The magnetic structure of honeycomb iridate Na2IrO3 is of paramount importance to its exotic properties. The magnetic order is established experimentally to be zigzag antiferromagnetic. However, the previous assignment of ordered moment to the a-axis is tentative. We examine the magnetic structure of Na2IrO3 using first-principles methods. Our calculations reveal that total energy is minimized when the zigzag antiferromagnetic order is magnetized along g≈a+c. Such a magnetic configuration is explained by adding anisotropic interactions to the nearest-neighbor Kitaev-Heisenberg model. Spin-wave spectrum is also calculated, where the calculated spin gap of 10.4 meV can in principle be measured by future inelastic neutron scattering experiments. Finally we emphasize that our proposal is consistent with all known experimental evidence, including the most relevant resonant x-ray magnetic scattering measurements [X. Liu \emph{et al.} {Phys. Rev. B} \textbf{83}, 220403(R) (2011)].
@article{arxiv.1504.02699,
title = {Computational Study of the Magnetic Structure of Na$_2$IrO$_3$},
author = {Kaige Hu and Fa Wang and Ji Feng},
journal= {arXiv preprint arXiv:1504.02699},
year = {2015}
}