ONSET OF MAGNETIC ORDER IN YBCU5-XALX

Spectroscopic, magnetic, thermal, and transport measurements under pre ssure are presented which were performed on YbCu5-xAlx intermetallics. The substitution of Cu by Al in YbCu5 drives the system from an almos t divalent behavior of the Yb ion in YbCu5 to a trivalent state in YbC u3Al2. A compensation between the normal thermal expansion and a valen ce-driven contraction was found for YbCu4Al. Antiferromagnetic order s ets in for x>1.5, where an increasing Al content causes both a growing transition temperature and rising saturation moments reaching 2 K and about 2.1 mu(B), respectively, for x=2. At the critical concentration (x approximate to 1.5) the possibility of a non-Fermi-liquid state is analyzed together with its tuning by pressure.