Superconducting and magnetic properties of the heavy-fermion compounds UT2Al3(T=Ni,Pd)

The resistive upper critical field ${\mathit{H}}_{\mathit{c}2}$ as a function of temperature T has been determined for polycrystalline specimens of the isostructural antiferromagnetic heavy-fermion superconductors U${\mathit{T}}_2$ ${\mathrm{Al}}_3$ (T=Ni, Pd). The zero-temperature superconducting coherence lengths ${\xi }_0$=190 Å (77 Å) for T=Ni (Pd) have been estimated from the initial slope of ${\mathit{H}}_{\mathit{c}2}$(T), and analyses of previously reported specific-heat data yield an effective mass enhancement ${\mathit{m}}^{\mathrm{*}}$/${\mathit{m}}_{\mathit{e}}$∼40 (49) for T=Ni (Pd), where ${\mathit{m}}_{\mathit{e}}$ is the free-electron mass. High-precision measurements of the normal-state electrical resistivity reveal a broad anomaly below 4.6 K in ${\mathrm{UNi}}_2$ ${\mathrm{Al}}_3$, which correlates with the onset of U-moment antiferromagnetic ordering. In ${\mathrm{UPd}}_2$ ${\mathrm{Al}}_3$, the large electrical resistivity drop between ${\mathit{T}}_{\mathit{c}}$ and ${\mathit{T}}_{\mathit{N}}$≊15 K can be accurately described by an expression that is appropriate for an antiferromagnet with an energy gap Δ≊40 K and an additional ${\mathit{T}}^2$ term reflecting Fermi-liquid behavior.