Modification of the Fermi-Surface Instability in UPt3by Th Substitution

The magnetic susceptibility, specific heat, and electrical resistance of ${\mathrm{U}}_{1-x}{\mathrm{Th}}_x{\mathrm{Pt}}_3$ have been studied for $x$ between 0.01 and 0.10 at temperatures between 1.5 and 20 K. In addition to the well known heavy-fermion behavior, at 6.5 K a Fermi-surface instability is observed and it is concluded that the superconducting ground state in U${\mathrm{Pt}}_3$ is replaced by a spin-density wave. This result demonstrates the delicate balance between superconductivity and magnetism in U${\mathrm{Pt}}_3$.