OF LUNI2B2C

The upper critical field, H-c2, Of LuNi2B2C has been determined from t he temperature dependence of the magnetization. A temperature dependen t anisotropy within the basal plane which decreases from a value of 1. 1 at 4.5 K to a value of 1.0 at T-c and an almost temperature independ ent out-of-plane anisotropy have been observed. Near T-c the upper cri tical field along all directions shows a strong upward curvature. Thes e features of H-c2 can be explained quantitatively using a nonlocal ex tension of the Ginzburg-Landau equations. The Fermi velocity averages determined from these measurements and those obtained in band structur e calculations are in good agreement.