Emergence of Magnetic Long-range Order in Frustrated Pyrochlore Nd2Ir2O7with 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 TMI of 33 K. The diffraction measurements revealed that the pyrochlore has an antiferromagnetic long-range structure with propagation vector q⃗₀ 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±0.4μB$, where $μB$ is the Bohr magneton. The inelastic scattering measurements revealed that the Kramers ground doublet of Nd$³⁺$ splits below $TMI$. This suggests the appearance of a static internal magnetic field at the Nd sites, which probably originates from a magnetic order consisting of Ir$⁴⁺$ 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.