PHOTOELECTRON DIFFRACTION - A SOURCE FOR MAGNETIC DICHROISM IN ANGLE-RESOLVED PHOTOEMISSION FROM FERROMAGNETS

Magnetic dichroism has been measured in angle-resolved core-level phot oemission from the Fe 2p and 3p levels in epitaxially grown ultrathin films of Fe(001) and in an amorphous metallic glass with composition F e78B13Si9. Unpolarized Al K alpha and Mg K alpha radiation was used fo r excitation, leading to diffraction patterns that are dominated by fo rward scattering along low-index crystallographic directions. The Fe(0 01) data for both total intensity and magnetic dichroism are quantitat ively compared to theoretical calculations at both a two-atom single-s cattering level and a multiatom multiple-scattering level. Strong effe cts on the magnetic dichroism due to photoelectron diffraction are fou nd, and the combined angle and energy dependence of the dichroism show s a characteristic ''checkered'' pattern that should be generally obse rvable in all single crystals. Comparing dichroism data obtained for s ingle-crystal Fe films with those obtained from the amorphous glass an d from two-atom and multiatom diffraction theory further permits estim ating the relative contributions of free-atom-like dichroism and of ph otoelectron diffraction, with the free-atom dichroism (that is dominan t along low-index directions) being smaller by about a factor of 2 to 4 than the maximum diffraction dichroism (that dominates away from low -index directions). Such photoelectron-diffraction-produced magnetic d ichroism thus should provide a useful tool for studying magnetic order near single-crystal surfaces. The deviation of the zero in the dichro ic asymmetry from the low-index directions is also found via photoelec tron diffraction theory to be very sensitive to the s-to-d partial-wav e phase difference, and the experimental data permit estimating this q uantity and the solid-state effects on it.