Kobzar I. Magnetoelastic properties of narrow-band systems based on 4f and 3d metals.

The thesis is devoted to the investigation under hydrostatic pressure of the peculiarities of magnetic susceptibility for narrow-band metallic systems, which are based on 4f- and 3d-metals. The dependences of magnetic properties on temperature, total pressure, as well as changes in the composition of systems are studied. Experimental and theoretical studies of the influence of pressure on magnetic properties and the electronic structure of metal Gd were carried out to demonstrate the nature of magnetic ordering and interaction between localized 4f moments. One of the important results of the work is the confirmation of existence of the intermediate valence state of the ytterbium ion, v~2.8, in the YbB4 compound, based on the magnitude and positive sign of the effect of pressure on the observed susceptibility. The correlations between the electronic states of RT4Al8 systems and their magnetic and magnetoelastic properties were established. The experimental values of the magnetovolume effect, obtained in the work for YCo2 at the finite temperatures, can be used in analyzing the properties of two-sublattice RCo2 magnets to account for the dominant contribution to the magnetism in these systems of the interactions between the 3d-states of cobalt. Investigation of the magnetic susceptibility under pressure of helium up to 2 kbar, carried out at fixed temperatures of 78 and 300 K, revealed a large effect of pressure on the magnetic susceptibility of FeSe and FeTe.