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

TL;DR

This study explores the giant magnetoresistance effects in Nd2Ir2O7 and related pyrochlore iridates, revealing a crossover from metallic to insulating states and the influence of lanthanide magnetism on MR behavior.

Contribution

It demonstrates the large negative magnetoresistance in pyrochlore iridates and highlights the role of d-f interactions and lanthanide magnetism in this phenomenon.

Findings

MR exceeds 3000% at 1 K and 9 T

Crossover from insulating to partial band gap state in high magnetic fields

Large negative MR depends on lanthanide ion magnetism

Abstract

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 T_MI, while a large negative MR effect was observed in the insulating state below T_MI . MR effects exceeding 3000% were found at 1 K 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 Gd$_2$Ir$_2$O$_7$ (T_MI = 127 K), we revealed that the large negative MR effect of the pyrochlore iridate Ln2Ir2O7 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.