Transport properties in the URu_1-xPd_xGa system

The effect of substitutions in the URu_1-xPd_xGa system has been investigated by means of electrical resistivity and magnetoresistivity measurements. The substitutions of Pd for Ru have been found to (i) suppress a Kondo behaviour at high temperatures, (ii) produce magnetic order and (iii) induce a Kondo-like minimum in the electrical resistivity at low temperatures. We analysed the low-temperature part of the electrical resistivity by considering electron scattering by impurities, by spin-wave excitations and originating from a Kondo effect. Samples with 0 ≤ x ≤ 0.3 exhibit incoherent Kondo behaviour above about 100 K, while for the 0.4 ≤ x ≤ 0.8 compositions a broad maximum appears in the resistivity around 150-180 K, presumably due to a combination of the Kondo and crystal-field effects. The magnetoresistivity results support the earlier proposal derived from the magnetic studies of the URu_1-xPd_xGa system in which a magnetic phase transition from paramagnetic to ferromagnetic and finally to an antiferromagnetic/ferrimagnetic state takes place. A marked difference was found in the magnetoresistivity data for the x = 0.2, 0.6 and 0.8 samples, reflecting a variety of magnetic structures which appear in these compounds.