Structural, electronic, and magnetic properties of nearly-ideal $J_{\rm eff}$ $=$ 1/2 iridium halides

TL;DR

This study identifies iridium halide compounds with nearly ideal $J_{eff}=1/2$ states, despite structural differences, and reveals their magnetic properties, including Type-I antiferromagnetism, relevant for quantum spin liquids and superconductors.

Contribution

The paper reports the discovery of iridium halide systems with near-ideal $J_{eff}=1/2$ states and characterizes their magnetic ground states, expanding the understanding of candidate materials for quantum phenomena.

Findings

Iridium halide compounds exhibit near-ideal $J_{eff}=1/2$ states.

Ordered magnetic ground states observed in these compounds.

Type-I antiferromagnetism confirmed in K$_2$IrBr$_6$.

Abstract

Heavy transition metal magnets with $J_{\rm eff}$ $=$ 1/2 electronic ground states have attracted recent interest due to their penchant for hosting new classes of quantum spin liquids and superconductors. Unfortunately, model systems with ideal $J_{\rm eff}$ $=$ 1/2 states are scarce due to the importance of non-cubic local distortions in most candidate materials. In this work, we identify a family of iridium halide systems [i.e. K$_2$IrCl$_6$, K$_2$IrBr$_6$, (NH$_4$)$_2$IrCl$_6$, and Na$_2$IrCl$_6 \cdotp $ 6(H$_2$O)] with Ir$^{4+}$ electronic ground states in extremely close proximity to the ideal $J_{\rm eff}$ $=$ 1/2 limit, despite a variation in the low-temperature global crystal structures. We also find ordered magnetic ground states for the three anhydrous systems, with single crystal neutron diffraction on K$_2$IrBr$_6$ revealing Type-I antiferromagnetism. This spin configuration is consistent with expectations for significant Kitaev exchange in a face-centered-cubic magnet.