Modification of the fermi-surface instability in UPt(3) by Th substitution.

The magnetic susceptibility, specific heat, and electrical resistance of U(1-x)Th(x)Pt(3) have been studied for x between 0.01 and 0.10 at temperatures between 1.5 and 20K. In addition to the well known heavy-Fermion behavior, at 6.5K a Fermi-surface instability very similar to a spin--density-wave formation is observed and it is concluded that the superconducting ground state in UPt(3) is sensitive to Fermi surface details, which are modified by doping-induced strains.