Anomalous metallic conductivity and short-range ferromagnetic correlation in high-pressure synthesized pyrochlore

¹ Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences Beijing 100190, China
² National Synchrotron Radiation Research Center (NSRRC) - 101 Hsin-Ann Road, Hsinchu 30076, Taiwan
³ Max-Planck Institute for Chemical Physics of Solids - Nothnitzer Straße 40, Dresden 01187, Germany
⁴ Center for High Pressure Science & Technology Advanced Research - Beijing 100094, China

Received: 21 November 2023
Accepted: 12 February 2024

Abstract

Iridates show fascinating properties due to the unpredictable ground states of their Ir cations. Generally, Ir⁵⁺(5d⁴) systems exhibit insulating nonmagnetic states owing to the strong spin-orbit coupling (SOC). Herein a new pyrochlore iridate Hg₂Ir₂O₇ with an Ir⁵⁺ charge state synthesized by high-pressure technique is reported. Hg₂Ir₂O₇ crystallizes in the typical cubic pyrochlore crystal structure. The Ir⁵⁺ valence state is evidenced by the XAS spectrum. Surprisingly, Hg₂Ir₂O₇ displays short-range ferromagnetic correlations at low temperatures as evidenced by S-shape field-dependent magnetization curves, positive magnetoresistance, and magnetic excitations in specific heat. Furthermore, it also shows metallic conduction and large electron component of specific heat. These results all indicate that Ir⁵⁺ in Hg₂Ir₂O₇ deviates from SOC-dominated insulating nonmagnetic states.