Mulliken Population Analysis of X-ray Magnetic Circular Dichroism in Uranium Monochalcogenides: Examination of Sum Rules by Fully Relativistic Full-Potential LCAO Method

We study the X-ray magnetic circular dichroism (XMCD) spectra at the U M4,5 and N4,5 edges of uranium monochalcogenides, UX where X=S, Se, and Te, examining the applicability of the XMCD sum rules to UX by the fully relativistic full-potential linear-combination-of-atomic-orbitals (LCAO) method based on the density functional theory. To extract the transitions relevant to the sum-rule analysis, we employ the Mulliken population analysis (MPA). Using the MPA, the orbital sum rule is found to be valid to 10–20% for the M4,5 edges and valid to 5–15% for the N4,5 edges. On the other hand, the spin sum rule is found to be valid to 10–20% for the M4,5 edges whereas valid to 30–35% for the N4,5 edges. Furthermore, it is found that the calculated XMCD spectra are consistent with a recent experimental observation that the intensity of the N4,5 XMCD signal is comparable to that of the M4,5 XMCD signal although contradicting a previous theoretical prediction that the XMCD intensity at the N4,5 edges is one order of magnitude smaller than that at the M4,5 edges