Toward cubic symmetry for Ir${}^{4+}$: structure and magnetism of antifluorite K${}_2$IrBr${}_6$

Abstract

Crystal structure, electronic state of Ir${}^{4+}$, and magnetic properties of the antifluorite compound K${}_2$IrBr${}_6$ are studied using high-resolution synchrotron x-ray diffraction, resonant inelastic x-ray scattering (RIXS), thermodynamic and transport measurements, and ab initio calculations. The crystal symmetry is reduced from cubic at room temperature to tetragonal below 170 K and eventually to monoclinic below 122 K. These changes are tracked by the evolution of the non-cubic crystal-field splitting $\Delta$ measured by RIXS. Non-monotonic changes in $\Delta$ are ascribed to the competing effects of the tilt, rotation, and deformation of the IrBr${}_6$ octahedra as well as tetragonal strain on the electronic levels of Ir${}^{4+}$. The Néel temperature of $T_N=11.9$ K exceeds that of the isostructural K${}_2$IrCl${}_6$, and the magnitude of frustration on the fcc spin lattice decreases. We argue that the replacement of Cl by Br weakens electronic correlations and enhances magnetic couplings.

published version: 13 pages + Supplemental Material

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Cited by in corpus (11)

• Quasimolecular electronic structure of the spin-liquid candidate Ba${}_3$InIr${}_2$O${}_9$
• Antiferromagnetic resonance in the cubic iridium hexahalides (NH${}_4$)${}_2$IrCl${}_6$ and K${}_2$IrCl${}_6$
• RIXS interferometry and the role of disorder in the quantum magnet Ba${}_3$Ti${}_{3-x}$Ir${}_x$O${}_9$
• Interplay of magnetic order and ferroelasticity in the spin-orbit coupled antiferromagnet K${}_2$ReCl${}_6$
• Electronic excitations in $5d^4$ J=0 Os${}^{4+}$ halides studied by RIXS and optical spectroscopy
• Vibronic effect on resonant inelastic x-ray scattering in cubic iridium hexahalides
• Local symmetry breaking and low-energy continuum in K${}_2$ReCl${}_6$
• Spin-orbital-lattice entanglement in the ideal j=1/2 compound K${}_2$IrCl${}_6$
• Dynamic Jahn-Teller Phenomena in Heavy Transition Metal Compounds
• Rotational phase transitions in antifluorite-type osmate and iridate compounds
• Sweet spot in the RuCl${}_3$ magnetic system: nearly ideal $j_{\mathrm{eff}}=1/2$ moments and maximized $K/J$ ratio under pressure