Ab initio band structure calculations are carried out for the higher borides MB 6 and MB 12 . Highprecision measurements of the elastic constants are performed for the compounds ZrB 12 , HoB 12 , ErB 12 , TmB 12 , LuB 12 , YB 6 and LaB 6 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, CaB 6 , SrB 6 , BaB 6 , and YbB 6 , are semiconductors with small energy gaps. The metallic MB 6 hexaborides with trivalent M atoms are found to possess larger bulk moduli values. For dodecaborides the bulk moduli are found to be higher for MB 12 with increased filling of the conduction band ͑ZrB 12 , HfB 12 , UB 12 ͒ in comparison with M 3+ B 12 compounds. The total energy calculations for different magnetic configurations in YbB 12 point to the possibility of antiferromagnetic coupling between Yb 3+ ions.

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The temperature dependences of the magnetic susceptibility χ and its anisotropy Δχ=χ∥−χ⊥ have been measured for hexagonal single crystals of transition-metal diborides MB2 (M=Sc,Ti,V,Zr,Hf) in the temperature interval 4.2–300K. It is found that the anisotropy Δχ is weakly temperature-dependent, a nonmonotonic function of the filling of the hybridized p−d conduction band, and largest for group-IV transition metals. First-principles calculations of the electronic structure of diborides and the values of the paramagnetic contributions (spin and Van Vleck) to their susceptibility show that the behavior of the magnetic anisotropy is due to the competition between Van Vleck paramagnetism and orbital diamagnetism of the conduction electrons.

A study is made of the electronic structure and magnetic properties of RN5−xCux alloys (R=Y, La, Ce). The influence of substitution of nickel by copper on the features of the band structure and behavior of the magnetic susceptibility of these alloys is investigated. An analysis is made of the electronic states and interactions responsible for the magnetic properties of RNi5−xCux alloys.

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The effect of pressure on the electronic structure and magnetic properties of the compounds YNi 5 , LaNi 5 , and CeNi 5 is studied. Large magnetovolume effects of magnitude d ln / d ln V Ӎ 4 -7 are found for the magnetic susceptibility of these systems at low temperatures. Experimental data and "first principles" calculations of the electronic structure and paramagnetic contributions to the susceptibility indicate that YNi 5 , LaNi 5 , and CeNi 5 are close to a quantum critical point. It is found that the van Vleck orbital contribution to the magnetic susceptibility is 15-20% in these exchange-enhanced paramagnetic materials and should be taken into account in analyzing experimental data on and d ln / d ln V. Calculations of the magnetic-field induced moments for atoms in the unit cell of YNi 5 reveal an inhomogeneous distribution of the magnetization density and a nontrivial competition between the spin and orbital moments.

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