Structural, electronic, and magnetic properties of nearly ideal <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:msub><mml:mi>J</mml:mi><mml:mrow><mml:mi>e</mml:mi><mml:mi>f</mml:mi><mml:mi>f</mml:mi></mml:mrow></mml:msub><mml:mo>=</mml:mo><mml:mfrac><mml:mn>1</mml:mn><mml:mn>2</mml:mn></mml:mfrac></mml:mrow></mml:math> iridium halides

Abstract

Heavy transition metal magnets with ${J}_{eff}=\frac{1}{2}$ 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 ${J}_{eff}=\frac{1}{2}$ states are scarce due to the importance of noncubic local distortions in most candidate materials. In this work, we identify a family of iridium halide systems [i.e., ${\mathrm{K}}_{2}\mathrm{Ir}{\mathrm{Cl}}_{6}$, ${\mathrm{K}}_{2}\mathrm{Ir}{\mathrm{Br}}_{6}$, ${({\mathrm{NH}}_{4})}_{2}\mathrm{Ir}{\mathrm{Cl}}_{6}$, and ${\mathrm{Na}}_{2}\mathrm{Ir}{\mathrm{Cl}}_{6}\ifmmode\cdot\else\textperiodcentered\fi{}6({\mathrm{H}}_{2}\mathrm{O})]$ with ${\mathrm{Ir}}^{4+}$ electronic ground states exhibiting extremely small deviations from the ideal ${J}_{eff}=\frac{1}{2}$ limit. We also find ordered magnetic ground states for the three anhydrous systems, with single-crystal neutron diffraction on ${\mathrm{K}}_{2}\mathrm{Ir}{\mathrm{Br}}_{6}$ revealing type-I antiferromagnetism. This spin configuration is consistent with expectations for significant Kitaev exchange in a face-centered-cubic magnet. This work establishes that incorporating isolated $\mathrm{Ir}{X}_{6}$ octahedra in materials, where $X$ is a halogen ion with a low electronegativity, is an effective design principle for realizing unprecedented proximity to the pure ${J}_{eff}=\frac{1}{2}$ state. At the same time, we highlight undeniable deviations from this ideal state, even in clean materials with ideal $\mathrm{Ir}{X}_{6}$ octahedra as inferred from the global cubic crystal structures.

Topics & Concepts