Photoelectron diffraction: A source for magnetic dichroism in angle-resolved photoemission from ferromagnets

Magnetic dichroism has been measured in angle-resolved core-level photoemission from the Fe 2p and 3p levels in epitaxially grown ultrathin films of Fe(001) and in an amorphous metallic glass with composition Fe78B13Si9. Unpolarized Al K alpha and Mg K alpha radiation was used for excitation, leading to diffraction patterns that are dominated by forward scattering along low-index crystallographic directions. The Fe(001) data for both total intensity and magnetic dichroism are quantitatively compared to theoretical calculations at both a two-atom single-scattering level and a multiatom multiple-scattering level. Strong effects on the magnetic dichroism due to photoelectron diffraction are found, and the combined angle and energy dependence of the dichroism shows a characteristic "checkered" pattern that should be generally observable in all single crystals. Comparing dichroism data obtained for single-crystal Fe films with those obtained from the amorphous glass and from two-atom and multiatom diffraction theory further permits estimating the relative contributions of free-atom-like dichroism and of photoelectron diffraction, with the free-atom dichroism (that is dominant 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 dichroism thus should provide a useful tool for studying magnetic order near single-crystal surfaces. The deviation of the zero in the dichroic asymmetry from the low-index directions is also found via photoelectron diffraction theory to be very sensitive to the s-to-d partial-wave phase difference, and the experimental data permit estimating this quantity and the solid-state effects on it.