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We calculated the total energy of ferromagnetic (FM) and antiferromagnetic (AFM) GaN:Mn, GaAs:Mn, Ge:Mn and Si:Mn with various distribution of Mn atoms. It is found that the formation of Mn–N–Mn–N chain-like fragments largely lowers the total energy of GaN:Mn. Exchange interaction in the chains has AFM character, so this mechanism can result in a significant decrease of the Curie temperature of GaN:Mn. Our optical calculations show that the formation of such chain-like fragments introduces features in intragap absorption and can be observed in optical measurements. In GaAs:Mn, Ge:Mn and Si:Mn this mechanism is not efficient and the formation of the chains of Mn atoms has no significant effect on Curie temperature.

Optical and magneto-optical data from the perovskite itinerant ferromagnet ${\mathrm{SrRuO}}_{3}$ are presented and compared to fully relativistic, local spin-density approximation band-structure calculations. We find that the basic features of the optical data are well described by the ferromagnetic band calculation. To test recent predictions that the ferromagnetic transition in ${\mathrm{}\mathrm{SrRuO}}_{3}$ is driven by long-wavelength longitudinal spin fluctuations, we track the temperature dependence of the $\mathrm{O}(2p)\ensuremath{\rightarrow}\mathrm{Ru}(4d)$ interband transition which we observe in the magneto-optic conductivity. The absence of significant changes in the energy of this transition suggests that the ferromagnetic order is destroyed largely through transverse, not longitudinal, fluctuations of the ferromagnetic moment. We discuss the implications of these observations for the electronic structure of the ruthenium perovskites.

The electronic structure and optical properties of have been studied by the ab initio full-potential and full-relativistic LMTO methods. Calculations are employed to elucidate the influence of the stacking sequence on the band states and optical spectra. Unusually strong hybridization of the Ca spd states with the Si p states is evident in both of the crystal polymorphs. The Fermi velocities and charge-density distributions indicate significant spatial anisotropy in the TR3 structure. For both of the crystal structures, large in-plane and out-of-plane anisotropy of the optical conductivity has also been found.

The influence of a high magnetic field on the band structure and optical conductivity of FeSi has been studied by the ab initio full-potential LMTO-PW and relativistic LMTO-ASA methods with an applied field included. It is found that the applied external magnetic field induces a metallic magnetic state through a first-order metamagnetic transition, i.e. at a critical magnetic field of about there is a large steplike increase in the calculated magnetization, with a magnetic moment of . The magnetized state persists while the field is gradually reduced from above the metamagnetic transition (a hysteresis effect). The calculated optical conductivity (OC) at the critical field differs substantially from the zero-field OC in the infrared region.

Electronic structure and magnetic properties of Ga 1− x Mn x As, Ga 1− x Mn x N, Zn 1− x M x O, and Zn 1− x M x Te (M=V, Cr, Mn, Fe, and Co) diluted magnetic semiconductors (DMS) are calculated by the tight-binding LMTO method in the 64 atom supercell. Calculations are made at several x with varied spatial distribution of dopant atoms and codoping of DMS. The results show that stability of the ferro- and antiferromagnetic (FM and AFM) states in DMS strongly correlates with the occupation and energy position of 3D-dopant bands. Adequacy of the double exchange and superexchange mechanisms for explanation of the FM–AFM competition is discussed.

Within the density-functional theory, fully relativistic calculations of electron and optical spectra in chromium disilicide have been performed. CrSi2 is found to be an indirect-gap semiconductor; pressure therefore has a subtle effect on the gap. The calculated electronic structure is compared with experimental data and previous band calculations.

Within the density-functional theory, including its local spin-density approximation, the fully relativistic calculations of electron, optical and magneto-optical spectra in some half-metallic ferromagnets and uranium monochalcogenide have been performed. An increase in the magneto-optical Kerr effect in half-metallic magnets is closely related to such factors as the spin-orbit exchange splittings and the plasma frequency. At the same time in the usual ferromagnets the peculiarities of band structure lead to anomalies in the conductivity tensor at energies close to the spin-orbit splitting.

The extreme ultraviolet (EUV) optical constants ( ) and ( ) of amorphous carbon were determined on the basis of transmission measurements at =18-450 eV, the first-principles calculation of the dielectric tensor at < 25 eV, and the Kramers-Kronig calculation of ( ). Our optical constants generally agree with the CXRO data, excluding the vicinity of the K-edge. First-principles analysis shows that two thresholds of absorption (at 284 eV and 291 eV) f ound in the present study are caused, respectively, by the - and - bonds. Their weights are controlled by an orientation of graphene sheets in a-carbon. Keywords: optical constants, anisotropic EUV absorption, electronic structure, graphene sheets. 1. INTRODUCTION. Analysis of carbon-based materials is important for many ecological, biological, and industrial applications. Electron energy loss spectroscopy (EELS) and near edge X-ray absorption fine structure spectroscopy (NEXAFS) provide valuable information about the arrangement and bonding of atoms, as well as about the electronic structure of carbon materials. Numerous examples of such investigations can be found in Refs. [1-3]. In these investigations the attention of researchers is focused on the shape of the carbon K-edge, while the absorption spectrum in a wide energy region, as well as the optical constants, remain unstudied. A different situation takes place for the applications of carbon-based materials in soft X-ray multilayer optics. In this case both optical constants ( ) and ( ), which characterize the complex refractive index n( )=1- ( )+i ( ), are important for multilayer design. In the present study we concentrated on the measurements of the optical constants of amorphous carbon (a-carbon). This material is widely used in soft X-ray multilayer optics at short wavelengths ( =4.4-6.0 nm) because of its transparency and low roughness. In particular, the highest normal incidence reflectivity 15 % has been obtained at these wavelengths for a Co-C multilayer mirror [4]. To further improve multilayer optics based on a-C, precise information about its ( ) and ( ) is required. Currently available optical constants of a-carbon are only those from the atomic scattering factors of elements [5]. Despite many advantages of the CXRO data [5], they are not precise near the absorption edges, where the effect of interatomic bonding is of importance. This fact is disappointing, as the working interval of reflective multilayers is normally placed just below the absorption edge. The present study provides the optical constants of amorphous carbon in a wide EUV region from 40 eV to 450 eV. The determination of ( ) and ( ) is based on our transmission measurement, which is supplemented by the first-principles calculation of the dielectric tensor at 25 eV. Particular attention is given to the spectral region near the K-edge of carbon. To interpret our transmission spectra in this region, we invoke the results of our first-principles calculation that allows connection of the shape of the absorption K-edge with the atomic bonding in a-carbon.

Influence of high magnetic fields and pressure on band structure of FeSi has been studied by the full-potential LMTO–ASA method. It is found that the semiconducting ground state of FeSi is stable in the wide volume range of ±15% of V / V exp . At the same time, as follows from the LSDA calculations, the applied external magnetic fields induce the metallic magnetic state. At low fields our results agree with the measured magnetization. There is steep increase of calculated magnetization at high critical field H cr = 170 T (itinerant metamagnetic transition).

Wurtzite (Ga,Mn)N epilayers were grown by plasma‐assisted molecular beam epitaxy. Mn incorporation strongly depends on growth conditions. Infrared optical absorption shows absorption bands related to neutral Mn acceptor A0 at 1.412 eV and 1.43 eV. Magnetic circular dichroism spectroscopyat the band gap edge, in agreement with magnetization data, exhibits temperature and magnetic field dependence revealing paramagnetic properties of Mn‐doped GaN.

Within the density-functional theory approach we have carried out fully relativistic calculations of the conductivity tensor, the Kerr rotation and ellipticity for PtMnSb, PdMnSb and NiMnSb compounds. Our calculations successfully reproduced the huge Kerr effect for PtMnSb and give the correct positions of the main features for the other compounds. The origins of the main peculiarities are discussed.

We performed magnetoresistance measurements of Fe 0.2 Co 0.8 Si and CoSi single crystals in the temperature range 4.2–60 K under magnetic fields up to 14 T. The transeverse and longitudinal magnetoresistance of Fe 0.2 Co 0.8 Si show the same magnetic field dependence, while the transverse magnetoresistance of CoSi is quite larger than the longitudinal one at the same magnetic field. These results are discussed in connection with their magnetic properties.

We studied trends in ab initio electronic structure, spin moments, orbital moments and magneto-optical (MO) properties of MPt 3 compounds. Calculated quantities agree well with existing experimental data. It was found that values of local orbital moments are closely connected with the predominant spin character of the electronic states near the Fermi energy ( E F ). Features of the MO spectra are primarily defined by the absorptive off-diagonal conductivity σ 2, xy ( ω ).

The band structures of both paramagnetic and antiferromagnetic phases were calculated in the framework of local density (or spin density) approximations of the exchange-correlation potential. In order to compute the antiferromagnetic phase of Cr the perfect nesting model was assumed. These calculations were performed as a function of the lattice parameter and also self-consistently using the linear hybridised KKR method. The ground-state and quasi-particle properties are discussed in comparison with the suitable experimental data. The pressure dependence of the magnetic moment, the nesting wave vector, the antiferromagnetic gap and the Fermi surface extremal cross sections are also discussed.

The band structure of the paramagnetic phase of the stoichiometric intermetallic compound Pt3Fe was calculated self-consistently using the linearised hybridised KKR scheme in the framework of the local density approximation of the exchange-correlation potential. The results of the band-structure calculations are discussed in connection with the unusual antiferromagnetic ordering in this compound near stoichiometric composition. Nesting-type features are found at the Fermi surface of the paramagnetic phase. The calculation of the static susceptibility function chi (q) demonstrates the existence of peaks for the q vectors corresponding to antiferromagnetic structures.

The results of band structure calculations for HCP Co in ferromagnetic and paramagnetic phases are presented together with a self-consistent FCC Co band structure. These calculations were performed by means of a linearised KKR method (model Hamiltonian) for lattice constants appropriate to atmospheric pressure and 290 kbar. On the basis of the calculations the authors offer a new model for the Fermi surface of ferromagnetic HCP Co. The stability of the paramagnetic state is studied for both HCP and FCC phases under pressure. Also, the results of band structure calculations are analysed by comparing the theoretical band structure with experimental measurements of the photoelectron spectrum. The calculated joint density of states for spin sub-bands in the ferromagnetic phase of HCP Co has shown agreement between the experimental data and the theoretical predictions of peculiarities in the energy dependence of the optical conductivity.