Evidence of field-induced non-Fermi-liquid behavior in YbCu5-xAlx compounds

We measured the specific heat, magnetic susceptibility and electrical resis tivity of YbCu5-xAlx in magnetic fields up to 13 T. Between x = 1.6 and 2 t hese compounds order antiferromagnetically with a Neel-temperature between 0.25 and 2 K, respectively. In high fields the antiferromagnetic transition is suppressed and a crossover to Fermi-liquid behavior occurs. Ar a critic al field B-cr, non-Fermi-liquid (nFl) behavior is found which is characteri zed by a - log T contribution to the specific heat CIT down to 300 mK as we ll as deviations from. T-2 behavior in the electrical resistivity. The magn etic susceptibility measured in B-cr is proportional to 1 -a root T below 6 K. A scaling analysis of the specific heat and magnetization data obtained in higher fields (B > B-cr) points to collective effects responsible for t he field-induced nFl behavior. This is the first system besides CeCu6-xAgx where field-induced nFl behavior is found. (C) 2000 Elsevier Science B.V. A ll rights reserved.