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 Kα and Mg Kα 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. copyright 1998 The American Physical Society