Anomalous transport behavior in geometrically frustrated system R2-xBixRu2O7 (R = rare earth, Y)

We have studied transport and magnetic properties of ruthenium pyrochlore o xides R2-xBixRu2O7 (R = rare earth, Y), which exhibit the Mott insulator to metal transition with increasing I. The spin-glass transition can be obser ved basically in the insulating x-region, which may be due to the freezing of Ru spins. Transport quantities, the electrical resistivity rho, the Hall coefficient R-H and the thermoelectric power S are found to be strongly af fected by the spin-glass transition. Furthermore, near the metal-insulator phase boundary, R-H increases rather rapidly with decreasing temperature an d the Hall angle theta (H) obeys the relation cot theta (H) = a + bT(2) in the paramagnetic state. These results suggest that there exist strong spin fluctuations in the metallic state of R2-xBixRu2O7, which is suppressed as the spin freezing proceeds. (C) 2000 Elsevier Science Ltd. All rights reser ved.