Metal-Insulator Transition and Magnetic Order in the Pyrochlore Oxide Hg2Ru2O7

TL;DR

This study investigates the metal-insulator transition and magnetic ordering in Hg2Ru2O7, revealing a transition at 107 K with antiferromagnetic order and small magnetic moments, challenging localized spin models.

Contribution

The paper provides experimental evidence of antiferromagnetic order and small magnetic moments in Hg2Ru2O7, offering new insights into its electronic and magnetic properties during the transition.

Findings

Metal-insulator transition at 107 K in Hg2Ru2O7.

Observation of antiferromagnetic order with small magnetic moments.

Absence of substantial spin correlations in the metallic phase.

Abstract

We report results of NMR experiments on the ruthenium oxide Hg2Ru2O7 with the pyrochlore structure, which exhibits a metal-insulator transition at TMI = 107 K. In the metallic phase above TMI, the nuclear spin-lattice relaxation rate 1/T1 and the Knight shift at the Hg sites follow the Korringa relation, indicating the absence of substantial spatial spin correlation. At low temperatures in the insulating phase, 99,101Ru-NMR signals are observed at zero magnetic field, providing evidence for a commensurate antiferromagnetic order. The estimated ordered moment is about 1 muB per Ru, much smaller than 3 muB expected for the ionic (4d)3plus configuration of Ru5plus. Thus the localized spin models are not appropriate for the insulating phase of Hg2Ru2O7. We also discuss possible antiferromagnetic spin structures.