Search

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.

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.

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).

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.