V. N. Antonov

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 1.8u2009eV photon energy is given by our ab initio calculations, in accordance with recent experiments. A second peak at 3.4u2009eV 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 3.7u2009μB 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 ...

The optical properties of

The optical properties of have been deduced using spectrophotometry and ellipsometry and calculated within the extended linear augmented plane wave framework in the energy range 0 - 6 eV. Good agreement amongst all approaches is obtained up to about 2 eV, beyond which there is some divergence between theory and experiment where, for reasons discussed, the theory needs further refinement.

Coulomb-Enhanced Spin-Orbit Splitting: The Missing Piece in the Sr2RhO4 Puzzle

The outstanding discrepancy between the measured and calculated (local-density approximation) Fermi surfaces in the well-characterized, paramagnetic Fermi liquid Sr2RhO4 is resolved by including the spin-orbit coupling and Coulomb repulsion. This results in an effective spin-orbit coupling constant enhanced 2.15 times over the bare value. A simple formalism allows discussion of other systems. For Sr2RhO4, the experimental specific-heat and mass enhancements are found to be 2.2.

Theory of the giant magneto-optical Kerr effect in MnPt3 and PtMnSb

Abstract The magueto-optical (MO) Kerr effect in the manganese-platinum compounds MnPt 3 and PtMnSb is studied from first principles, using density-functional band-structure theory. The calculated Kerr spectra give a good description of the huge Kerr rotations found experimentally in these compounds. The origin of the Kerr rotation is discussed in relationship to the band structure and the spin-orbit (SO) interaction strength of Pt.

Experimental and ab initio theoretical study of optical and magneto-optical properties of Co/Cu multilayers

The polar Kerr rotation and ellipticity spectra were measured in the spectral range 0.8 - 5.5 eV for a set of Co/Cu multilayered structures (MLS). The magneto-optical (MO) response of Co/Cu MLS being related to the -part of the optical conductivity tensor was obtained from the Kerr spectra and tensor component , determined by spectroscopic ellipsometry. The self-consistent spin-polarized fully relativistic linear muffin-tin orbital method within the local spin-density approximation was used to calculate the electronic structure, optical, and MO properties of some model Co/Cu MLS. Good agreement between the measured and calculated optical and MO spectra is observed. The role of the spin - orbit coupling and exchange splitting at the Co and Cu sites, and the hybridization effects are examined and discussed. The spin-polarized Cu interface states appear to give a weak contribution to the - and Kerr spectra whereas the latter ones are strongly influenced by the Cu-dominated optical spectra structure. The results obtained demonstrate that the MO properties of real large-period multilayered structures can be quantitatively predicted from first-principles band-structure calculations.

Fermi surface, bonding, and pseudogap in MoSi2

Abstract The electronic structure and Fermi surface of molybdenum disilicide has been calculated using local-density functional theory (LDA) and the linear muffin-tin orbital method (LMTO). The energy bands are analyzed in detail for their orbital character. Our explanation for the presence of a pseudogap after the seventh band is that the two Si s bands lie low and that there are five Mo d-Si p pair bands. The configuration is approximately Mo 4d5 Si2 3s2 3p2.5. An explanation in terms of directed bond-orbitals was not achieved. The calculated angular dependence of the extremal Fermi surface cross-section areas are in good qualitative agreement with de Haas-van Alphen (dHvA) measurements. However, in order to obtain quantitative agreement, the Mo dx2−y2 orbital energy has to be shifted upwards by 0.41 eV and the Mo dxy energy downwards by 0.20 eV. This deficiency is ascribed to the use of a local exchange-correlation potential.

Spin/orbit moment imbalance in the near-zero moment ferromagnetic semiconductor SmN

SmN is ferromagnetic below 27 K, and its net magnetic moment of 0.03 Bohr magnetons per formula unit is one of the smallest magnetisations found in any ferromagnetic material. The near-zero moment is a result of the nearly equal and opposing spin and orbital moments in the 6H5/2 ground state of the Sm3+ ion, which leads finally to a nearly complete cancellation for an ion in the SmN ferromagnetic state. Here we explore the spin alignment in this compound with X-ray magnetic circular dichroism at the Sm L2,3 edges. The spectral shapes are in qualitative agreement with computed spectra based on an LSDA+U (local spin density approximation with Hubbard-U corrections) band structure, though there remain differences in detail which we associate with the anomalous branching ratio in rare-earth L edges. The sign of the spectra determine that in a magnetic field the Sm 4f spin moment aligns antiparallel to the field; the very small residual moment in ferromagnetic SmN aligns with the 4f orbital moment and antiparallel to the spin moment. Further measurements on very thin (1.5 nm) SmN layers embedded in GdN show the opposite alignment due to a strong Gd-Sm exchange, suggesting that the SmN moment might be further reduced by about 0.5 % Gd substitution.

Electronic Structure of Strongly Correlated Systems

The article reviews the rich phenomena of metal-insulator transitions, anomalous metalicity, taking as examples iron and titanium oxides. The diverse phenomena include strong spin and orbital fluctuations, incoherence of charge dynamics, and phase transitions under control of key parameters such as band filling, bandwidth, and dimensionality. Another important phenomena presented in the article is a valence fluctuation which occur often in rare-earth compounds. We consider some Ce, Sm, Eu, Tm, and Yb compounds such as Ce, Sm and Tm monochalcogenides, Sm and Yb borides, mixed-valent and charge-ordered Sm, Eu and Yb pnictides and chalcogenides R4X3 and R3X4 (R = Sm, Eu, Yb; X = As, Sb, Bi), intermediate-valence YbInCu4 and heavy-fermion compounds YbMCu4 (M = Cu, Ag, Au, Pd). Issues addressed include the nature of the electronic ground states, the metal-insulator transition, the electronic and magnetic structures. The discussion includes key experiments, such as optical and magneto-optical spectroscopic measurements, x-ray photoemission and x-ray absorption, bremsstrahlung isochromat spectroscopy measurements as well as x-ray magnetic circular dichroism.

Magneto-optical spectroscopy of d- and f-ferromagnetic materials: recent theoretical progress (Review Article)

The current status of theoretical understanding of the optical and magneto-optical (MO) spectra of 3d, 4f and 5f compounds is reviewed. Energy band theory based upon the local spin-density approximation (LSDA) describes the optical and MO spectra of transition metal compounds reasonably well. Examples which we examine in detail are XPt3 compounds (with X=3d V, Cr, Mn, Fe, and Co) in the AuCu3 structure, ternary Heusler alloys NiMnSb, PdMnSb, PtMnSb, and MnBi compound. The LSDA, which is capable of describing the spectra of transition-metal alloys with high accuracy, does not suffice for lanthanide compounds having a correlated 4f shell. 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). As examples of this group we consider CeSb and CeBi. For CeSb a record Kerr angle of 90° was very recently reported, 90° is the absolute maximum value that can be measured. I...

Influence of disorder on the magneto-optical properties of FePt

Abstract A scheme to deal with the magneto-optical properties of randomly disordered alloys is presented. This aim is achieved by calculating the optical conductivity tensor α(ω) for a number of ordered model compounds that differ in their atomic configuration within the unit cell but not in their composition. In a subsequent step the orientational and configurational average 〈α(ω)〉 is taken. The magneto-optical properties are derived then from this in the conventional way. As it is demonstrated for FePt this approach accounts for the the influence of disorder on its magneto-optical properties in a very satisfying way.