  We study the resonant x-ray magnetic scattering (RXMS) around the K edge of
Ni in the antiferromagnet NiO, by treating the 4p states of Ni as a band and
the 3d states as localized states. We propose a mechanism that the 4p states
are coupled to the magnetic order through the intra-atomic Coulomb interaction
between the 4p and the 3d states and through the p-d mixing to the 3d states of
neighboring Ni atoms. These couplings induce the orbital moment in the 4p band,
and thereby give rise to the RXMS intensity at the K edge in the dipolar
process. It is found that the spin-orbit interaction in the 4p band has
negligibly small contribution to the RXMS intensity. The present model
reproduces well the experimental spectra. We also discuss the azimuthal angle
dependence of the intensity.
