Magnetic, Kondo and non-Fermi-liquid behaviour of U_1-xTh_xPd₂Al₃

Electrical resistivity ρ(T), magnetoresistance MR, magnetization M(T, B) and magnetic susceptibility χ(T, B) measurements at temperatures down to 25 mK and applied magnetic fields up to 14 T are presented for Th-diluted U_1-xTh_xPd₂Al₃ alloys. For U-rich alloys, antiferromagnetic order is observed and T_N varies slowly with the Th concentration in the region 0 ≤ x ≤ 0.2. From ρ(T) data we calculate a value of the energy gap Δ = 12 K in the spin-wave spectrum. In the U-rich concentration region a coherent Kondo description applies, but for alloys with 0.4 ≤ x ≤ 0.93 a non-Fermi-liquid (NFL) phase prevails. An approximately linear temperature dependence of ρ(T) is observed at low temperatures for about a decade in temperature, but deviation from this dependence occurs at the lowest temperatures. We show that the MR of the NFL alloys may be described in terms of the Coqblin-Schrieffer Hamiltonian, from which values of the single-ion characteristic Kondo temperature T_K ≈ 40 K are calculated. An applied magnetic field is shown to recover Fermi-liquid dynamics in both χ(T) and ρ(T). We give a description of the low-temperature magnetization M(T, B) in terms of a two-channel Kondo model.