Oneset of magnetism and Fermi-liquid instabilities in Yb compounds

YbCu5-xAlx provides the possibility to tune ground stare properties by a change of the valence due to the Cu/AI substitution. by pressure as well as by the application of a magnetic field. The former originates long-range magnetic 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 field H-c NFL becomes evident while for H much greater than H-c a Fermi-liquid ground state is recovered