Direct determination of the spin structure of Nd${}_2$Ir${}_2$O${}_7$ by means of neutron diffraction

Abstract

We report on the spin structure of the pyrochlore iridate Nd${}_2$Ir${}_2$O${}_7$ 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) $\hat{I}{¼}_{\mathrm{B}}$/Ir${}^{4+}$ and 1.27(1) $\hat{I}{¼}_{\mathrm{B}}$/Nd${}^{3+}$. The Nd${}^{3+}$ moment size at 1.8 K is smaller than that expected for the Nd${}^{3+}$ ground state doublet. On the other hand, the size of the ordered moments of the Ir${}^{4+}$ ions at 1.8 K agrees very well with the value expected for a $J_{\mathrm{eff}}$ = 1/2 state based on the presence of strong spin-orbit coupling in this system. Finally, our measurements reveal a parallel alignment of the Nd${}^{3+}$ moments with the net moment of its six nearest neighboring Ir${}^{4+}$ ions.

http://journals.aps.org/prb/pdf/10.1103/PhysRevB.94.161102