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 Fm3¯m, 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.