ИСТИНА

For centuries, iron has been the core of various construction materials ranging from cast iron to elaborate still and modern alloys. Nowadays, this metal is accepting another role, since properties of Fe-based compounds give rise to new areas of their applications as functional materials. The discovery of Fe-based superconductors in 2008 [1] has renewed keen interest in functional properties of multifarious compounds of iron, including oxides, chalcogenides, pnictides, and intermetallics. In this paper, we will discuss several types of these compounds. Iron-rich ternary tellurides, Fe3ETe2, feature a layered character of crystal structures pertinent to Fe-based superconductors but differ by having a number of Fe-Fe bonds, leading not only to metallic behavior but also to peculiar magnetic structures responsible for sizable magnetocaloric effect and giant magnetocrystalline anisotropy. In FeGa3-based solid solutions, strong d¬-p¬ interactions between iron and gallium open the band gap in the electronic structure near the Fermi level. Depending on the nature of substituting element and concentration of valence electrons, these solid solutions display different properties ranging from quantum criticality to interplay between localized and itinerant magnetism and to high thermoelectric efficiency. In more complex crystal structures as Fe32+xGe33E2, where recurrent intergrowth of blocks takes place, the interaction of spins of several independent iron atoms results in a complex antiferromagnetic-like ordering with non-trivial physics that still awaits detailed investigations.