K-edge resonant x-ray magnetic scattering from CoO

We report the observation of two contributions to resonant x-ray magnetic scattering experiments performed at the K edge of Co in the antiferromagnet CoO. By using polarization analysis of the scattered x-ray beam, the two resonances have been clearly associated to a quadrupolar resonance $\left(1\mathrm{}\overrightarrow{s}3d\right)$ and a dipolar resonance $\left(1\mathrm{}\overrightarrow{s}4p\right),$ respectively. The quadrupolar resonance is related to the magnetization of the $3d$ bands and to the existence of a net orbital moment, whereas the dipolar resonance must be related to spin-orbit splitting of the (empty) Co $4p$ states.