UPt5−xAux: A heavy-fermion system with a selectablem/emph>

Measurements of the resistivity, susceptibility, and specific heat on ${\mathrm{UPt}}_{5\mathrm{-}\mathrm{x}}$ ${\mathrm{Au}}_{\mathrm{x}}$ (x≤3) and related compounds are reported. The reported heavy-fermion behavior in ${\mathrm{UPt}}_4$Au is confirmed by high-field measurements of the magnetization and specific heat. The high γ (∼800 mJ/mol ${\mathrm{K}}^2$) for ${\mathrm{UPt}}_4$Au is found to be extremely composition dependent, decreasing by 40% for a 2% change in the non-f-atom site occupation. The ${\mathrm{AuBe}}_5$ structure of ${\mathrm{UPt}}_5$ is found to be preserved up to ${\mathrm{UPt}}_2$ ${\mathrm{Au}}_3$. For x>1, the Wilson ratio climbs dramatically and the materials enter into a spin-glass-like magnetic state around 4 K.