Resonant x-ray magnetic scattering from CoO

We analyze the recent experiment [W. Neubeck et al.: Phys. Rev. B 60 (1999) R9912] for the resonant x-ray magnetic scattering (RXMS) around the K edge of Co in the antiferromagnet CoO. We propose a mechanism of the RXMS that makes the 4p states couple to the magnetic order: the intraatomic exchange interaction between the 4p and the 3d states and the p-d mixing to the 3d states of neighboring Co atoms. These couplings induce the orbital moment in the 4p states and make the scattering tensor antisymmetric. Using a cluster model, we demonstrate that this modification gives rise to a large RXMS intensity in the dipole process, in good agreement with the experiment. We also find that the pre-edge peak is generated by the transition to the 3d states in the quadrupole process, with negligible contribution of the dipole process. We also discuss the azimuthal angle dependence of the intensity.