Pressure effect on magnetic susceptibility and exchange interactions in GdMx (x = 1, 2, 3, 5) systems

Effect of pressure on electronic structure and magnetic properties of GdMx (x = 1, 2, 3, 5) systems is studied experimentally and theoretically. By employing the ab initio electronic structure calculations, the magnetic susceptibilities, saturation moments, exchange parameters, magnetic ordering temperature and their pressure derivatives are evaluated and appeared to be consistent with available experimental data. The obtained results are expected to promote further advance in the theory of magnetic ordering in rare-earth systems

Pressure effect on magnetic properties of gadolinium in paramagnetic state

In this report we are mostly focused on refinement of the experimental dependence of the magnetic transition temperature TC on pressure under pure hydrostatic (gaseous) conditions. Unlike previously used methods, we employed a new procedure, based on the measurement of pressure effect on the dc magnetic susceptibility of Gd in the paramagnetic state at temperatures above TC. The dc paramagnetic susceptibility of Gd was measured in the temperature range of 295−365 K and under hydrostatic pressure up to 0.16 GPa, yielding values of the paramagnetic Curie temperature Θ and its pressure derivative. Also we explored a possibility to describe pressure effects on magnetism of Gd within simple mean-field approaches, which are based on ab initio electronic structure calculations. Based on the results of electronic structure calculations within the density functional theory, the experimental behavior of Θ under pressure was described in the framework of mean-field like approach.Проведены измерения парамагнитной восприимчивости Gd в интервале температур 295−365 K в условиях гидростатического сжатия до 0.16 GPa, что позволило получить значения парамагнитной температуры Кюри Θ и ее производной по давлению. Основываясь на результатах расчетов электронной структуры с использованием теории функционала плотности, было исследовано поведение Θ под давлением в рамках теории среднего поля. С этой целью были вычислены эффективная восприимчивость зонных d-электронов и соответствующие обменные интегралы как функции параметров решетки.Було виміряно парамагнітну сприйнятливість Gd в інтервалі температур 295−365 K в умовах гідростатичного тиску до 0.16 GPa, що дозволило отримати значення парамагнітної температури Кюрі Θ та її похідної за тиском. На основі результатів розрахунків електронної структури з використанням теорії функціонала густини було досліджено поведінку Θ під тиском у рамках теорії середнього поля. З цією метою були обчислені ефективна сприйнятливість зонних d-станів і відповідні обмінні інтеграли як функції параметрів ґратки

Magnetovolume effect in Ce(Ni1−xCux)₅ alloys

Magnetic susceptibility χ of the isostructural Ce(Ni1−xCux)₅ alloys (0 ≤ x ≤ 0.9) was studied as a function of the hydrostatic pressure up to 2 kbar at fixed temperatures of 77.3 and 300 K, using a pendulum-type magnetometer. A pronounced pressure effect on χ is found to be negative in sign and strongly (non-monotonously) dependent on the Cu content, showing a sharp maximum at x ≅ 0.4. The experimental results are discussed in terms of the valence instability of Ce ion in the studied alloys. For the reference CeNi₅ compound the main contributions to χ and their volume dependence are calculated ab initio within the local spin density approximation (LSDA), and appeared to be in close agreement with experimental data

Pressure effect on magnetic properties of valence fluctuating system Ce(Ni₁₋xCux)₅

Magnetic susceptibility χ of the isostructural Ce(Ni₁₋xCux)₅ alloys (0 ≤ x ≤ 0.9) was studied as a function of the hydrostatic pressure up to 2 kbar at fixed temperatures 77.3 and 300 K. A pronounced pressure effect on susceptibility is found to be negative in sign and nonmonotonously dependent on the Cu content, showing a sharp maximum at x 0.4. The experimental results are discussed in terms of the valence instability of Ce ion in the studied alloys. For the reference CeNi5 compound the main contributions to χ and their volume dependence are calculated ab initio within the local spin density approximation, and appeared to be in close agreement with experimental data

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

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