Suppression of spin fluctuations by alloying in UPt3

In order to investigate the normal state spin fluctuation behavior of UPt₃, we have measured the low temperature resistivity and specific heat C of U(Pt_0.8Pd_0.2)₃, which we find to be close to the phase stability boundary for the hexagonal UPt₃ structure. The evidence for spin fluctuations observed in UPt₃, aT ³ ln (T/T _SF) upturn inC/T below 10 K, is totally suppressed in U(Pt_0.8Pd_0.2)₃, and the value, proportional to the dressed density of states, is decreased by 50% compared to pure UPt₃. This extreme sensitivity to substitution by isoelectronic Pd for Pt indicates that the spin fluctuations in UPt₃ depend critically on the hybridization of the U electrons, U-U separation equal to 4.2 Å, with the electrons of the intervening atoms.