Relativistic calculations of the magneto-optical Kerr spectra in (001) and (111) US, USe, and UTe

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Abstract
The magneto-optical (MO) Kerr spectra of the isochemical uranium compounds US, USe, and UTe are investigated from first principles, using density-functional theory in the local spin-density approximation and the relativistic augmented-spherical-wave band-structure method. Fully relativistic, optical transition-matrix elements are derived from Dirac theory. The ab initio calculated Kerr spectra compare reasonably well with experimental spectra in height, but the theoretical spectra exhibit a double peak structure, whereas the experimental ones show only one peak and a vague shoulder. To explain this difference, attention is first given to anisotropy effects related to the strong magnetic anisotropy present in these compounds. Polar Kerr spectra are calculated for two magnetization directions, the (001) and (111) (i.e., easy axis) directions. A clear anisotropy is found in the Kerr spectra of these two magnetizations, but the differences between experimental and theoretical spectra cannot be related to the magnetic anisotropy. Secondly, the influences of the lattice spacing and of an external magnetic field on the Kerr spectra are investigated, but no explanation of the differences found can be derived thereof. The band structures and Kerr spectra obtained by the ASW method are furthermore checked by recalculating them with a fully relativistic linear muffin-tin orbital scheme and are found to be essentially the same. The positions of the ab initio energy bands are in addition in accordance with experimentally determined band positions. The origin of the difference in the Kerr spectra is discussed in relationship to electron-correlation effects and to the orbital polarization.