Pressure effect on electronic structure and magnetic properties of MB₆ and MB₁₂ borides

Theoretical and experimental studies of the pressure effect on electronic structure and magnetic properties of MB₆ and MB₁₂ borides are carried out to determine the electronic ground states and interactions responsible for the bulk and magnetic properties of these compounds. The band structure and total energy E were calculated ab initio for a number of atomic volumes, providing the equation of states, E(V), bulk moduli B, magnetic moments and susceptibilities. The temperature and pressure dependencies of magnetic susceptibility were also experimentally studied for a number of borides using a pendulum-type magnetometer. In semimetallic EuB₆ the paramagnetic Curie temperature is found to be increasing with pressure, dθ/dP = 0.44 ± 0.03 K/kbar, whereas in closely related GdB₆ compound the pressure effect is lower in magnitude but opposite in sign: dθ/dP = –0.17 ± 0.03 K/kbar. The peculiar details in electronic structures are found to be responsible for distinctions in magnetic ordering and the pressure effects on indirect f−f interactions

ULTRASONIC STUDIES OF CONDUCTIVITY OF SUPERCONDUCTORS

La mesure de la constante complexe de propagation du son transversal au voisinage de la temperature critique permet de déterminer les parties réelle et imaginaire de la conduction d'un supraconducteur et leur anisotropie.The measurement of the complex constant of the transverse sound propagation near Tc permits the real and imaginary parts of the superconductor conductivity and their anisotropy to be found

NONLINEAR ACOUSTIC PROPERTIES OF CONDUCTION ELECTRONS

On a étudié expérimentalement différents types de non-linéarités se présentant dans les états normal et supraconducteur d'un métal sous l'effet du pompage ultra-sonore.Various types of nonlinearities appearing in the normal and superconducting States of the metal due to ultrasonic pumping are studied experimentally

Electronic structure and bulk properties of MB₆ and MB₁₂ borides

Ab initio band structure calculations have been carried out for higher boridesMB6 andMB12. High precision measurements of the elastic constants were performed for ZrB₁₂, HoB₁₂, ErB₁₂, TmB₁₂, LuB₁₂, YB₆ and LaB₆ compounds at low temperatures. The bulk properties of the borides have been 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 bulk moduli are found to be higher for MB₁₂ with increased filling of the conduction band (ZrB₁₂, HfB₁₂, UB₁₂), comparatively to M³+B₁₂ compounds. The total energy calculations for different magnetic configurations in YbB₁₂ point to a possibility of antiferromagnetic coupling between Yb³⁺ ions