Magnetic dichroism in uv photoemission from valence bands: Geometries where the three-step model of photoemission predicts null results

Magnetic dichroism in the angular distribution of photoelectrons (MDAD) with ultraviolet light has been used to investigate the valence bands of thin Co films on Cu(001), employing an experimental geometry with off-normal electron emission in a mirror plane which is perpendicular to the in-plane magnetization. The magnetic dichroism is particularly surface sensitive in this geometry, so that both an atomic model and the three-step model of photoemission predict zero magnetic dichroism. Despite this, features in the dichroism spectra disperse with k_⊥ (the electron wave vector perpendicular to the surface), showing that the MDAD contains magnetic information concerning the bulk band structure. Instances of bulk band crossing and hybridization by spin-orbit coupling are readily identified, and the dispersion of unhybridized bands can be resolved within the broad intensity peaks of conventional photoemission. These results illustrate that the utility of MDAD as a rapid survey technique for study of the valence bands of $3d$ ferromagnets is not restricted to high symmetry directions.