Magnetic order in the pyrochlore iridate Nd2Ir2O7probed by muon spin relaxation

Abstract

Muon spin relaxation results on the pyrochlore iridate Nd${}_{2}$Ir${}_{2}$O${}_{7}$ are reported. Spontaneous coherent muon spin precession below the metal-insulator transition (MIT) temperature of about 33 K is observed, indicating the appearance of a long-range magnetic ordering of Ir${}^{4+}$ moments. With further decrease in temperature, the internal field at the muon site increases again below about 9 K. The second increase of internal field suggests the ordering of Nd${}^{3+}$ moments, which is consistent with a previous neutron experiment. Our results suggest that the MIT and magnetic ordering of Ir${}^{4+}$ moments have a close relationship and that the large spin-orbit coupling of Ir 5$d$ electrons plays a key role for both MIT and the mechanism of the magnetic ordering in pyrochlore iridates in the insulting ground state.