METAMAGNETIC TRANSITIONS IN THE HEAVY-FERMION SYSTEM U(PT, PD)3

High-field magnetisation measurements on single-crystalline samples of the heavy-fermion system U(Pt(1-x)Pd(x))3, reveal metamagnetic-type of transitions in the liquid-helium temperature region for Pd concentrations with x-values below 0.1 and field directions perpendicular to the hexagonal axis. These transitions are considered to reflect the suppression of short-range antiferromagnetic inter-site correlations and have further been investigated in specific-heat experiments with applied magnetic fields up to 24.5 T. For the compound with a Pd content equivalent with x = 0.05, in addition long-range antiferromagnetic order is found below 6 K. This long-range order is signalled in the specific heat at zero field by a sharp peak near 6 K. For magnetic fields applied perpendicular to the hexagonal axis, this peak shifts to lower temperatures with increasing field and seems to disappaer for field values around 12 T, the field where the metamagnetic transition in the magnetisation experiments is observed. By combining the magnetisation and specific-heat data, magnetic phase diagrams have been constructed for the studied compounds.