[en] Epitaxially manufactured structures grown pseudomorphically on suitable substrates provide a way to stabilise non-equilibrium structures of materials. This includes grown films which posses a large lattice misfit between substrate and film material under equilibrium conditions, but also if the structure grown differs from the equilibrium structure of the bulk film material. Large misfits do not necessarily mean large lateral stress. Theory can help to predict e.g. geometry, stresses and magnetic properties of pseudomorphically grown metal films. In this work, we considered the epitaxial Bain path of elemental uranium, which provides a reasonable description of tetragonally distorted films on substrates. We employed density functional calculation in the implementation of the full potential local orbital program package FPLO. We found three meta-stable tetragonal phases, in addition a ferromagnetic state close to the fcc phase.

No abstract available

[en] We performed full-potential density functional theory (DFT) calculations on 5f inter-metallic compounds, which have either tetragonal (FD3M, FM3M, I4/MMM) or hexagonal (P6/MMM) symmetry. We used the local spin density approximation (LSDA) in a full relativistic implementation to calculate their magnetic properties. Since it is a known error of LSDA to underestimate the orbital moment, we applied orbital polarisation corrections (OPC) to these 5f states. The magnetocrystalline anisotropy energy (MAE) is connected with orbital moments. Hence OPC affects the MAE. Comparing our results with available experimental data in literature, we find a systematic improvement of orbital moments and MAE with applied OPC. Nevertheless these estimates may be seen as an upper bound.

No abstract available

[en] We have investigated the spontaneous anisotropic magnetostriction of element hcp Gd metal in two different approximations to density functional theory, the local spin density approximation (LSDA) and the so-called LSDA+U. As a rough model for the paramagnetic state with large persisting 4f-moments several static AFM arrangements were used. The obtained value of spontaneous volume magnetostriction is reasonable, but the sign of the anisotropic magnetostriction is different in LSDA and LSDA+U

[en] The compound LaCrSb₃ is a non-collinear ferromagnet with a spin reorientation at T_sr∼95 K. Coexistence of itinerant and localized spins at one and the same Cr site was suggested to explain the experimental findings. Here, arguments against this model are provided on the basis of electronic structure calculations and re-considered experimental information. An alternative model is proposed

[en] The appearance of oxygen vacancies in a surface of strontium titanate has been recently identified to be a likely reason for the formation of a two-dimensional electron gas close to the surface. Lately the first SARPES measurements on these surfaces unveiled an interesting spin texture which shows besides the expected Rashba effect a huge spin splitting that can not be attributed to spin-orbit interaction. Employing density functional theory we therefore examined oxygen deficient slabs and found that indeed magnetism is capable of explaining the measured spin splittings. Moreover we obtain a very rich spin texture where we find not only rotating spins due to the Rashba interaction, but a very complex spin structure most likely caused by an interplay of orbital and spin degrees of freedom.

[en] To analyse the charge dynamics of La,Sr-bilayer manganites we performed angle resolved photoemission measurements on (La_1-xPr_x)_1.2Sr_1.8Mn₂O₇ single crystals. The spectra are compared to a tight-binding Wannier model. The measured bilayer splitting is much smaller than the calculated one, indicating a strongly reduced hybridization between the bilayer-planes in the real material. Further the spectral function exhibits fingerprints of a periodic perturbation with an interaction strength of around 400 meV. A possible origin of such a perturbation are CE-type charge-order fluctuations.

[en] Recently, substitution derivatives of the intermetallic compound RuIn_3-xA_x (A = Sn,Zn) have been shown to exhibit relatively high Seebeck coefficients. Substitution by Sn results in n-type behavior while p-type is the norm for substitution of In by Zn. We discuss in detail the electronic structure of the parent compound and the substitution derivatives obtained from density functional theory based calculations using the Full Potential Local Orbital code. The substitution effects have been studied using three different approximations: the simple virtual crystal approximation, the ordered supercell approach and the disordered coherent potential approximation. Both Sn and Zn prefer different site symmetry positions in the unit cell. While the parent compound RuIn₃ is a semiconductor, the substitution derivatives are not. For small doping concentrations, we observe a rather rigid-band-like behavior due to the parabolic nature of the bands forming the valence band maximum and the conduction band minimum. Transport properties calculated using the semi-classical Boltzmann transport equations based on the constant scattering approximation are consistent with the experiments.

[en] In a joint experimental and theoretical study we investigate the crystal structure of the Fe pnictide compounds SrFe₂As₂ under applied hydrostatic pressure. Applying high pressure X-ray diffraction, for a critical pressure of about 10 GPa we observe a sudden collapse of the tetragonal c axis, accompanied by a small expansion of the basal plane. This results in a drastic reduction of the c/a ratio and a significant decrease of the unit cell volume. This tetragonal collapse is well described by DFT band structure calculations and can be assigned to the formation of an additional As-As bond along the tetragonal c axis.