Emergence of Magnetic Long-range Order in Frustrated Pyrochlore Nd2Ir2O7 with Metal-Insulator Transition

In this study, we performed powder neutron diffraction and inelastic scattering measurements of frustrated pyrochlore Nd2Ir2O7, which exhibits a metal-insulator transition at a temperature T-MI of 33 K. The diffraction measurements revealed that the pyrochlore has an antiferromagnetic long-range structure with propagation vector q(0) of (0, 0, 0) and that it grows with decreasing temperature below 15 K. This structure was analyzed to be of the all-in all-out type, consisting of highly anisotropic Nd3+ magnetic moments of magnitude 2.3 +/- 0.4 mu(B), where mu(B) is the Bohr magneton. The inelastic scattering measurements revealed that the Kramers ground doublet of Nd3+ splits below T-MI. This suggests the appearance of a static internal magnetic field at the Nd sites, which probably originates from a magnetic order consisting of Ir4+ magnetic moments. Here, we discuss a magnetic structure model for the Ir order and the relation of the order to the metal-insulator transition in terms of frustration.