We establish the double perovskite Ba2CeIrO6 as a nearly ideal model system for j=1/2 moments, with resonant inelastic x-ray scattering indicating a deviation of less than 1% from the ideally cubic j=1/2 state. The local j=1/2 moments form an fcc lattice and are found to order antiferromagnetically at TN=14K, more than an order of magnitude below the Curie-Weiss temperature. Model calculations show that the geometric frustration of the fcc Heisenberg antiferromagnet is further enhanced by a next-nearest neighbor exchange, indicated by ab initio theory. Magnetic order is driven by a bond-directional Kitaev exchange and by local distortions via a strong magneto-elastic effect - both effects are typically not expected for j=1/2 compounds making Ba2CeIrO6 a riveting example for the rich physics of spin-orbit entangled Mott insulators.
@article{arxiv.1901.06215,
title = {Spin-orbit entangled j=1/2 moments in Ba$_2$CeIrO$_6$ -- a frustrated fcc quantum magnet},
author = {A. Revelli and C. C. Loo and D. Kiese and P. Becker and T. Fröhlich and T. Lorenz and M. Moretti Sala and G. Monaco and F. L. Buessen and J. Attig and M. Hermanns and S. V. Streltsov and D. I. Khomskii and J. van den Brink and M. Braden and P. H. M. van Loosdrecht and S. Trebst and A. Paramekanti and M. Grüninger},
journal= {arXiv preprint arXiv:1901.06215},
year = {2019}
}