Новые публикации

https://doi.org/10.3390/ma16062318

Copper ferrite is of great interest to researchers as a material with unique magnetic, optical, catalytic, and structural properties. In particular, the magnetic properties of this material are structurally sensitive and can be tuned by changing the distribution of Cu and Fe cations in octahedral and tetrahedral positions by controlling the synthesis parameters. In this study, we propose a new, simple, and convenient method for the synthesis of copper ferrite nanoparticles using a strongly basic anion-exchange resin in the OH form. The effect and possible mechanism of polysaccharide addition on the elemental composition, yield, and particle size of CuFe₂O₄ are investigated and discussed. It is shown that anion-exchange resin precipitation leads to a mixture of unstable cubic (c-CuFe₂O₄) phases at standard temperature and stable tetragonal (t-CuFe₂O₄) phases. The effect of reaction conditions on the stability of c-CuFe₂O₄ is studied by temperature-dependent XRD measurements and discussed in terms of cation distribution, cooperative Jahn–Teller distortion, and Cu²⁺ and oxygen vacancies in the copper ferrite lattice. The observed differences in the values of the saturation magnetization and coercivity of the prepared samples are explained in terms of variations in the particle size and structural properties of copper ferrite.

https://doi.org/10.1016/j.omtn.2023.03.015

https://doi.org/10.1134/S0965544123020196

Potentialities of magnetic resonance imaging (MRI) in petroleum research are analyzed. Major attention is paid to technical features of the method as applied to oil extraction and preparation. Available published data are systematized. Four key directions of MRI, which undergo active development now, are distinguished: oil in a porous matrix; oil interfaces; destabilization of petroleum systems; transport of crude oils and petroleum systems. Key studies in this field are considered, essential points reflecting the MRI efficiency are presented, and the range of problems that can be solved using MRI, including prospects for further expansion of the application fields, is outlined. The possibilities of studying the morphological, structural, and dynamic aspects of the interaction of crude oils with the environment and the phase behavior of oils under the conditions of intense external actions are discussed. The review favors expansion of the experimental potential of specialists in the field of oil extraction, preparation, and refining, and also in the adjacent fields of physical and colloidal chemistry, chemistry of surface phenomena, and macromolecular chemistry.

https://doi.org/10.1103/PhysRevB.107.115413

Features of the spin dynamics in ensembles of interacting (FH-chem) and weakly interacting (FH-coated) magnetic ultrasmall ($⟨d⟩\sim 2$ nm) ferrihydrite nanoparticles have been explored. The dc and ac magnetic susceptibilities $[{\chi }^{\prime }\left(T\right)$ and ${\chi }^{\text{'}\text{'}}\left(T\right)]$ of the investigated samples have been thoroughly measured in a weak magnetic field (2 Oe) around the temperatures of superparamagnetic blocking of the nanoparticle magnetic moments (19 and 50.4 K for FH-coated and FH-chem, respectively, according to the dc magnetization data). It has been shown that the magnetic interactions between nanoparticles induce the formation of the cluster spin-glass state below the superparamagnetic blocking temperature ($T_g=18$ and 49.5 K for FH-coated and FH-chem, respectively). It has been found that coating of nanoparticles increases the critical scaling index from $z\nu =5.9$ (FH-chem) to $z\nu =8.0$ (FH-coated). This indicates a general slowdown of the dynamics of correlated spins, which is also expressed as an increase in relaxation time ${\tau }_0$ after switching on the interparticle interactions. We attribute this phenomenon to a consequence of a change in the volume of correlated spins with the increasing size of a cluster of interacting nanoparticles. It has been demonstrated using the simulated ${\chi }^{\text{'}\text{'}}\left(T\right)$ dependence that the dissipation of the magnetic energy occurs in two independent stages. The first stage is directly related to the blocking of the nanoparticle magnetic moments, while the second stage reflects the spin-glass behavior of surface spins and depends strongly on the intensity of the interparticle interactions.

https://doi.org/10.1016/j.mtla.2023.101759

Magnetic and magneto-optical properties of cobalt nanoparticles (Co-NPs) dispersed in a transparent dielectric SiO₂ and semiconductor ZnO matrices have been investigated. Field and temperature dependences of the samples magnetization showed the typical behavior of an ensemble of superparamagnetic particles with a blocking temperature near and below room temperature. The spectroscopy of magnetic circular dichroism (MCD) in the visible and near-infrared light ranges has revealed a significant difference between the behavior of the Co-NPs and a solid Co film. It has been found that the MCD spectrum shape for the Co-NPs does not depend on the matrix type. The room temperature magneto-optical activity of the Co-NPs in the different matrices has been estimated as an indicator for practical applications.

https://doi.org/10.1016/j.physb.2023.414821

Effect of substitution Dy by Ho on the magneto-electric behavior of the compound Dy_0.8Ho_0.2MnO₃ was investigated by the different methods of polarized and classical neutron diffraction and macroscopic methods. It is shown that substitution by Ho of 20% on the position of Dy do not change overall crystal symmetry of compound. It remains of Pbnm type down to the very low temperatures. Magnetic ordering, its temperature and field evolution was determined by the use of single crystal neutron diffraction and magnetization measurements. Chiral type of magnetic structure on Mn subsystem is confirmed below Tc ≈ 16 K. Using polarized neutron diffraction the 3-component character of rare earth magnetic ordering in Dy_0.8Ho_0.2MnO₃ in contrast to DyMnO₃ could be revealed. It was shown that doping by 20% Ho suppresses the spontaneous rare-earth ordering with its own propagation vector and provides the situation when two magnetic subsystems, manganese and rare earth ones have a coherent incommensurate spatial propagation. The influence of the external electric field on the magnetic chirality could be directly evidenced, proving strong magneto-electric coupling in multiferroic phase. The study of the electric polarization under similar temperatures and fields on the same samples provides the direct correlation between the results of the microscopic and macroscopic investigations.

https://doi.org/10.1002/adom.202203151

Artificial light fishing technology has been used in marine fisheries for thousands of years. The light source with multi-color adjustable output is expected to become a new generation of fish-attracting lamps. Herein, a new method of crystal-site engineering through reducing atmospheres is proposed for the development of Eu²⁺ doped single-phase phosphor with multi-excitation and multi-emission properties. Following this approach, the distribution ratio of Eu²⁺ at Ca²⁺ and Sr²⁺ sites in CaSrSiO₄ (CSO) can be modulated. Importantly, Eu²⁺ at both lattice sites exhibit non-interfering optical properties, CSO:Eu²⁺ phosphor realizes multi-color output from green to yellow and then to red when Eu²⁺ occupies the Sr²⁺ and Ca²⁺ sites in a relatively balanced ratio. Benefitting from the tunable color range covering the spectral sensitivity regions of most marine fishes, this phosphor may eventually be applied in futuristic innovative fish-attracting lamps.

 https://doi.org/10.3390/app13064004

A photonic topological insulator is a structure that isolates radiation in the bulk rather than at the edge (surface). Paradoxically, applications of such an insulator focus on its conducting edge states, which are robust against structural defects. We suggest a tiling photonic topological insulator constructed from identical prism resonators connected to each other. The light beam circulates inside the tiling bulk without propagation. However, we experimentally demonstrate a topologically-protected propagating state due to the disconnected faces of the edge resonators. The investigated state is robust against removing or attaching prism resonators. Moreover, the protection principle is phase-free and therefore highly scalable both in wavelength and resonator size. The tiling is suggested for active topological photonic devices and laser arrays.

https://doi.org/10.1134/S1028335822020021

A half-wave microstrip resonator design with an irregular strip conductor short-circuited to the screen by its ends has been investigated. Based on the resonances of the first two oscillatory modes of this resonator, a miniaturized second-order filter with a fractional bandwidth from 40% to 90% has been implemented, which has a wide high-frequency stopband. A prototype of the designed eight-order filter based on four dual-mode resonators with a passband center frequency of 2 GHz and a fractional bandwidth of 40% has been fabricated on an alumina substrate 45.0 × 10.5 × 1.0 mm³ in size with a permittivity of ε = 9.8. The filter frequency response slopes are extremely steepness due to two attenuation poles located on the left and right sides of the passband. The experimental characteristics of the prototype are in good agreement with the data of the numerical electromagnetic simulation of the 3D model of the filter.

https://doi.org/10.1134/S1062739122060187

The article describes the studies into the process of upward mass transfer in flotation tailings with water solutions. The swift-flowing geological process is investigated using the magnetic resonance imaging. The kinetics of water-soluble minerals as well as the structure and substance transformations in the body of tailings are studied for substantiating in-situ formation of the target concentration zones at the tailings surface.

https://doi.org/10.1134/S1063778822100398

The Monte Carlo method was used in a 2D model of the layered HTSC to calculate the magnetization curves of a granulated high-temperature superconductor for various sizes of granules. In this approach magnetization of granules alone is taken into account, while the contribution of the gaps between granules is small and neglected. The irreversibility field has been found to decrease with temperature at the fixed size of granules and increase as the granule size increases at fixed temperature. The time dependence of residual magnetization has been studied at various temperatures. The relaxation rate is shown not to depend on the granule size at low temperatures but to decrease with the increasing size (provided that the granule size is less than 3 μm) at a high temperature when the magnetic flux creep becomes of importance.

https://doi.org/10.1002/adom.202203151

Artificial light fishing technology has been used in marine fisheries for thousands of years. The light source with multi-color adjustable output is expected to become a new generation of fish-attracting lamps. Herein, a new method of crystal-site engineering through reducing atmospheres is proposed for the development of Eu²⁺ doped single-phase phosphor with multi-excitation and multi-emission properties. Following this approach, the distribution ratio of Eu²⁺ at Ca²⁺ and Sr²⁺ sites in CaSrSiO₄ (CSO) can be modulated. Importantly, Eu²⁺ at both lattice sites exhibit non-interfering optical properties, CSO:Eu²⁺ phosphor realizes multi-color output from green to yellow and then to red when Eu²⁺ occupies the Sr²⁺ and Ca²⁺ sites in a relatively balanced ratio. Benefitting from the tunable color range covering the spectral sensitivity regions of most marine fishes, this phosphor may eventually be applied in futuristic innovative fish-attracting lamps.

• https://doi.org/10.1364/OL.479431

A photonic crystal microcavity with a tunable quality factor (Q factor) has been implemented on the basis of a bound state in the continuum using the advanced liquid crystal cell technology platform. It has been shown that the Q factor of the microcavity changes from 100 to 360 in the voltage range of 0.6 V.

 http://dx.doi.org/10.2139/ssrn.4330358

The objectives of the article were to synthesize and study the properties of GdSF, to construct a phase diagram of the GdF3-Gd2S3 system, and to calculate the liquids. The GdSF compound (ST PbFCl, P4/nmm, a = 0.3832(7) nm, c = 0.6853(9) nm) has an optical band gap for a direct interband transition of 2.56 eV and is characterized by a pronounced increase in the Kubelka-Munk function in the region of this transition. Direct optical bandgap of GdSF is measured to be 2.77 eV. Two indirect bandgaps are detected to be 1.54 and 2.4 eV. Meta-GGA simulations of band structure predicting 1.481 eV direct bandgap of GdSF are in good agreement with these features of experimental absorption spectrum. To explain this complicate case, we argue that formally direct optical transitions to highly dispersive subbands contribute not to direct but to indirect bandgaps measured by Tauc analysis. The GdSF compound melts incongruently with the formation of a melt and γ-Gd2S3 compound at t = 1280 ± 2 ºС, ΔН = 40.6 ± 2.8 KJ/mol, ΔS 26.1 ± 1.8 J/mol*K. The eutectic has a composition of 13 mol.% Gd2S3 (0.74 GdF3 + 0.26 GdSF), the melting characteristics of the eutectic are 1182 ± 2°С, ΔН = 36.2 ± 2.5 KJ/mol, ΔS = 24.9 ± 1.7 J/mol*K. The phase diagram of the GdF3 - Gd2S3 system has been constructed. The balance equations for five phase transformations in the system, recorded by the DSC method, are compiled. Convergence was achieved in the construction of the liquidus of the system according to DSC data and the calculation according to the Redlich-Kister equation.

https://doi.org/10.1103/PhysRevB.107.125401

Here we present an analysis of the evolution of Majorana corner modes realizing in a two-dimensional higher-order topological superconductor (HOTSC) on a square lattice under the influence of local Coulomb repulsion. Both weak- and strong-interaction regimes are studied. It is shown that in the homogeneous system, the weak repulsion widens the region of the topologically nontrivial phase on the phase diagram. The open-boundary effect, resulting in spatial inhomogeneity of the system, leads to the appearance of the ground-state crossover as the repulsion intensity increases. Before the crossover, concentration correlators are $C_4$ symmetric and spin independent, and the corner states have energies that are determined by the overlap of the excitation wave functions localized at the different corners. After the crossover, the concentration correlators are spin dependent and possess the spontaneously broken symmetry. In turn, the corner excitation energy is size independent and defined by the Coulomb repulsion intensity with a quadratic law. In the strong-repulsion regime we derive the effective HOTSC Hamiltonian in the atomic representation and found a rich variety of interactions induced by virtual processes between the lower and upper Hubbard subbands. It is shown that Majorana corner modes still can be realized in the limit of the infinite repulsion, although the boundaries of the topologically nontrivial phase are strongly renormalized by Hubbard corrections.

https://doi.org/10.1016/j.intermet.2023.107871

Here we first report on the formation of epitaxial D0₃-Fe₃Rh(001) films grown during solid-state reaction in Rh/Fe(001) bilayers on MgO(001) substrates. Samples of the Fe₆₈Rh₃₂ composition above 400 °C showed the formation of a new ordered phase, in addition to the ordered B2–FeRh phase (space group Pm-3m, lattice constant a = 0.2993 nm), which becomes the dominant phase in Fe₇₆Rh₂₄ samples. These results and the results of the asymmetrical XRD φ-scan prove that the new ordered phase is the ordered D0₃-Fe₃Rh(001) phase (space group Fm-3m, lattice constant a = 0.5888 nm), forming a cube-on-cube orientation relationship with respect to the MgO(001) substrate. The D0₃-Fe₃Rh sample is a soft magnetic material with high saturation magnetization.

https://doi.org/10.3390/ijms24032144

Ca²⁺-triggered coelenterazine-binding protein (CBP) is a natural form of the luciferase substrate involved in the Renilla bioluminescence reaction. It is a stable complex of coelenterazine and apoprotein that, unlike coelenterazine, is soluble and stable in an aquatic environment and yields a significantly higher bioluminescent signal. This makes CBP a convenient substrate for luciferase-based in vitro assay. In search of a similar substrate form for the luciferase NanoLuc, a furimazine-apoCBP complex was prepared and verified against furimazine, coelenterazine, and CBP. Furimazine-apoCBP is relatively stable in solution and in a frozen or lyophilized state, but as distinct from CBP, its bioluminescence reaction with NanoLuc is independent of Ca²⁺. NanoLuc turned out to utilize all the four substrates under consideration. The pairs of CBP-NanoLuc and coelenterazine-NanoLuc generate bioluminescence with close efficiency. As for furimazine-apoCBP-NanoLuc pair, the efficiency with which it generates bioluminescence is almost twice lower than that of the furimazine-NanoLuc. The integral signal of the CBP-NanoLuc pair is only 22% lower than that of furimazine-NanoLuc. Thus, along with furimazine as the most effective NanoLuc substrate, CBP can also be recommended as a substrate for in vitro analytical application in view of its water solubility, stability, and Ca²⁺-triggering “character”.

 https://doi.org/10.3390/molecules28041569

Gd@C₈₂O_xH_y endohedral complexes for advanced biomedical applications (computer tomography, cancer treatment, etc.) were synthesized using high-frequency arc plasma discharge through a mixture of graphite and Gd₂O₃ oxide. The Gd@C₈₂ endohedral complex was isolated by high-efficiency liquid chromatography and consequently oxidized with the formation of a family of Gd endohedral fullerenols with gross formula Gd@C₈₂O₈(OH)₂₀. Fourier-transformed infrared (FTIR) spectroscopy was used to study the structure and spectroscopic properties of the complexes in combination with the DFTB3 electronic structure calculations and infrared spectra simulations. It was shown that the main IR spectral features are formed by a fullerenole C₈₂ cage that allows one to consider the force constants at the DFTB3 level of theory without consideration of gadolinium endohedral ions inside the carbon cage. Based on the comparison of experimental FTIR and theoretical DFTB3 IR spectra, it was found that oxidation of the C₈₂ cage causes the formation of Gd@C₈₂O₂₈H₂₀, with a breakdown of the integrity of the parent C₈₂ cage with the formation of pores between neighboring carbonyl and carboxyl groups. The Gd@C₈₂O₆(OOH)₂(OH)₁₈ endohedral complex with epoxy, carbonyl and carboxyl groups was considered the most reliable fullerenole structural model.

https://doi.org/10.1016/j.intermet.2023.107871

Here we first report on the formation of epitaxial D0₃-Fe₃Rh(001) films grown during solid-state reaction in Rh/Fe(001) bilayers on MgO(001) substrates. Samples of the Fe₆₈Rh₃₂ composition above 400 °C showed the formation of a new ordered phase, in addition to the ordered B2–FeRh phase (space group Pm-3m, lattice constant a = 0.2993 nm), which becomes the dominant phase in Fe₇₆Rh₂₄ samples. These results and the results of the asymmetrical XRD φ-scan prove that the new ordered phase is the ordered D0₃-Fe₃Rh(001) phase (space group Fm-3m, lattice constant a = 0.5888 nm), forming a cube-on-cube orientation relationship with respect to the MgO(001) substrate. The D0₃-Fe₃Rh sample is a soft magnetic material with high saturation magnetization.

https://doi.org/10.1039/D2CE01578A

https://doi.org/10.22184/1993-7296.fros.2022.16.2.116.125

 https://doi.org/10.1002/adom.202300076

Defects are a double-edged sword for heterovalent metal-ion doping phosphors. Along with the luminescence tunability of phosphors bestowed by defects, their expected luminescence efficiency would also be inevitably lowered due to the presence of these quenching sites. Herein, a chemical group substitution strategy is proposed, where inorganic polyhedrons act as the smallest chemical units during the structural evolution of the doping process. Such a method can not only effectively prevent the defect generation for charge compensation in heterovalent doping systems, but also facilitate the incorporation of activators into the matrix, leading to extremely high luminescence efficiency. The concept is first confirmed energetically favorable by first-principles simulations. As a robust experimental proof, two newly reported Mn⁴⁺-incorporated hexavalent organic-inorganic hybrid oxyfluorides (TMA)₂BO₂F₄:Mn⁴⁺ (where TMA stands for tetramethylammonium, and B = W⁶⁺ or Mo⁶⁺) present high quantum efficiency (up to 94.4%) and short lifetime (down to 2.26 ms) that are superior to the commercial red phosphor K₂SiF₆:Mn⁴⁺ (≈84.8%, ≈8.06 ms). Utilizing the differences in decay lifetimes and thermal quenching behaviors of (TMA)₂BO₂F₄:Mn⁴⁺ and K₂SiF₆:Mn⁴⁺, a time- and temperature-resolved single-color multiplexing mode with high-safety and easy-access is developed for information security. This work offers an effective strategy to manipulate defect generation in luminescent materials.

https://doi.org/10.1016/j.mtla.2023.101747

The solid-state reaction process in a multilayer thin film system (Al/Cu)₅₀ has experimentally been studied using the methods of simultaneous thermal analysis (STA) and in situ electron diffraction. A detailed kinetic analysis of the phase formation processes during the solid-state reaction has shown that the observed solid-state transformations can be described by a statistically significant kinetic model where each stage corresponds to the reaction of the n-th order with autocatalysis. The low-temperature stage has been demonstrated to be attributable to the formation of the θ-Al₂Cu phase, with the medium-temperature and high-temperature ones corresponding to the α₂-AlCu₃ and γ₁-Al₄Cu₉ phases, respectively. The kinetic parameters for the formation of the phases θ-Al₂Cu, α₂-AlCu₃ and γ₁-Al₄Cu₉ have been determined. It has been shown that the kinetic model describing the solid-state reaction in the Al–Cu multilayer thin film system is in best agreement with the experimental data in the case of a competition between the formation stages of the α₂-AlCu₃ and γ₁-Al₄Cu₉ phases.

https://doi.org/10.3390/polym15041005

The study addresses the growth of the wild-type strain Cupriavidus necator B-10646 and the synthesis of sulfur-containing polyhydroxyalkanoates (PHA) by this strain on media containing fructose and three different precursors (3-mercaptopropionic acid, 3′,3′-dithiodipropionic acid and 3′,3′-thiodipropionic acid). By varying the concentration and number of doses of the precursors added into the bacterial culture, it was possible to find conditions that ensure the formation of 3-mercaptopropionate (3MP) monomers from the precursors and their incorporation into the C-chain of poly(3-hydroxybutyrate). A series of P(3HB-co-3MP) copolymer samples with different content of 3MP monomers (from 2.04 to 39.0 mol.%) were synthesized and the physicochemical properties were studied. The effect of 3MP monomers is manifested in a certain decrease in the molecular weight of the samples and an increase in polydispersity. Temperature changes are manifested in the appearance of two peaks in the melting region with different intervals regardless of the 3MP content. The studied P(3HB-co-3MP) samples, regardless of the content of 3MP monomers, are characterized by equalization of the ratio of the amorphous and crystalline phases and have a close degree of crystallinity with a minimum of 42%, = and a maximum of 54%.

https://doi.org/10.1016/j.ssc.2023.115134

Sequence of structural transitions in the magnetically ordered region and a displacement-type structural transition at T = 220 K accompanied by the variation in the thermal expansion coefficient, ultrasound attenuation coefficient, g factor, and polarization current in the polycrystalline compound Ho_0.1Mn_0.9S was found. The electronic transitions above room temperature were established on the basis of the measurements of the conductivity, ultrasound attenuation maxima, and IR spectra.

 https://doi.org/10.3390/cryst13020362

New triple molybdates Li_xNa_1−xCaLa_0.5(MoO₄)₃:Er³⁺0.05/Yb³⁺0.45 (x = 0, 0.05, 0.1, 0.2, 0.3) were manufactured successfully using the microwave-assisted sol-gel-based technique (MAS). Their room-temperature crystal structures were determined in space group I4₁/a by Rietveld analysis. The compounds were found to have a scheelite-type structure. In Li-substituted samples, the sites of big cations were occupied by a mixture of (Li, Na, La, Er, Yb) ions, which provided a linear cell volume decrease with the Li content increase. The increased upconversion (UC) efficiency and Raman spectroscopic properties of the phosphors were discussed in detail. The mechanism of optimization of upconversion luminescence upon Li content variation was shown to be due to the control of excitation/energy transfer channel, while the control of luminescence channels played a minor role. The UC luminescence maximized at lithium content x = 0.05. The mechanism of UC optimization was shown to be due to the control of excitation/energy transfer channel, while the control of luminescence channels played a minor role. Over the whole spectral range, the Raman spectra of Li_xNa_1−xCaLa_0.5(MoO₄)₃ doped with Er³⁺ and Yb³⁺ ions were totally superimposed with the luminescence signal of Er³⁺ ions, and increasing the Li⁺ content resulted in the difference of Er³⁺ multiple intensity. The density functional theory calculations with the account for the structural disorder in the system of Li, Na, Ca, La, Er and Yb ions revealed the bandgap variation from 3.99 to 4.137 eV due to the changing of Li content. It was found that the direct electronic transition energy was close to the indirect one for all compounds. The determined chromaticity points (ICP) of the LiNaCaLa(MoO₄)₃:Er³⁺,Yb³⁺ phosphors were in good relation to the equal-energy point in the standard CIE (Commission Internationale de L’Eclairage) coordinates.

https://doi.org/10.1134/S1063774522070409

The structure of the labile co-crystal of 5-nitrimino-1,4Н-1,2,4-triazole with dimethyl sulfoxide was determined by X-ray diffraction. It was established that the molecule, previously known as 3(5)-nitramino-1,2,4-triazole, has a nitrimine structure. The geometric parameters of the molecules are similar to those of other nitrimino-1,2,4-triazoles. Intermolecular interactions in the co-crystal are considered. An explanation is provided for the lability of the co-crystal.

https://doi.org/10.1134/S1063776122120020

It has been shown that taking account of radiation from a material particle with negative relative permittivity ε_p that is in a dielectric medium with permittivity ε_m and experiences the action of an electromagnetic field prevents unlimited growth of particle’s electric dipole moment and its related electric fields if 2ε_m + ε_p → 0 and the medium and particle are lossless. Calculated radiation losses are embodied in a correction to the dielectric losses of a real particle. Using polystyrene with a silver nanoparticle showing negative permittivity in the optical range as an example, the behavior of the particle versus particle size has been studied for the permittivity varying in the interval –16 < ε_p < 16. It has been found that even if the permittivity of the nanoparticle is positive, taking the particle radiation into account considerably improves the accuracy of quasistatic calculation.

https://doi.org/10.1002/pssb.202200457

The content of transition-metal ions and their valence state for three compositions of Ni_xCu_yMn_3−x−yBO₅ are estimated by the methods of X-ray absorption spectroscopy. In all the three compositions, the copper content does not exceed 0.25. One of the compositions has manganese ions both in the trivalent and bivalent states according to the K-edge position. The calculations of the total energies of various cation-ordered structures using the software package Wien2K show that copper ions predominately occupy one site, namely, 2(2d). The measurements of the magnetic properties show two types of magnetic transitions in all the three compositions, with one of them being in the range of 60–75 K and the other one at 10 K. Based on the exchange interactions calculated in the framework of the empirical model, magnetic ordering temperatures are estimated for two- and three-sublattice structures and the magnetic transition in the range of 60–75 K is supposed to be connected with magnetic moment ordering in sites 2 and 3.

https://doi.org/10.1103/PhysRevA.107.023519

We studied Fresnel diffraction of a Laguerre-Gaussian beam ${\text{LG}}_{p,l}$ with arbitrary azimuthal $l$ and radial $p$ indices on a grating induced during its Raman interaction with a spatially periodic pump field in an atomic medium. The diffraction pattern turned out to be more complex than the classical Talbot effect observed when a plane wave illuminates a two-dimensional grating. The simulation results show that, under certain conditions, at distances corresponding to the classical Talbot planes (integer and fractional), periodic amplitude-phase distributions appear. The diffraction patterns are not a probe-field image in the induced grating plane, but a regular array of vortex annular-shaped microbeams with an inhomogeneous intensity distribution depending on the $l$ and $p$ indices and with a topological charge equal to that of the initial probe beam. The intensity and spatial distribution of diffraction patterns can be controlled by Raman amplification in the induced grating by varying the pump-field intensity or the Raman detuning.