Direct determination of the spin structure of Nd₂Ir₂O₇ by means of neutron diffraction

We report on the spin structure of the pyrochlore iridate Nd2Ir2O7 that could be directly determined by means of powder neutron diffraction. Our magnetic structure refinement unravels a so-called all-in/all-out magnetic structure that appears in both the Nd and the Ir sublattice. The ordered magnetic moments at 1.8 K amount to 0.34(1) mu(B)/Ir4+ and 1.27(1) mu(B)/Nd3+. The Nd3+ moment size at 1.8 K is smaller than that expected for the Nd3+ ground state doublet. On the other hand, the size of the ordered moments of the Ir4+ ions at 1.8 K agrees very well with the value expected for a J(eff) = 1/2 state based on the presence of strong spin-orbit coupling in this system. Finally, our measurements reveal a parallel alignment of the Nd3+ moments with the net moment of its six nearest neighboring Ir4+ ions