Emergence of magnetic long-range order in frustrated pyrochlore Nd$_2$Ir$_2$O$_7$ with metal-insulator transition

TL;DR

This study reveals the emergence of antiferromagnetic long-range order in Nd$_2$Ir$_2$O$_7$ below 15 K, linked to a metal-insulator transition at 33 K, involving Nd and Ir magnetic moments and frustration effects.

Contribution

It provides the first detailed neutron diffraction and inelastic scattering analysis of magnetic order and Nd$^{3+}$ splitting in Nd$_2$Ir$_2$O$_7$, connecting magnetic structure to the metal-insulator transition.

Findings

Antiferromagnetic all-in all-out structure with propagation vector (0,0,0)

Magnetic order develops below 15 K

Nd$^{3+}$ Kramers doublet splits below T_MI

Abstract

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.