[en] Electronic structure calculations are carried out for the ferromagnetic GdM₂ compounds (M=Mg, Al, Fe, Co, Ni, Rh, Ir, Pt). By using the calculated susceptibilities, densities of electronic states, and exchange parameters, the Curie temperatures were evaluated for these compounds in the framework of a modified molecular-field approach. The calculated magnetic ordering temperatures appeared to be in improved agreement with experimental data, in contrast to the results obtained within a conventional mean-field theory

[en] The concentration of carriers in LuB₁₂ is evaluated theoretically by applying ab initio FP-LMTO calculations. Theoretical results are found to be in agreement with high precision measurements of the Hall R_H(T) coefficient which were carried out on single crystals of the rare earth dodecaborides RB₁₂ (R = Ho, Er, Tm, Lu) at temperatures 1.8-300 K. A nature of the antiferromagnetic ordering in RB₁₂ is investigated within the RKKY-like model, which was supplemented by comprehensive electronic structure calculations for paramagnetic, ferromagnetic and antiferromagnetic phases.

[en] Ab initio band structure calculations are carried out for the higher borides MB₆ and MB₁-2. High-precision measurements of the elastic constants are performed for the compounds ZrB₁₂, HoB₁₂, ErB₁₂, TmB₁₂, LuB₁₂, YB₆ and LaB₆ at low temperatures. The bulk properties of the borides are analyzed on the basis of the calculated equations of states and balanced crystal orbital overlap populations. Our calculations indicate that hexaborides with divalent metals, CaB₆, SrB₆, BaB₆, and YbB₆, are semiconductors with small energy gaps. The metallic MB₆ hexaborides with trivalent M atoms are found to possess larger bulk moduli values. For dodecaborides the bulk moduli are found to be higher for MB₁₂ with increased filling of the conduction band (ZrB₁₂, HfB₁₂, UB₁₂) in comparison with M³⁺B₁₂ compounds. The total energy calculations for different magnetic configurations in YbB₁₂ point to the possibility of antiferromagnetic coupling between Yb³⁺ ions

[en] The electronic structures of RB₆, RB₁₂ and RB₂C₂ borides are studied ab initio by using the full-potential linear Muffin-Tin orbital method. This study includes the promising materials for spin electronics with reported high temperature ferromagnetism, namely, doped divalent hexaborides CaB₆, SrB₆, BaB₆, and the CaB₂C₂ compound, as well as Kondo semiconductors, SmB₆ and YbB₁₂. For CaB₆ and SrB₆ a semiconducting band structure has been obtained, whereas a semimetallic ground state is revealed for CaB₂C₂ and doped hexaborides. For YB₆, LaB₆, CaB₂C₂ and the semimetallic Ba_1-xLa_xB₆ alloys we have performed spin-polarized band structure calculations in an external field to evaluate the induced spin and orbital magnetic moments. These calculations indicate a feasibility of the field-induced weak ferromagnetic phase in CaB₂C₂ and the La doped hexaborides. The LSDA and GGA calculations for different spin configurations of YbB₁₂ point to a possibility of antiferromagnetic coupling between Yb ³⁺ ions. For SmB ₆ and YbB ₁₂ our LSDA, GGA, and LSDA+U calculations have not revealed the hybridization gap for configurations with trivalent Sm³⁺ and Yb³⁺. (copyright 2006 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

[en] The bulk and magnetic properties of MB₆ and MB₁₂ were investigated on the basis of first principles electronic structure calculations. The elastic constants were measured for ZrB₁₂, HoB₁₂, ErB₁₂, TmB₁₂, LuB₁₂, YB₆ and LaB₆ compounds at low temperatures. The calculated equations of states and balanced crystal orbital overlap populations have allowed to analyse bonding and magnetic properties of MB₆ and MB₁₂