MAGNETIZATION, UPPER CRITICAL-FIELD, AND ISOTROPY IN SINGLE-CRYSTALS YNI2B2C

Magnetization studies for single crystal YNi2B2C have been carried out in order to look for anisotropy in the upper critical field, H-c2. Ma gnetization vs. temperature curves are reversible to a few percent ove r a wide portion of the field-temperature (H-T) plane and are nearly l inear as predicted by Ginzburg-Landau theory. Values of H-c2 derived f rom a linear extrapolation of M vs. T plots for H parallel to the c-ax is and for H parallel to the ab-plane are the same within errors and h ence the samples are very isotropic. Two irregularities for these samp les are that the slope of the M vs. T curves decreases with increasing field and that the H-c2 vs. T curve may have a small positive curvatu re. Both of these features are contrary to the expectations of Ginzbur g-Laudau theory.