  We explore the phase diagram of spin-orbit Mott insulators on a honeycomb
lattice, within the Kitaev-Heisenberg model extended to its full parameter
space. Zigzag-type magnetic order is found to occupy a large part of the phase
diagram of the model, and its physical origin is explained as due to
interorbital t2g-eg hopping. Magnetic susceptibility and spin wave spectra are
calculated and compared to the experimental data, obtaining thereby the spin
coupling constants in Na2IrO3 and Li2IrO3.
