Evolution of Magnetic Excitations Across the Metal-Insulator Transition in a Pyrochlore Iridate Eu$_{2}$Ir$_{2}$O$_{7}$

TL;DR

This study uses RIXS to investigate magnetic excitations in Eu₂Ir₂O₇, revealing how magnon modes soften and dampen across the metal-insulator transition, highlighting the importance of electron itinerancy in its magnetic behavior.

Contribution

First RIXS investigation of magnetic excitations in Eu₂Ir₂O₇ across its metal-insulator transition, showing the significance of electron itinerancy in its magnetic properties.

Findings

Magnon mode with 20 meV bandwidth and 28 meV gap at 7 K

Substantial magnon softening near transition temperature

Magnetic excitations become highly damped in the paramagnetic phase

Abstract

We report Resonant Inelastic X-ray Scattering (RIXS) study of the magnetic excitation spectrum in a highly insulating Eu$_{2}$Ir$_{2}$O$_{7}$ single crystal that exhibits a metal-insulator transition at $T_{MI}$ = 111(7) K. A propagating magnon mode with 20 meV bandwidth and 28 meV magnon gap is found in the excitation spectrum at 7 K, which is expected in the all-in-all-out (AIAO) magnetically ordered state. This magnetic excitation exhibits substantial softening as temperature is raised towards $T_{MI}$, and turns into highly damped excitation in the paramagnetic phase. Remarkably, the softening occurs throughout the whole Brillouin zone including the zone boundary. This observation is inconsistent with magnon renormalization expected in a local moment system, and indicates that the strength of electron correlation in Eu$_{2}$Ir$_{2}$O$_{7}$ is only moderate, so that electron itinerancy should be taken into account in describing its magnetism.