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Cubic symmetry and magnetic frustration on the fcc spin lattice in K2IrCl6Khan, N.; Prishchenko, D.; Scurschii, I.; Mazurenko, V. G.; Tsurlin, A. A.
Cubic crystal structure and regular octahedral environment of Ir4+ render antifluorite-type K2IrCl6 a model fcc antiferromagnet with a combination of Heisenberg and Kitaev exchange interactions. High-resolution synchrotron powder diffraction confirms cubic symmetry down to at least 20 K, with a low-energy rotary mode gradually suppressed upon cooling. Using thermodynamic and transport measurements, we estimate the activation energy of Δ ≃ 0.7 eV for charge transport, the antiferromagnetic Curie-Weiss temperature of θCW ≃ −43 K, and the extrapolated saturation field of Hs ≃ 87 T. All these parameters are well reproduced ab initio using Ueff = 2.2 eV as the effective Coulomb repulsion parameter. The antiferromagnetic Kitaev exchange term of K ≃ 5 K is about one half of the Heisenberg term J ≃ 13 K. While this combination removes a large part of the classical ground-state degeneracy, the selection of the unique magnetic ground state additionally requires a weak second-neighbor exchange coupling J2 ≃ 0.2 K. Our results suggest that K2IrCl6 may offer the best possible cubic conditions for Ir4+ and demonstrates the interplay of geometrical and exchange frustration in a high-symmetry setting.
Physical Review B 99(2019), 144425
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