New spin-fluctuation system:U0.5Th0.5Al3

Low-temperature measurements show a $T^3$(lnT/$T_{\mathrm{SF}}$) term in the specific heat of the pseudobinary compound ${\mathrm{U}}_{0.5}$ ${\mathrm{Th}}_{0.5}$ ${\mathrm{Al}}_3$. This is considered strong evidence for long-range ferromagnetic spin fluctuations. The specific heat γ is 360 mJ/[(mole U) ${\mathrm{K}}^2$] and χ(T→0)=9.6×${10}^{\mathrm{-}3}$ emu/(mole U). Except for a much less rapid decrease in resistance below 50 K than in ${\mathrm{UPt}}_3$, the resistance, susceptibility, and specific-heat data for the D$0_{19}$ structure ${\mathrm{U}}_{0.5}$ ${\mathrm{Th}}_{0.5}$ ${\mathrm{Al}}_3$ are very similar to those of the isostructural heavy-fermion superconductor ${\mathrm{UPt}}_3$. In addition to the poorer resistivity ratio, ${\mathrm{U}}_{0.5}$ ${\mathrm{Th}}_{0.5}$ ${\mathrm{Al}}_3$ has a significantly larger (∼50%) Wilson ratio than ${\mathrm{UPt}}_3$, explaining the lack of superconductivity down to 0.020 K.