Magnetic order and the electronic ground state in the pyrochlore iridate Nd ₂Ir ₂O ₇

We report a muon spin relaxation/rotation, bulk magnetization, neutron scattering, and transport study of the electronic properties of Nd ₂Ir ₂O ₇. We observe the onset of strongly hysteretic behavior in the temperature-dependent magnetization below 120 K, and an abrupt increase in the temperature-dependent resistivity below 8 K. Muon spin relaxation measurements show that the hysteretic magnetization is driven by a transition to a magnetically disordered state, and below 8 K a magnetically ordered ground state sets in, as evidenced by the onset of spontaneous muon precession. Our measurements point toward the absence of a true metal-to-insulator phase transition in this material and suggest that Nd ₂Ir ₂O ₇ may lie within or on the metallic side of the boundary of the Dirac semimetal regime within its topological phase diagram.