Giant Magnetoresistance Effect in the Metal-Insulator Transition of Pyrochlore Oxide Nd2Ir2O7

We investigated the magnetoresistance (MR) effect of the pyrochlore oxide Nd2Ir2O7, which shows a metal-insulator transition at T-MI = 33 K. A small positive MR effect was observed in the metallic state above TMI, while a large negative MR effect was observed in the insulating state below TMI. MR effects ([rho(B = 0) - rho(B)]/rho(B)) exceeding 3000% were found at 1K at a field of 9 T. As a result, we confirmed the crossover from the insulating state to a state with a small or partial band gap in a field up to 56 T. Furthermore, from the MR effect in Eu2Ir2O7 (T-MI = 120 K) and Gd2Ir2O7 (T-MI = 127 K), we revealed that the large negative MR effect of the pyrochlore iridate Ln(2)Ir(2)O(7) depends on the magnetism of the lanthanide Ln(3+) ion. The d-f interaction plays a significant role in the large negative MR effect in the insulating state.