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.