TRANSITION FROM HEXAGONAL TO CUBIC STRUCTURE AND ENHANCED SPECIFIC-HEAT IN CEPT5-XAUX

In our attempt to replace platinum successively by gold in CePt5-xAu2, we have found that with increased Au content the initial hexagonal Ca Cu5 structure of CePt5 changes into the cubic AuBe5 structure for 1<x less than or equal to 3. Since this is the same lattice as in the heav y fermion system UPt4Au, with U replaced by Ce, we can now compare the role of the two different elements in this configuration. We have inv estigated the influence of the Au content on the low temperature speci fic heat and magnetic susceptibility, which both increase with increas ing Au content, and discuss to what extent this enhancement might be c reated by the electronic density of states or by magnetic entropy. Fur thermore, we have studied the transition from the U-based heavy fermio n system into the Ce-based system in U1-yCeyPt4Au.