Heavy-fermion behavior and spin-glass freezing in Si-stabilized amorphous alloys based on UPt3

U-Pt-Si and U-(Pt, Pd)-Si alloys have been prepared in the amorphous state by splat-cooling. The average nearest-neighbor distance is the same as the U-Pt distance in UPt3. The low-temperature behavior of these alloys (with composition (U0.25Pt0.75)1-xSx, x=0.18, 0.20, 0.25; and (U0.25(Pt1-yPdy)0.75)0.8Si0.2, y=0.05 and 0.1) has been studied by specific heat C, magnetization and resistivity measurements in the temperature range 1.5 K to 20 K and for magnetic fields up to 6 T. Some samples were investigated down to 0.1 K and the specific heat for one sample was measured in fields up to 22 T. With gamma0 = C/T{\textbackslash}T--{\textgreater}0 between 0.25 and 0.35 J/mole UK2, the alloys can be classified as heavy-fermion materials. As opposed to UPt3, the alloys exhibit spin-glass behavior with a concomitant decrease of gamma0. The magnetization exhibits typical spin-glass features (e.g., an irreversibility line). An inverse relationship between gamma0 and T(max) (temperature of C/T maximum which is proportional to the spin-glass freezing temperature), irrespective of the Pd content, is observed. The behavior can be qualitatively described by a coexistence of heavy-fermion behavior and spin-glass freezing.