ANOMALOUS SUPPRESSION OF T-C AND MODERATE HEAVY-FERMION BEHAVIOR IN YBNI2B2C

We have synthesized single phase material YbNi2B2C. Results of our X-r ay diffraction and L(III)-edge studies are consistent with (nearly) tr ivalent state of Yb-ions in this material. Superconductivity is not ob served down to 2 K in our resistivity and magnetic susceptibility stud ies. This is anomalous as, with Yb-ions in 3+ state, one expects T-C s imilar to 12K in this material on the basis of the systematic of T-C i n other magnetic superconductors belonging to the series RNi(2)B(2)C ( R, a rare earth ion). Resistivity is relatively temperature independen t in the temperature range 50K-300K. However, below 50K there is a lar ge reduction of resistivity. The Sommerfeld coefficient, gamma, obtain ed from the heat capacity data in the temperature range 12K-25K, is si milar to 200 mJ/mol.K-2 which suggests the formation of a moderately h eavy fermion state in YbNi2B2C at low temperatures. Suppression of sup erconductivity constitutes an independent evidence of anomalous state of Yb-ions in YbNi2B2C Copyright (C) 1996 Published by Elsevier Scienc e Ltd