Magnetism and superconductivity of the U(Pt,Pd)3 system

The superconducting phase diagram of UPt3 has been studied by a variety of techniques, all leading to three different phases in the B-T plane that meet the normal phase in a tetracritical point. Superconductivity has been reported to coexist with small-moment antiferromagnetism. The effects of substitutions on either the U site or the Pt site on the superconducting transition have been addressed in several studies. Pd substitutions for Pt play a particular role since the zero-field splitting between two superconducting phases increases from about 60 mK for pure UPt3 to about 120 mK for the 0.2 at% Pd alloy. On further increasing the Pd content, superconductivity is suppressed above 0.5 at% Pd, whereas between 2 and 10 at% Pd long-range antiferromagnetic order is observed with values of the uranium moment up to 0.6μB. The relevant questions in these Pd substitution studies are: by which mechanism is the splitting between the two zero-field superconducting phases enhanced and, secondly, in which way does the small-moment antiferromagnetism evolve into the large-moment antiferromagnetic order at higher Pd concentrations. In this contribution, the salient features are reviewed with respect to the occurrence of magnetic order and superconductivity in the pseudo-binary system or U(Pt,Pd)3 alloys, with an emphasis on dilatation experiments. (orig.)