Orbital moment and magnetic circular dichroism at the K edge in ferromagnetic cobalt

We study the orbital moment and the magnetic circular dichroism (MCD) at the K edge for ferromagnetic Co on the basis of a tight-binding model including the spin-orbit interaction. We find that the MCD spectra have negative values near the photothreshold up to similar to 7 eV in agreement with the experiment. The spin-orbit interaction of the 3d states plays a dominant role in generating the MCD spectra, similar to the previous study for Ni and Fe. We show that a positive peak grows at the vicinity of the photothreshold in the MCD spectra with decreasing values of the occupied electron number from that for Co within the fee structure. When the atomic value is used for the spin-orbit coupling coefficient, the intensity of the MCD spectra and the orbital moment are nearly half the experimental values. We remove this discrepancy by taking account of the enhancement effect due to the intra-atomic Coulomb interaction.