Effects of strong magnetic fluctuations on the transport behavior of pyrochlore ruthenates near the metal-insulator phase boundary

Transport and magnetic properties of pyrochlore ruthenates R2-xBixRu2O7 (R=Sm and Eu), which exhibit the Mott insulator to metal transition with increasing x, have been studied. The electrical resistivity rho and the Hall coefficient R-H are found to strongly couple to the change of the magnetic state, or the transition to the spin-glass state which takes place at temperature T = T-G. Near the metal-insulator phase boundary, R-H above T-G increases rather rapidly with decreasing T even in the metallic phase, and the Hall angle theta(H) follows a simple relation, cot theta(H) proportional to a + bT(2), over the wide T-range. At T = T-G, R-H has a peak and it decreases with decreasing T. These results indicate that strong spin fluctuations above T-G induce the anomalous T-dependence of R-H in the present magnetically frustrated three-dimensional system and R-H decreases as the spin freezing proceeds.