Magnetic ground state of the pyrochlore iridate Nd₂Ir₂O₇

Pyrochlore iridates are of interest due to the interplay between the relatively large spin-orbit coupling and electron-electron correlations which may induce novel phases such as Weyl semimetals. One important task for understanding the properties of these compounds is the determination of the magnetic structure which is challenging due to the small size of Ir⁴⁺ moments and maybe also due to the neutron absorption from Ir atoms. Our μSR studies on Nd₂Ir₂O₇ clearly show two transitions below about 30 and 9 K related to the Ir and Nd sublattices, respectively. The full magnetic structure including the Ir sublattice has been determined by means of powder neutron diffraction at the high flux D20 diffractometer at the ILL. Our magnetic structure refinement unravels a so-called all-in/all-out magnetic structure for both the Nd and the Ir sublattices. The ordered magnetic moments at 1.8 K amount to 0.34(1) μ_B/Ir⁴⁺ and 1.27(1) μ_B/Nd³⁺.