Revisiting the Kitaev material candidacy of Ir4+ double perovskite iridates

Quantum magnets with significant bond-directional Ising interactions, so-called Kitaev materials, have attracted tremendous attention recently in the search for exotic spin liquid states. Here we present a comprehensive set of measurements that enables us to investigate the crystal structures, Ir4+ single-ion properties, and magnetic ground states of the double perovskite iridates La2BIrO6 (B=Mg,Zn) and A2CeIrO6 (A=Ba,Sr) with a large nearest-neighbor distance >5 Å between Ir4+ ions. Our neutron powder diffraction data on Ba2CeIrO6 can be refined in the cubic space group Fm3m, while the other three systems are characterized by weak monoclinic structural distortions. Despite the variance in the noncubic crystal field experienced by the Ir4+ ions in these materials, x-ray absorption spectroscopy and resonant inelastic x-ray scattering are consistent with Jeff=1/2 moments in all cases. Furthermore, neutron scattering and resonant magnetic x-ray scattering show that these systems host A-type antiferromagnetic order. These electronic and magnetic ground states are consistent with expectations for face-centered-cubic magnets with significant antiferromagnetic Kitaev exchange, which indicates that spacing magnetic ions far apart may be a promising design principle for uncovering additional Kitaev materials.