MAGNETIC CORRELATIONS AND MAGNETIC-ORDERING IN CECU6-XAUX SINGLE-CRYSTALS

While CeCu6 does not show long-range magnetic order, the intersite magnetic correlations in CeCu6 developing below 1 K are destroyed in a magnetic field of B almost-equal-to 2 T as evidenced by a distinct maximum in the derivative of the magnetization M, dM/dB versus B, which vanishes for T > 0.6 K. This metamagnetic-like transition thus appears to be a common feature of heavy-fermion systems without long-range magnetic order. CeCu6-xAux alloys show long-range antiferromagnetic order for x > 0.1, e.g., T(N) = 0.48 K for x = 0.3 and 0.95 K for x = 0.5. The increase in the Ce-Ce distance with x stabilizes the Ce moments against formation of local Kondo singlets. The alloys have a similar easy-axis anisotropy as pure CeCu6. T(N) is suppressed strongly for B parallel-to c, while it hardly changes for B parallel-to b. Likewise, the reduction of the specific heat C below T(N) shows the same directional dependence. Even for x = 0.5, the Kondo compensation affects the magnetization (M congruent-to 1 mu(B)/Ce atom in 6 T at 0. 15 K) and the specific heat (C/T congruent-to 2.3 J/mol K2 for T --> 0).