T. Kraft

Calculated magneto-optical Kerr spectra of compounds (X = V, Cr, Mn, Fe and Co)

The magneto-optical spectra of the compounds (with X = V, Cr, Mn, Fe and Co) are calculated for their ferromagnetic phase in the crystal structure, using density-functional band-structure theory. Large polar Kerr effects are predicted for several of these compounds, with - for a reasonable spectral broadening of 0.4 eV - maximum Kerr rotations of for and , for and , respectively. The Kerr spectra of , and with (001) magnetization are found to be very similar in shape, as are also those of and . The origin of the large Kerr effect in the alloys is shown to be caused by the spin - orbit coupling strength of Pt. A magnetic moment of moderate size on the 3d atom suffices in these materials to already create an appreciable Kerr effect. The influence of the optical transition matrix elements, magnetic moments and spin - orbit coupling strength on each of the constituent atoms are furthermore analysed. The orientation dependence of the polar Kerr spectra of some of the compounds are investigated by calculating in addition the polar Kerr spectra of some compounds for the (111) magnetization axis. The Kerr spectra of the (111) magnetization are found to be practically identical to that of the (001) magnetization.

First‐principles study of the giant magneto‐optical Kerr effect in MnBi and related compounds

First‐principles band‐structure calculations of the magneto‐optical Kerr spectra of MnBi and related compounds are reported. We find that band‐structure theory, based on density‐functional theory in the local spin‐density approximation, explains the measured Kerr effect of MnBi very well. A giant Kerr rotation of about −1.75° at 1.8 eV photon energy is given by our ab initio calculations, in accordance with recent experiments. A second peak at 3.4 eV in the Kerr rotation spectrum, however, comes out smaller in our calculations than what was recently measured. It is discussed that this can be due to the Mn–Bi stoichiometry. The microscopic origin of the giant Kerr effect in MnBi is analyzed in detail. We find that the huge Kerr effect in MnBi is caused by the combination of a sizeable magnetic moment of 3.7 μB on manganese, the large spin‐orbit coupling of bismuth, and a strong hybridization between the manganese d bands and the bismuth p states. The magneto‐optically active states are mainly the p states ...

Optical and magneto-optical spectroscopy of uranium and plutonium compounds: recent theoretical progress

Abstract First-principles calculations are reported which illustrate that, for those actinide compounds where the 5f electrons are sufficiently delocalized, energy band theory based upon the local spin-density approximation (LSDA) describes the optical and MO spectra reasonably well. Examples which we examine in detail are URhAl and UFe2. The delocalized LSDA approach meets limitations for those actinide compounds, where the electrons in the correlated 5f shell are nearly localized. Just as in the case of lanthanide compounds having localized 4f electrons, a satisfactory description of the optical spectra could be obtained by using a generalization of the LSDA, in which explicitly f electron Coulomb correlations are taken into account (LSDA+U approach). A third group consists of compounds in which the 5f electrons are neither fully delocalized nor localized, but have experimentally been classified as quasilocalized. The suitable theoretical approach to such compounds is yet to be resolved. We further consider the Pu monochalcogenides, the unusual physical properties of which were previously treated with different models, and discuss the optical spectrum of PuTe.

Theory of the optical and magneto-optical spectra of cerium and uranium compounds

Abstract The optical and magneto-optical (MO) spectra of cerium and uranium compounds are investigated theoretically, using an energy-band approach in combination with the linear-response formalism. The energy bands are obtained within the local-density approximation (LDA), as well as with its generalization in which explicit on-site Coulomb correlations are included (LDA+U). We find that for CeSb, CeSe, and CeTe the LDA+U approach gives an adequate description of the measured MO spectra. For CeSb we calculate a colossal MO Kerr rotation of about 60°, which is in agreement with recent experiments. For the uranium compounds we find that the LDA gives a good description of the MO spectra, if the 5f-electrons are sufficiently delocalized, as is illustrated by e.g., UAsSe. The MO spectra of the uranium monochalcogenides US, USe, and UTe pose a challenge to present-day correlated band theory: it is shown that for UTe, where the 5f-electrons are quasilocalized, the LDA+U approach gives a reasonable result. For US, and also for USe, a better description is obtained if, as a correction beyond the on-site Coulomb interaction U, a screened hole in the 5f-shell is taken into account.

Theory of the anisotropic magneto-optical Kerr effect in (1120) and (0001) hcp Co and in (110) and (100) fcc Co

The magneto-optical polar Kerr effect in hcp and fcc Co is studied theoretically for two magnetization orientations, the (1120) and (0001) orientation for hcp Co, and the (110) and (100) orientation for fcc Co. The theoretical Kerr spectra of (110) and (100) fcc Co display a negligibly small magnetocrystalline anisotropy. The Kerr spectra of the (1120) and (0001) orientation of hcp Co show a distinct anisotropy, which is in agreement with recent measurements. It is concluded that band structure theory, using density-functional theory in the local-density approximation (LDA) can qualitatively describe the magnetocrystalline anisotropy in the Kerr spectra of Co.