Half Metallic Ferromagnetism and Transport Properties of Zinc Chalcogenides ZnX2Se4 (X = Ti, V, Cr) for Spintronic Applications

In ferromagnetic semiconductors, the coupling of magnetic ordering with semiconductor character accelerates the quantum computing. The structural stability, Curie temperature (Tc), spin polarization, half magnetic ferromagnetism and transport properties of ZnX2Se4 (X = Ti, V, Cr) chalcogenides for spintronic and thermoelectric applications are studied here by density functional theory (DFT). The highest value of Tc is perceived for ZnCr2Se4. The band structures in both spin channels confirmed half metallic ferromagnetic behavior, which is approved by integer magnetic moments (2, 3, 4) μB of Ti, V and Cr based spinels. The HM behavior is further measured by computing crystal field energy ΔEcrystal, exchange energies Δx(d), Δx (pd) and exchange constants (Noα and Noβ). The thermoelectric properties are addressed in terms of electrical conductivity, thermal conductivity, Seebeck coefficient and power factor in within a temperature range 0–400 K. The positive Seebeck coefficient shows p-type character and the PF is highest for ZnTi2Se4 (1.2 × 1011 W/mK2) among studied compounds.

Magnetism at Finite Temperatures

Thermal properties of magnets are dominated by low-lying excitations, perused systematically. Magnon spectra of elementary metals and compounds are obtained theoretically and compared with experimental data. Spin fluctuations are discussed in mean-field theory to obtain ab initio estimates of ordering temperatures for a multitude of magnetic systems. The free energy is connected with dynamic susceptibility which supplies a solid basis for the magnetic phase of ferromagnetic compounds. Methods derived to obtain Heisenberg exchange constants from first-principle calculations are compared with experimental data. Magnetic skyrmions enrich the field of magnetism and are of possible use for data technology applications. Several cases are discussed and classified showing theoretical and experimental data. For high temperatures the disordered local moment picture supplies an alternative theory for magnetism where the coherent-potential approximation is used to solve the electronic-structure problem in an alloy analogy. The basic theory is presented and discussed together with experimental data.

Towards Kitaev spin liquid in 3d transition metal compounds

This paper reviews the current progress on searching the Kitaev spin liquid state in 3[Formula: see text] electron systems. Honeycomb cobaltates were recently proposed as promising candidates to realize the Kitaev spin liquid state, due to the more localized wavefunctions of [Formula: see text] ions compared with that of [Formula: see text] and [Formula: see text] ions, and also the easy tunability of the exchange Hamiltonian in favor of Kitaev interaction. Several key parameters that have large impacts on the exchange constants, such as the charge-transfer gap and the trigonal crystal field, are identified and discussed. Specifically, tuning crystal field effect by means of strain or pressure is emphasized as an efficient phase control method driving the magnetically ordered cobaltates into the spin liquid state. Experimental results suggesting the existence of strong Kitaev interactions in layered honeycomb cobaltates are discussed. Finally, the future research directions are briefly outlined.

Anion exchange extraction of tallium (III) and mercury (II) complex salts and application of the procedure to extraction-photometric determination of the microquantities of mercury (II)

The goal is to study the anion-exchange extraction of complex thallium (III) and mercury (II) halides (chlorides, bromides, iodides) by a method of a competing intermediate ion using the anions of various dyes — methyl orange, sodium picrate, 2,4-dinitrophenol, methyl red. Mercury (II) and thallium (III) are poisons of high toxicity. The developed method was used to study the anion-exchange extraction of acidocomplexes A solution of methyl orange trinonyloctadecylammonium (TNODA) in toluene was used as an extractant. The method provides determination of mercury (II) with an accuracy of ±2% when the concentration in the initial solution ranges within 2 – 8 × 10–8 mol/liter. It is shown that the values of the exchange constants for the same metal are larger for iodide complexes than for bromide and chloride ones. The extractability of metal halide complexes is mainly determined by their mass. Anions with a large mass have a large surface area, a low charge density, and are weakly hydrated, and thus are better extracted. The results of anion-exchange extraction were used to develop a procedure for the extraction-photometric determination of mercury (II) in granosan (ethylmercury chloride a prohibited insectofungicide of the 1st hazard class) the illegal use and storage of which could be a source of mercury pollution of groundwater in a number of regions of the Republic of Belarus. The relative error of determination does not exceed ±2%.

Evaluation of properties, processes and modes of acid-base conditions on sod-podzolic soils

The paper offers an assessment of the acid-base state of soils, accounting for the interrelationships of properties, processes and modes. The information content of the assessment of the fractional composition of acid-base systems, the kinetics of the processes, the suspension effect, the buffer capacity in different pH ranges, the depositing ability of soils to ions that determine their acid-base state is shown. The optimal indicators of the acid-base state of soils are estimated using the feedback principles: introduction of elements into the soil suspension - analysis of the response of plants developing on this suspension by the parameters of photosynthesis - search for the extremum. It is shown that the change in soil acidity is largely due to the processes of complex formation, the effects of protonation and hydrate formation of complexes of organic ligands and polyvalent cations. The expediency of using water-soluble organic substances of decomposing plant residues to increase the solubility of CaCO3 and purposefully change the exchange constants H+, Fe2+, Mn2+, A13+ from the Soil Absorption Complex to the Ca2+ ion is shown. Shown that increased sod soil formation process leads to a migration of Ca, Mg, and K to the arable layer from underlying layers. Ca, Mg and K also transition from a non-exchange state to the exchange state that allows for an increase in the time between repeated rounds of liming of sod-podzolic soils. Keywords: SOIL ACIDITY, SOIL PROPERTIES PROCESSES AND MODES

An ab initio study of the magnetic properties of strontium hexaferrite

The magnetic properties of $${\text{SrFe}}_{12}{\text{O}}_{19}$$ SrFe 12 O 19 , a paradigmatic hexaferrite for permanent magnet applications, have been addressed in detail combining density functional theory including spin–orbit coupling and a Hubbard U term with Monte Carlo simulations. This multiscale approach allows to estimate the Néel temperature of the material from ab initio exchange constants, and to determine the influence of different computational conditions on the magnetic properties by direct comparison versus available experimental data. It is found that the dominant influence arises from the choice of the Hubbard U term, with a value in the 2–3 eV range as the most adequate to quantitatively reproduce the two most relevant magnetic properties of this material, namely: its large perpendicular magnetocrystalline anisotropy and its elevated Néel temperature.

Магнитные, электронные и оптические свойства тетраборатов NiB-=SUB=-4-=/SUB=-O-=SUB=-7-=/SUB=- и CoB-=SUB=-4-=/SUB=-O-=SUB=-7-=/SUB=- в трех структурных модификациях

Within a framework of the density functional theory using the VASP software package, physical properties of tetraborate compounds NiB4O7 and CoB4O7 in three structural modifications with space symmetry groups of Pbca, Cmcm and P6522 were calculated. The dependences of the enthalpy of compounds on pressure in studied structural modifications are calculated. The calculated electron densities of states and band structures showed that studied compounds in all considered modifications are dielectrics with a band gap of 3-4 eV. The calculation of the magnetic exchange constants was carried out in the Heisenberg model, which showed qualitative agreement with experiment.