Onset of magnetism and Fermi-liquid instabilities in Yb compounds

YbCu5-xAlx provides the possibility to tune ground stare properties by a ch ange of the valence due to the Cu/AI substitution. by pressure as well as b y the application of a magnetic field. The former originates long-range mag netic order for x > 1.5 and at the critical concentration x(cr) approximate to 1.5 non-Fermi-liquid (NFL) properties are obvious, e.g., from a - In T contribution to the specific heat. The latter causes that antiferromagnetic order can be suppressed (x = 1.6 and x = 1.7) and at a critical magnetic f ield H-c NFL becomes evident while for H much greater than H-c a Fermi-liqu id ground state is recovered. (C) 2000 Elsevier Science B.V. All rights res erved.