Magnetoresistivity of R₂Rh₃Al₉ (R = Ce, La) and A₂Rh₃Ga₉ (A = U, Th)

The anomalous properties of Ce₂Rh₃Al₉ and of U₂Rh₃Ga₉ are investigated by magnetoresistivity (MR) measurements of these alloys and of their non-f electron counterparts La₂Rh₃Al₉ and Th₂Rh₃Ga₉ between room temperature and T = 1.4 K, and in magnetic fields up to 8 T. In U₂Rh₃Ga₉ there is a large, negative MR prevalent up to 80 K where the electrical resistivity ρ(T) reaches a maximum. The MR in Ce₂Rh₃Al₉ is small and negative below 8 K, then turns positive at the shoulder-like anomaly in ρ(T) and remains positive towards the peak seen in ρ(T ≃ 140 K). The analysis of MR(T,B) for U₂Rh₃Ga₉ in the paramagnetic Kondo-lattice region yields a Kondo temperature of T_K = 5.3(1) K which is of the same order as the magnetic ordering temperature.