1ST PRINCIPLES INVESTIGATIONS OF MCD SPECTRA AND SUM-RULES FOR 3D TRANSITION-METAL SURFACES

Results of precise calculations of the X-ray magnetic-circular-dichroi sm (MCD) spectra and orbital magnetic moment, [L(z)], based on our thi n film full potential linearized augmented plane wave energy band meth od and a tight binding analysis carried out for Fe(001), Co(0001) and Ni(001) surfaces are shown to provide clear physical insight for this new and exciting phenomenon. In addition to the spin magnetic moment e nhancement, the orbital magnetic moment is also found to be enhanced a t the surface due to band narrowing. A double peak structure of the MC D spectra for Fe(001) and Co(0001) is predicted. For Ni(001), the abso rption side peak 6 eV above the main peak is attributed to contributio ns from the d component in a high-lying state. The MCD orbital sum rul e is found to be valid to within 5-10% even in the band approach. Howe ver, for the spin sum rule, large errors are found for Ni systems and, in addition, the magnetic dipole term is also found to be very import ant in this sum rule for atoms without cubic symmetry. This raises a q uestion about the applicability of the spin sum rule to obtain the spi n magnetic moment from MCD spectra. Finally, the effects of a photo-in duced core hole are found to be strongly screened, and to induce an en hancement of [L(z)].