Новые публикации

One- and two-particle correlation functions in the cluster perturbation theory for cuprates

Kuz'min, V. I.; Nikolaev, S. V.; Korshunov, M. M.; Ovchinnikov, S. G.// arXiv.org, e-Print Archive, Condensed Matter (2023)//


Physics of high-Tc superconducting cuprates is obscured by the effect of strong electronic correlations. One way to overcome the problem is to seek for an exact solution at least within the small cluster and expand it to the whole crystal. Such an approach is in the heart of the cluster perturbation theory (CPT). Here we develop CPT for the dynamic spin and charge susceptibilities (spin-CPT and charge-CPT), within which the correlation effects are explicitly taken into account by the exact diagonalization. We apply spin-CPT and charge-CPT to the effective two-band Hubbard model for the cuprates obtained from the three-band Emery model and calculate one- and two-particle correlation functions, namely, spectral function and spin and charge susceptibilities. Doping dependence of the spin susceptibility was studied within spin-CPT and CPT-RPA that is the CPT generalization of the random phase approximation (RPA). Both methods produce the low energy response at four incommensurate wave vectors in qualitative agreement to the results of the inelastic neutron scattering on overdoped cuprates.

On Estimating the Critical Current Density in Polycrystalline Superconductors Synthesized by Solid-State Method

Gokhfeld, D.M.// Journal of Superconductivity and Novel Magnetism//


In a recent paper, Zhang et al. [1] studied the effect of a Pb content on the superconducting properties of Bi-2223. Some earlier, Ramírez et al. [2] explored the effect of compaction pressure on the Bi-2212. In both studies, the critical current densities were estimated and compared for a series of polycrystalline superconducting samples. The synthesis conditions for the highest critical current density were claimed in both works. This comment explains that the average granule size should be used instead of the sample size in the Bean formula for the polycrystalline superconductors synthesized by solid-state, sol–gel, electrospinning, and solution blow spinning methods. The corrected estimations for the commented articles conclude that the synthesis conditions affect both the granule size and the intragranular critical current density. The synthesis parameters for the highest critical current density conditions are clarified.

Correlation Between Magnetic and Electric Properties in the Series of CoxZnl1 – xFe2O4 Nanoparticles

D. Petrov, I. Edelman, A. Thakur, P. Thakur, A. Sukhachev & S. Ovchinnikov// JETP Letters//


Magnetization dependences of CoxZnl1 – xFe2O4 nanoparticles (x = 0, 0.1, 0.2, 0.3, 0.4, 0.5) synthesized with the citrate precursor technique on an external magnetic field and temperature are presented. Ferrimagnetic order in nanoparticles with x ≥ 0.2 appeared at temperatures, T, exceeding room temperature, and in nanoparticles with x = 0 and 0.1 at T near 100 K. The saturation magnetization, Ms, remnant magnetization, Mr, and the coercive force, Hc, increase with x increase and the temperature decrease. Ms reached very high value: Ms of NPs with x = 0.5 equals to 106.6 emu/g at 100 K while, according to the literature data, Ms of stoichiometric bulk Co ferrite equals to 90 emu/g at 4.2 K. Correlations between concentration dependences of magnetic and electric properties has been revealed and explained qualitatively.

Clustering into Three Groups on a Quantum Processor of Five Spins S = 1, Controlled by Pulses of Resonant RF Fields

Pichkovskiy, I.S., Zobov, V.E.// Applied Magnetic Resonance//


We consider a quantum processor based on five qutrits represented by spins S = 1, which is driven by radio frequency (RF) pulses selective in transitions between adjacent levels. Numerical simulation of the implementation of the quantum-adiabatic clustering algorithm was performed on the example of partitioning a set of six points into three groups. We find the amplitudes and durations of rectangular RF pulses, as well as the durations of free evolution intervals in the control pulse sequence, which made it possible to engineer a time-dependent effective Hamiltonian in the discrete-time approximation. Also we studied the dependence of the implementation fidelity on the parameters. We took quadrupole nuclei as qutrits, but the results obtained will be useful for controlling quantum processors based on qutrits represented by other systems.

Bound States in the Continuum Protected by Reduced Symmetry of Three-Dimensional Open Acoustic Resonators

Bin Jia, Lujun Huang, Artem S. Pilipchuk, Sibo Huang, Chen Shen, Almas F. Sadreev, Yong Li, and Andrey E. Miroshnichenko// Physical Review Applied//


Bound states in the continuum (BICs) have been demonstrated as a powerful tool for trapping acoustic fields in an acoustic resonator. It has been widely recognized that symmetry-protected (SP) BICs result from symmetry incompatibility of some eigenmodes of a resonator with propagating modes of waveguides. The most typical example of SP BIC is the odd eigenmode of the resonator with the eigenfrequency embedded into the propagating band of even propagating eigenmodes of the waveguide. In this work, we consider a more sophisticated case of an acoustic cuboid resonator that is opened by the attachment of two cylindrical waveguides. We show that BICs can be sustained in an open acoustic resonator with reduced symmetry. For symmetrical positions of waveguides, the eigenmodes of the cuboid can also be classified as SP BICs and show different stability against the shifts of waveguides from the positions of symmetry of the cuboid. We fabricate a series of coupled waveguide resonators and experimentally verify the existence of these BICs by identifying the vanished linewidth of Fano resonance in transmission spectra. Besides, we also show that evanescent modes of waveguides play a role in the formation of BICs in a nonaxisymmetric waveguide-resonator system by tuning the angle θ between two waveguides. Consequently, the eigenmodes remain SP BICs for θ = 0° and θ = 180° but convert into accidental BICs at θ ≈ 85°or θ ≈ 275°. Such accidental BICs are also experimentally verified. Our results enrich the understanding of SP BICs and accidental BICs, and provide alternative methods of routing acoustic waves and designing acoustic devices requiring fine spectrum features, such as filters and sensors.

Higher-order magnetic skyrmions in nonuniform magnetic fields

M. S. Shustin, V. A. Stepanenko, and D. M. Dzebisashvili// Phys. Rev. B//


For a two-dimensional Hubbard model with spin-orbit Rashba coupling in external magnetic field the structure of effective spin interactions is studied in the regime of strong electron correlations and at half-filling. It is shown that in the third order of perturbation theory, the scalar and vector chiral spin-spin interactions of the same order arise. The emergence of the latter is due to orbital effects of magnetic field. It is shown that for nonuniform fields, scalar chiral interaction can lead to stabilization of axially symmetric skyrmion states with arbitrary topological charges. Taking into account the hierarchy of effective spin interactions, an analytical theory on the optimal sizes of such states, the higher-order magnetic skyrmions, is developed for axially symmetric magnetic fields of the form h(r)rβ with βR.


Growth Conditions and the Structural and Magnetic Properties of Cu2MBO5 (M = Cr, Fe, Mn

E. M. Moshkina, N. A. Belskaya, M. S. Molokeev, A. F. Bovina, K. A. Shabanova, D. Kokh, Yu. V. Seretkin, D. A. Velikanov, E. V. Eremin, A. S. Krylov & L. N. Bezmaternykh // Journal of Experimental and Theoretical Physics//


Copper oxyborate single crystals with a ludwigite structure, Cu2MBO5 (M = Cr, Fe, Mn), containing different substitutes in the trivalent subsystem have been grown from Bi2O3–MoO3–Na2O–B2O3 fluxes. The structural properties of grown compounds have been compared in detail using X-ray diffraction and Raman spectroscopy methods. In addition, these methods have been used to determine the degree of cationic ordering in these ludwigites. The temperature and field dependences of the Cu2MBO5 (M = Cr, Fe, Mn) ludwigite magnetization are presented.

Combined Porous-Monolithic TiNi Materials Surface-Modified with Electron Beam for New-Generation

Journal of Functional Biomaterials//


TiNi alloys are very widely used materials in implant fabrication. When applied in rib replacement, they are required to be manufactured as combined porous-monolithic structures, ideally with a thin, porous part well-adhered to its monolithic substrate. Additionally, good biocompatibility, high corrosion resistance and mechanical durability are also highly demanded. So far, all these parameters have not been achieved in one material, which is why an active search in the field is still underway. In the present study, we prepared new porous-monolithic TiNi materials by sintering a TiNi powder (0–100 µm) on monolithic TiNi plates, followed by surface modification with a high-current pulsed electron beam. The obtained materials were evaluated by a set of surface and phase analysis methods, after which their corrosion resistance and biocompatibility (hemolysis, cytotoxicity, and cell viability) were evaluated. Finally, cell growth tests were conducted. In comparison with flat TiNi monoliths, the newly developed materials were found to have better corrosion resistance, also demonstrating good biocompatibility and potential for cell growth on their surface. Thus, the newly developed porous-on-monolith TiNi materials with different surface porosity and morphology showed promise as potential new-generation implants for use in rib endoprostheses.

Rudner Photonic Topological Insulators in the Language of the Zhegalkin Operators

Fedchenko, D., Kulikov, V., Timofeev, I.// Nonlinear Phenomena in Complex Systems//


A topological insulator is a material that exhibits the properties of a conductor on the surface and of an insulator in the bulk. The Rudner game is a simplified model of a topological insulator implemented on a two-dimensional photonic lattice of resonators, which is described in the language of tricolor four-cycle two-dimensional Wolfram cellular automata. It is a case of a regular two-dimensional lattice, in which each cell is colored in one of three colors (for a photonic topological insulator, these colors mean the presence of a photon in a resonator, the absence of a photon, and a topological insulator boundary). By setting the transformation rule for each cell, depending on the state of the nearest neighbors and the cell itself, for equal discrete time intervals we obtain a cellular automaton. In this study, the Rudner game is rewritten equivalently in terms of operators in the Zhegalkin polynomial ring with coefficients in a field consisting of three elements.

Magneto-Optical Spectroscopy of Nanocomposites (CoFeZr) x (Al2O3) 1 0 0 - x

Gan'shina, E.A., Granovsky, A.B., Garshin, V.V., (...), Ryl'kov, V.V., Nikolaev, S.N.// SPIN//


We present results of magneto-optical investigations of (CoFeZr)x(Al2O3)100x3)100−� film nanocomposites in transverse Kerr effect (TKE) geometry in the spectral range 0.5–4.0eV and magnetic field up to 3.0kOe. Nanocomposites were deposited onto a glass-ceramic substrate by ion-beam sputtering. The TKE response at room temperature strongly depends on the wavelength of light, applied magnetic field H and the volume metallic fraction. From the analysis of the field dependences of TKE at different wavelengths, it follows that in the as-deposited samples, the interaction between nanoparticles at x<30�<30at.% is small and the nanocomposite is an ensemble of superparamagnetic particles; as x increases to 32at.%, a superspinglass-type state arises, then, in the vicinity of 34at.%, along with individual superparamagnetic particles, superferromagnetic regions appear. Long-range ferromagnetic order arises at concentrations x less than the percolation threshold for conductivity xper=42.6�per=42.6at.%. In the presence of two different magnetic states in the samples, TKE is not proportional to the magnetization. Both the field dependences at near-infrared region and the spectral dependences of TKE change significantly after annealing of the samples, while the changes in the field dependences of the magnetization are almost imperceptibly.

Majorana vortex modes in spin-singlet chiral superconductors with noncollinear spin ordering: Local density of states study

Zlotnikov, A.O.// Physical Review B//


In this study, topologically nontrivial edge and vortex bound states are described in the coexistence phase of chiral spin-singlet superconductivity and noncollinear spin ordering on a triangular lattice in the presence of few (up to four) vortices. We consider the topological phase transition induced by the magnetic order between the phase hosting Majorana modes and the initial phase of the chiral d-wave superconductivity supporting non-Majorana modes which is also topologically nontrivial. The change of the excitation spectrum at the critical point is obtained in both cases of open and periodic boundary conditions in the presence of vortices. It is proved that zero-energy Majorana modes localized at vortex cores are caused by noncollinear long-range magnetic ordering. Even though nearby excitation energies of subgap states including the edge-localized and vortex-localized states are very close to each other, the energy difference between different vortex bound states is an order of magnitude higher. This difference determines the energy gap for Majorana vortex modes separating them from other vortex bound states. It is found that even in the presence of noncollinear spin ordering its value can be estimated from the excitation energy of vortex bound states in the pure chiral d-wave state for the nonmagnetic case. By studying local density of states near the vortex cores the possibility to experimentally detect the described Majorana vortex modes by scanning tunneling microscopy is discussed. It is demonstrated that Majorana vortex modes and Majorana antivortex modes induced by noncollinear magnetism have different features in energy and spatially resolved density of states due to the chiral symmetry on the superconducting order parameter.

Short Note on the Observation of Ambient Condition Room Temperature Superconductivity in Nitrogen-Doped Lutetium Hydride

Awana, V.P.S., Felner, I., Ovchinnikov, S., Robinson, J.W.A.// Journal of Superconductivity and Novel Magnetism//


The field of superconductivity has attracted eight Nobel prizes so far—five for experimental discoveries and three for theoretical advance. Since the discovery of superconductivity, the quest for materials which show superconductivity at ambient conditions has been a major priority. The observation of superconductivity at room temperature (RT) in N-doped lutetium hydride [1] has therefore attracted much excitement, but also a number of open questions; for example, a recent comment [2] notes the limitations of the experimental techniques used in [1] to confirm superconductivity at RT—these are mostly limited to measurements of zero electrical resistivity using a standard four-probe electrical technique. However, ultimate proof of superconductivity requires the observation of a non-decaying (i.e., persistent) supercurrent in a ring geometry as executed by Kamerlingh Onnes in 1914 [3]. Furthermore, an ideal superconductor will show infinite electrical conductivity as well as perfect diamagnetism [4]. In view of the limited verification methods in [1] and points raised in [2,3,4] and elsewhere, this short note highlights reports of RT superconductivity in the literature that spectacularly backfired.

Phases, Microstructure and Magnetic Properties in a Severely Deformed Cr-Ni–Al Alloy

D.E., Noskov, F.M., Komogortsev, S.V., Volochaev, M.N.// Journal of Superconductivity and Novel Magnetism//


The phases, microstructure, and magnetic properties in a severely deformed Cr-Ni–Al alloy have been studied. The eutectic microstructure observed in localized regions of the alloy can be interpreted as a result from the super-Arrhenius relaxation of the alloy. According to X-ray diffraction and magnetometry, the nanosized nickel inclusions in the matrix of the chromium-nickel γ-solid solution are formed. It is shown that, after severe (superplastic) deformation, a unidirectional magnetic anisotropy is induced, which may be associated with the antiferromagnetic coupling between the CrNi2 matrix and the nickel inclusions.

Structural and magnetic transitions in the Bi2Fe4O9/BiFeO3 composite

Udod, L.V., Aplesnin, S.S., Sitnikov, M.N., (...), Romanova, O.B., Kharkov, A.M.// Journal of Alloys and Compounds//


A Bi2Fe4O9/BiFeO3 composite with a percentage ratio of 67/33 has been synthesized, its morphological analysis has been carried out. The average crystallite sizes for each phase have been determined. The magnetization hysteresis has been established and the temperature of its disappearance has been found. Using the infrared absorption spectra, temperatures of the magnetic phase transitions in each phase have been determined from the magnetic susceptibility, magnetostriction constant, ultrasound damping coefficient, and phonon mode softening. The change of magnetostriction constant sign observed in the vicinity of the spin reorientation transition and antiferromagnetic transition in mullite has been attributed to the change of the sign of the magnetoelastic constants. The interaction between the phases in the composite and the correlation of its structural and magnetic properties have been established.

Flux growth and phase diversity of the triple oxides of transition metals (Mn,Fe,Ga)2O3 in multicomponent fluxes based on Bi2O3-MoO3-B2O3-Na2O

Moshkina, E., Seryotkin, Y., Bayukov, O., (...), Krylov, A., Bezmaternykh, L.// CrystEngComm//

DOI https://doi.org/10.1039/D3CE00147D

To determine the mutual influence of the solvent and soluble in multicomponent fluxes based on Bi2O3–MoO3–B2O3–Na2O, the crystallization of the triple oxides of the transition metals (Mn,Fe,Ga)2O3 is investigated, namely the phases based on orthorhombic FeGaO3 and bixbyite FeMnO3. Simultaneously, a set of fluxes is studied based on the variation in the component ratio with regard to the solvent and soluble. The crucial role of various components of the flux system is considered at the intersection of the phase boundaries. Fluxes for the stable growth of (Mn,Fe,Ga)2O3 single crystals of the studied phases (based on orthorhombic FeGaO3 and bixbyite FeMnO3) are determined. A set of single crystal samples (9 samples) with different Fe/Mn/Ga ratios is obtained. The actual composition of the samples is studied using the EDX technique. The partition coefficients of Fe2O3, Mn2O3 and Ga2O3 in the studied fluxes are analyzed. The structure of the obtained samples is characterized using X-ray diffraction methods, including the phase composition, space group and lattice parameters. The room temperature Raman spectra of the obtained samples are presented. The distribution of iron cations over the crystal positions in the obtained phases is studied using Mössbauer spectroscopy.

Optical coupled-mode theory for dielectric solids of revolution

Bulgakov, E.N., Maksimov, D.N., Ershov, A.E.// Physical Review A//


We propose a single resonance coupled-mode approach to light scattering by dielectric solids of revolution. By using a biorthogonal decomposition of the S matrix found with the extended boundary condition method we derived all parameters required for application of the temporal coupled-mode theory in a closed form. The proposed approach allows for constructing a frequency-dependent Fano response due to a single resonance after the full-wave solution has been found at a single incident frequency.

Magnetic Nanoscalpel for the Effective Treatment of Ascites Tumors

Zamay, T., Zamay, S., Luzan, N., (...), Svetlichnyi, V., Kichkailo, A.// Journal of Functional Biomaterials//


One of the promising novel methods for radical tumor resection at a single-cell level is magneto-mechanical microsurgery (MMM) with magnetic nano- or microdisks modified with cancer-recognizing molecules. A low-frequency alternating magnetic field (AMF) remotely drives and controls the procedure. Here, we present characterization and application of magnetic nanodisks (MNDs) as a surgical instrument (“smart nanoscalpel”) at a single-cell level. MNDs with a quasi-dipole three-layer structure (Au/Ni/Au) and DNA aptamer AS42 (AS42-MNDs) on the surface converted magnetic moment into mechanical and destroyed tumor cells. The effectiveness of MMM was analyzed on Ehrlich ascites carcinoma (EAC) cells in vitro and in vivo using sine and square-shaped AMF with frequencies from 1 to 50 Hz with 0.1 to 1 duty-cycle parameters. MMM with the “Nanoscalpel” in a sine-shaped 20 Hz AMF, a rectangular-shaped 10 Hz AMF, and a 0.5 duty cycle was the most effective. A sine-shaped field caused apoptosis, whereas a rectangular-shaped field caused necrosis. Four sessions of MMM with AS42-MNDs significantly reduced the number of cells in the tumor. In contrast, ascites tumors continued to grow in groups of mice and mice treated with MNDs with nonspecific oligonucleotide NO-MND. Thus, applying a “smart nanoscalpel” is practical for the microsurgery of malignant neoplasms.

Surface barrier of holes drilled in a type-II superconductor

By: Gokhfeld, D. M.// arXiv.org, e-Print Archive, Condensed Matte//


Holes drilled in a type-II superconductor trap the magnetic flux. Following Clem's flux pinning model, we consider surface pinning as a mechanism for compressing the magnetic flux in the holes. Estimations of the trapped magnetic flux demonstrate that the holes with the diameter up to 2 mm are advantageous for bulk single-crystal REBCO samples. The REBCO films and tapes can be improved by the holes with diameter smaller than 10 μm.

Manifestation of Majorana modes overlap in the Aharonov-Bohm effect

By: Aksenov, S. V.// Journal of Physics: Condensed Matte//

DOI 10.1088/1361-648X/ac62a7

One of the key features of the Majorana bound states emerging in topological superconducting (SC) wires is increasing oscillations of their energy under the growth of magnetic field or chemical potential due to concomitant enhancement of hybridization of the Majorana mode wave functions initially localized at the opposite edges of the structure. In this study we found that the other consequence of it is a shift of Aharonov–Bohm (AB) oscillations of linear-response conductance in an interference device where two ends of the SC wire connected with a normal contact via non-SC wires (arms). In addition, it is accompanied by an oscillation period doubling. The numerical calculations for the spinful system are supported by the analytical results for different spinless models allowing to track the conductance evolution as the hybridization of the Majorana modes increases. It is shown that since the coupling between the different arms and normal contact is implemented only via the different-type Majoranas the AB oscillations acquire a fundamental π/2 shift in comparison with the effect for an analogous system of zero-energy quantum dots.

Structure and Vibrational Spectroscopy of C-82 Fullerenol Valent Isomers: An Experimental and Theoretical Joint Study

by Felix N. Tomilin, Polina V. Artyushenko, Irina A. Shchugoreva, Anastasia V. Rogova, Natalia G. Vnukova, Grigory N. Churilov, Nikolay P. Shestakov, Olga N. Tchaikovskaya, Sergei G. Ovchinnikov, and Pavel V. Avramov// Molecules//


Gd@C82OxHy 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.

Near-Field Evolution of Optical Vortices and Their Spatial Ordering behind a Fork-Shaped Grating

Ikonnikov, D.A., Myslivets, S.A., Arkhipkin, V.G., Vyunishev, A.M.// Photonics//


Fork-shaped gratings are periodic structures containing a spatial dislocation known to be used for the production of optical vortices in a far field. Spatial overlapping of diffraction orders in a near field results in complex spatial evolution of optical vortices. In this paper, we report the results of near-field diffraction on fork-shaped gratings with different topological charges and analyze the evolution of specific optical vortices during propagation. Optical vortices have been shown to form two-dimensional well-ordered spatial configurations in specific transverse planes. The locus of points of optical singularities has been shown to form two helical lines twisted around the ±1±1 diffraction order directions. Our results demonstrate that the spatial behaviour of optical vortices is in close connection with the spatial ordering arising from the Talbot effect. The quantity of optical vortices demonstrates complex spatial dynamics, which includes spatial oscillations and decreasing along the propagation direction. These results provide a foundation towards a deeper understanding of near-field singular optics phenomena.

Structural characteristics of radiation-amorphized ZrSiO4:U,Th according to Raman spectroscopy of Boson peak

Shchapova, Y.V., Krylov, A.S., Votyakov, S.L.// Journal of Raman Spectroscopy//


The structure of the amorphous fraction and the tensile-compressive stresses in amorphous-crystalline radiation-damaged zircon ZrSiO:U,Th depending on radiation dose and temperature (8–350 K) are investigated according to Raman spectroscopy of Boson peak for the first time. The Boson peak at 60–70 cm−1 associated with localized phonon states in the amorphous fraction (��) is recorded at low temperatures (�<100 K) for samples with ��<30% and over the entire temperature range 8–350 K for ��>70%. The wider localized states distribution in the latter case is considered as a sign of the amorphous phase structure evolution with an increase in radiation dose. The estimates of an atomic correlation radius based on the Ioffe–Regel criterion are similar to those in glasses, ◂,▸ nm. The monotonic increase in �� value during heating of zircon with ��>70% is governed by thermal expansion of the percolating amorphous fraction. The nonmonotonic variations of the �� value in zircon with ��<30% is determined by the stresses in the amorphous fraction due to the mismatch in thermal expansion coefficient (CTE) and elastic moduli of the amorphous and crystalline phases depending on temperature; a change in the sign of the crystalline fraction CTE at 30 K is assumed. The Boson peak disappearance at 100 K in zircon with ��<30% during heating conforms to with the violation of the phonon localization as a consequence of amorphous fraction contraction and partial ordering. The data obtained are important for predicting the thermal and mechanical properties of heterogeneous radiation-damaged materials and nanocomposites.

Adsorption of Organic Dyes by Fe3O4@C, Fe3O4@C@C, and Fe3O4@SiO2 Magnetic Nanoparticles

Ivanova, O.S., Edelman, I.S., Sokolov, A.E., (...), Lin, C.R., Chen, Y.Z.// Bulletin of the Russian Academy of Sciences: Physics//


Fe3O4@C, Fe3O4@C@C, and Fe3O4@SiO2 core–shell nanoparticles are synthesized via thermal decomposition and coprecipitation. Samples are characterized via X-ray spectroscopy, transmission electron microscopy, and magnetometry. It is shown that the magnetic core of all nanoparticles is nanocrystalline and has crystal parameters corresponding to only one phase of Fe3O4, covered with a uniform shell of amorphous carbon or silicon oxide around 8 nm thick. Special attention is given to adsorption properties of the nanoparticles with respect to four dyes: Methylene blue, Congo Red, Eosin Y, and Rhodamine C. The high selectivity of Fe3O4@C nanoparticles to various dyes is revealed.

Nearly flat bands and ferromagnetism in the terminated Mn2C MXene

Kozak, V.V., Fedorova, N.A., Olshevskaya, J.S., (...), Tomilin, F.N., Avramov, P.V.// Computational Condensed Matter//


Using Density Functional Theory and Periodic Boundary Conditions it is shown that the hydroxylated/oxygenated/halogenated Mn2C monolayer is a 2D ferromagnetic material with a local Mn ions magnetic moment of 2.7μв per unit cell. Upon oxygenation the ferromagnetic coupling between Mn ions can be transformed into a superposition of magnetic states. In particular, the intrinsic magnetic moments in the hydroxylated/halogenated Mn2C monolayer can attain up to 6μB per unit cell. It is found that oxygen termination induces flat bands in the band structure, which evidence for the strong electron correlations and could lead to the implementation of exotic quantum phases in 2D crystals and high-temperature superconductivity. Along with the potential of the hydroxylated Mn2C monolayer characterized by the half-metallicity for application in spintronic devices as a perfect spin injector/detector, this material like other conventional MXenes is promising for the use in energy storage, electromagnetic interference shielding, and sensing.

Interparticle magnetic interactions and magnetic field dependence of superparamagnetic blocking temperature in ferrihydrite nanoparticle powder systems

Krasikov, A.A., Knyazev, Y.V., Balaev, D.A., (...), Yaroslavtsev, R.N., Iskhakov, R.S.// Physica B: Condensed Matter//


In this study, nanoparticles of initial synthetic ferrihydrite have been coated with arabinogalactan. The synthesized series of samples with different degrees of coverage of particles has been characterized by X-ray photoelectron spectroscopy, Mössbauer spectroscopytransmission electron microscopy and magnetometry. The superparamagnetic blocking temperature decreases monotonically with an increase in the degree of coverage of ferrihydrite particles, which is unambiguously related to the different role of the interparticle magnetic interactions in the investigated powder systems. Analysis of the field dependence of the blocking temperature within the random anisotropy model has shown that an increase in the degree of coverage of ferrihydrite particles leads to a decrease in the size of a cluster in which the behaviors of the nanoparticle magnetic moments are correlated. The results obtained have shown the possibility of effective control of the strength of magnetic interparticle interactions in powder ferrihydrite systems by coating nanoparticles with arabinogalactan.

Validation of Dobson's, Schmugge's, and Mironov's Dielectric Models at Four Typical Agrosoils of Krasnoyarsk and Krasnodar krais

Fomin, S., Muzalevskiy, K., Karavayskiy, A., (...), Alexey, L., Mikhailets, M.// IEEE//

DOI: 10.1109/RMC55984.2022.10079332

In this article, in a wide frequency range from 300 MHz to 2 GHz at a temperature of 20C, the validation of Dobson's, Schmugge's, and Mironov's (with one, two, and three soil water relaxations) dielectric models was carried out using four samples of typical agrosoils taken from the arable layer. Variations in the clay fraction, dry bulk density, and organic matter content of soil samples ranged from 32% to 56%, from 1.1 g/cm 3 to 1.7 g/cm 3 , up to 6.9%, respectively. It is shown that the Mironov's model with two relaxations (M2) has the best accuracy in describing the measured relative complex permittivity (RCP) spectra for all soils in average. The coefficient of determination (R 2 ) and root-mean square error (RMSE) appeared to be equal of R2ε=0.907 (RMSEε=0.83) for real and R2ε=0.960(RMSEε=0.89) for imaginary parts of RCP, when comparing the measured and calculated RCPs. Error of soil moisture retrieval, based on M2 dielectric model and the observations of reflection coefficient at nadir was estimated. For four agricultural soils, it is shown that the retrieved volumetric soil moisture values with the determination coefficient R2=0.975 and RMSE =2% coincide with the true values of soil moisture. It has also been found that small inaccuracies (several tens of percent) in determining the dry bulk density and clay content of soils have practically no effect on the error in retrieving the volumetric soil moisture.

Numerical-Analytical Model of Reflection Coefficient for Rough Soil Surface in Wide Frequency Range

Muzalevskiy, K.// Proceedings - 2022 IEEE 8th All-Russian Microwave Conference

DOI: 10.1109/RMC55984.2022.10079255

In this work, a numerical-analytical model of reflection coefficient for rough soil surface in wide frequency band was proposed. The field of reflected wave from the rough soil surface is presented as the sum of secondary fields from an infinite set of elementary horizontal scattering plates (with a given average size). The field from each elementary scattering plate is represented as an average field from the result of stochastic interference of an infinite set of coherent elementary sources of secondary waves. The vertical position of the elementary sources is determined by the stochastic height of the soil surface within elementary plate. The case of the coherent component and the total value (coherent+diffuse components) of reflection coefficient is considered. On the basis of the created model of reflection coefficient, a broadband method for simultaneously retrieved the root-mean-square deviation of the stochastic soil surface heights and volumetric soil moisture was developed. The results have a wide application value both for single-frequency and multi-frequency radar and radiometric methods of soil moisture measuring.

Temperature phase transitions in silver niobate and lithium tantalate-modified silver niobate ceramics

Krylov, A.S., Krylova, S.N., Vtyurin, A.N., (...), Tian, Y., Wei, X.// Physical Chemistry Chemical Physics.//


The temperature behaviour of 0.955 AgNbO3–0.045 LiTaO3 and AgNbO3 ceramics was studied in the range from 10 to 415 K using Raman spectroscopy. Ab initio calculations of the Raman spectra in the Pmc21 phase of AgNbO3 were carried out using three potentials (A-PZ, PBE, and PBEsol) for spectral interpretation. The peculiarities in the Raman spectra in AgNbO3 ceramics are observed and explained. The differences in the spectra of the 0.955 AgNbO3–0.045 LiTaO3 and AgNbO3 ceramics are shown. The temperatures of the structural changes in the 0.955 AgNbO3–0.45 LiTaO3 and AgNbO3 ceramics were discussed. A structural phase transition below 120 K was observed in silver niobate. A phase transition was observed at 310 K and below 150 K in 0.955 AgNbO3–0.045 LiTaO3.

Temperature and vibration OTDR measurements with a single mode-multimode-single mode fiber structure

Aleksandr Yu. Igumenov, Igor V. Melnikov, Arsenii A Afanasiev, Sandaara S. Popova, Sergey N. Lukinykh, Igor A. Tambasov, Alexei S. Lagutchev// Progress in Biomedical Optics and Imaging - Proceedings of SPIE, 12372, art. no. 123720P//


We suggest a prototype of a fiber-optic sensor system that is based on a simple singlemode-multimode-singlemode fiber structure and serial OTDR. The sensor has simple structure, made of affordable components, exploits easy measuring principle, immunes to EMI or RFI, and has confident response to measure key environment variables at a very long span. From the experimental results, the relationship between the temperature of water and output signal of the temperature sensor can be determined. After some maths, we can determine the temperature of the water by measuring the optical power loss of the at the SMS structure in a temperature range of 30 to 70 °C. This SMS structure is shown to carry out vibration measurement for 0.1-60 Hz frequencies with high accuracy. The OTDR exploited allows carrying out far-field measurements when SMS structure is spliced in long fiber-optic link.


Karavayskiy, A.Yu., Lukin, Yu.I., Pogoreltsev, E.I.// Earth's Cryosphere//

Earth's Cryosphere, 27(1), pp. 23-34. 2023. 

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