MAGNETISM AND SUPERCONDUCTIVITY OF THE U(PT,PD)(3) SYSTEM

The superconducting phase diagram of UPt3 has been studied by a variet y of techniques, all leading to three different phases in the B-T plan e that meet the normal phase in a tetracritical point. Superconductivi ty has been reported to coexist with small-moment antiferromagnetism. The effects of substitutions on either the U site or the Pt site on th e superconducting transition have been addressed in several studies. P d substitutions for Pt play a particular role since the zero-field spl itting between two superconducting phases increases from about 60 mK f or pure UPt3 to about 120 mK for the 0.2 at % Pd alloy. On further inc reasing the Pd content, superconductivity is suppressed above 0.5 at % Pd, whereas between 2 and 10 at % Pd long-range antiferromagnetic ord er is observed with values of the uranium moment up to 0.6 mu(B). The relevant questions in these Pd substitution studies are: by which mech anism is the splitting between the two zero-field superconducting phas es enhanced and, secondly, in which way does the small-moment antiferr omagnetism evolve into the large-moment antiferromagnetic order at hig her Pd concentrations. In this contribution, the salient features are reviewed with respect to the occurrence of magnetic order and supercon ductivity in the pseudo-binary system or U(Pt, Pd), alloys, with an em phasis on dilatation experiments.