Magnetic circular dichroism inL3M2,3M2,3Auger emission from Fe and Co metals due to symmetry-breaking interactions

Abstract

A strong magnetic circular dichroism (MCD) in the ${L}_{3}{M}_{2,3}{M}_{2,3}$ Auger-electron emission spectra was measured on Fe and Co metal in the off-resonance energy region with the light helicity vector perpendicular to the magnetization direction, despite the fact that this emission is expected to be symmetry forbidden in this geometry. The experimental results are explained quantitatively by taking into account the exchange interaction of the spin-orbit split core states with the spin-polarized valence band. It is shown that the local valence-band magnetic moment is strongly suppressed in the presence of a $2p$ hole in the intermediate state. As a result the MCD signal decreases going from Fe to Co metal, while for Ni the MCD is no longer observable. This behavior is completely different for the measurements at resonance---i.e., at the ${L}_{3}$ absorption edge, where the MCD signal is strong $(\ensuremath{\sim}9%)$ for Fe, Co, and Ni due to the large spin polarization of the $2p$ core hole which is caused by unoccupied $3d$ states with predominantly minority spin in the vicinity of the Fermi level.