  In this study, we performed powder neutron diffraction and inelastic
scattering measurements of frustrated pyrochlore Nd$_2$Ir$_2$O$_7$, which
exhibits a metal-insulator transition at a temperature $T_{\rm MI}$ of 33 K.
The diffraction measurements revealed that the pyrochlore has an
antiferromagnetic long-range structure with propagation vector $\vec{q}_{0}$ 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 Nd$^{3+}$ magnetic moments of magnitude $2.3\pm0.4$$\mu_{\rm B}$,
where $\mu_{\rm B}$ is the Bohr magneton. The inelastic scattering measurements
revealed that the Kramers ground doublet of Nd$^{3+}$ splits below $T_{\rm
MI}$. 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.
