Новые публикации

Anisotropic thermal expansion and electronic transitions in the Co3BO5 ludwigite

Kazak, N., Arauzo, A., Bartolomé, J., (...), Borus, A., Ovchinnikov, S. // Dalton Transactions//

 

The investigations of the crystal structure, magnetic and electronic properties of Co3BO5 at high temperatures were carried out using powder X-ray diffraction, magnetic susceptibility, electrical resistivity, and thermopower measurements. The orthorhombic symmetry (Sp.gr. Pbam) was observed at 300 K and no evidence of structural phase transitions was found up to 1000 K. The compound shows a strong anisotropy of the thermal expansion. A large negative thermal expansion along the a-axis is observed over a wide temperature range (T = 300-600 K) with αa = −35 M K−1 at T = 500 K with simultaneous expansion along the b- and c-axes with αb = 70 M K−1 and αc = 110 M K−1, respectively. The mechanisms of thermal expansion are explored by structural analysis. The activation energy of the conductivity decreases significantly above 700 K. Electronic transport was found to be a dominant conduction mechanism in the entire temperature range. The correlations between the thermal expansion, electrical resistivity, and effective magnetic moment were revealed and attributed to the evolution of the spin state of Co3+ ions towards the spin crossover and gradual charge-ordering transition.

Iron oxide nanoparticles synthesized by a glycine-modified coprecipitation method: Structure and magnetic properties

A.OmelyanchikabA.S.KamzincA.A.ValiullindV.G.SemenoveS.N.VereshchaginfM.VolochaevghA.DubrovskiygT.SviridovaiI.KozenkovaE.DolanbD.PeddisbjA.SokolovghV.Rodionovaa// Colloids and Surfaces A: Physicochemical and Engineering Aspects

https://doi.org/10.1016/j.colsurfa.2022.129090

Iron oxide magnetic nanoparticles (MNPs) are of interest in biomedicine and research owing to their moderate cytotoxicity and advanced properties, such as extensive surface-to-volume ratio and possibilities for tailoring their functionality through surface chemistry. To date, various approaches have been used for the synthesis of MNPs with controllable structural properties and various coatings to enhance their stability and functionality. This study describes a modified one-step method of coprecipitation in the presence of glycine allowing the production of particles with controllable size and in situ surface decoration. The effect of different glycine concentrations on the morphostructural and magnetic properties of iron oxide MNPs is studied. The particle size is reduced from 10.2 ± 0.3 to 7.2 ± 0.5 nm by increasing the glycine concentration from 0.06 up to 0.60 mol. The magnetic properties of obtained particles were tracked by SQUID magnetometry and Mössbauer spectroscopy. All samples of glycine capped iron oxide MNPs showed superparamagnetic behaviour at room temperature with maximal value of the saturation magnetization of 69 ± 4 Am2/kg. The results show the optimal concentration range of glycine which can be used in this method: a lower concertation than 0.15 mol does not affect the properties of obtained particles while higher concentrations than 0.3 mol lead to the reduction of magnetic properties (the saturation magnetisation reduces to 59 ± 3 Am2/kg when glycine concentration was 0.6 mol). The proposed economic and environment-friendly approach can be utilized to synthesise –NH2 functionalised MNPs for biomedical or wastewater treatment.

Stable Majorana Modes in Spin-Polarized Wire with Strong Interactions

Shustin, M. S.// Journal Of Superconductivity And Novel Magnetism//

For the 1D Hubbard model with spin-orbit coupling and proximity-induced s-wave superconductivity, the damping rates of quasiparticles are studied in the framework of density-matrix renormalization group (DMRG) approach. It is shown that low-energy excitations belonging to the Hubbard bands are stable against strong electron interaction at the spin-polarized regime. In order to confirm this result analytically, the low-energy model of the strongly interacting spin-polarized nanowire was derived in the second order of perturbation theory. This model generalizes Kitaev chain, taking into account the hoppings and anomalous pairings in the secondary coordination spheres as well as terms describing charge correlations. The amplitudes of the latter ones are small, and the system can be effectively described by quadratic Hamiltonian supporting stable Majorana excitations, which confirms numerical calculations. The topological phase diagram of effective model is studied in the framework of mean-field approximation. The evolution of topological phase boundaries under increasing of charge correlations is studied, and the important role of the joint realization of different types of interactions is noted. The results obtained can be applied when describing the Al-EuS-InAs hybrid system, recently synthesized and studied in searching for Majorana bound states.

Role of the surface effects and interparticle magnetic interactions in the temperature evolution of magnetic resonance spectra of ferrihydrite nanoparticle ensembles

Balaev, D. A.; Stolyar, S., V; Knyazev, Yu, V; Yaroslavtsev, R. N.; Pankrats, A., I; et al.// Results In Physics//

https://doi.org/10.1016/j.rinp.2022.105340

Ferrihydrite is characterized by the antiferromagnetic ordering and, in ferrihydrite nanoparticles, as in nanoparticles of any antiferromagnetic material, an uncompensated magnetic moment is formed. We report on the investigations of ferrihydrite powder systems with an average particle size of ∼ 2.5 nm obtained (i) as a product of the vital activity of bacteria (sample FH-bact) and (ii) by a chemical method (sample FH-chem). In the first approximation, these samples can be considered to be identical. However, in sample FH-chem, particles contact directly, while in sample FH-bact, they have organic shells; therefore, the interparticle magnetic interactions in these samples have different degrees. The main goal of this work has been to establish the effects of the interparticle magnetic interactions and individual characteristics of ferrihydrite nanoparticles on ferromagnetic resonance (FMR) spectra. The FMR spectra have been measured at different (9.4–75 GHz) frequencies in a wide temperature range. It has been found that, at low temperatures, the field-frequency dependence ν(HR) of the investigated systems has a gap ν/γ = HR + HA, where HR is the resonance field and HA is the induced anisotropy, which decreases with increasing temperature. To estimate a degree of the effect of interparticle interactions on the results obtained and to correctly determine the temperature range of the superparamagnetic (or blocked) state, the static magnetic measurement and Mössbauer spectroscopy data have been obtained and analyzed. It has been shown that the most striking feature of the FMR spectra - a gap in the field-frequency dependences - is a manifestation of individual characteristics of ferrihydrite nanoparticles. The induced anisotropy is caused by freezing of a subsystem of surface spins and its coupling with the particle core, which is observed in both samples at a temperature of ∼80 K. The temperature range (below 80 K) in which the gap exists corresponds to the blocked state in the FMR technique. In sample FH-bact, the ratio between the FMR parameters HA and linewidth ΔH obeys the standard expression HA ∼ (ΔH)3. In sample FH-chem, however, the interparticle magnetic interactions dramatically affect the behavior of parameters of the FMR spectra, which change nonmonotonically upon temperature variation. This fact is attributed to the collective freezing of the magnetic moments of particles under the conditions of sufficiently strong interactions, which follows from the temperature dependence of the particle magnetic moment relaxation time determined from the Mössbauer spectroscopy and static magnetometry data obtained in weak magnetic fields.

Preface

Ovchinnikov Sergei// Journal Of Superconductivity And Novel Magnetism//

https://doi.org/10.1007/s10948-022-06262-0

This Special Issue presents a selection of papers describing recent progress in the search for new materials with Tc approaching room temperature.

Magnetic Composite Coatings FeC and NiC Synthesized With Arabinogalactan

Stolyar, Sergey, V; Vazhenina, Irina G.; Yaroslavtsev, Roman N.; Chekanova, Lidia A.; Cheremiskina, Elena, V; et al.// Ieee Magnetics Letters//

DOI: 10.1109/LMAG.2022.3164631

In this work, we investigated the ferromagnetic resonance spectra of metal/carbon composite coatings. FeC and NiC coatings were synthesized by electroless deposition using polysaccharide arabinogalactan. An analysis of the angular dependences of the resonance field showed that the coatings consist of three magnetic phases separated by a nonmagnetic phase of carbon.

Spectrum of collective vibrations of vortex domain walls in a ferromagnetic nanostripe array

Orlov, Vitaly A.; Patrin, Gennady S.; Orlova, Irina N.// European Physical Journal B//

 https://doi.org/10.1140/epjb/s10051-022-00315-y

A problem of the spectrum of the collective periodic motion of vortex domain walls in a system of parallel ferromagnetic nanostripe is theoretically solved. The magnetic subsystems of stripes are coupled by the magnetostatic interaction. The effect of the distribution of vortex core polarities and chiralities on the character of periodic motion and the spectrum of collective modes of the nanostripe magnetization is discussed. Analytical expressions for the dispersion law and damping parameter of the collective periodic motion of vortex domain walls are obtained.

New double nonlinear-optical borate Rb3SmB6O12: Synthesis, structure and spectroscopic properties

Atuchin, Victor; Subanakov, Alexey; Aleksandrovsky, Aleksandr; Bazarov, Bair; Bazarova, Jibzema; et al. // Journal Of Alloys And Compounds//

https://doi.org/10.1016/j.jallcom.2022.164022

New noncentrosymmetric alkali rare-earth double borate Rb3SmB6O12 was found in the ternary system Rb2O–Sm2O3–B2O3. The Rb3SmB6O12 powder was prepared by the solid state reaction method at 750 °C for 40 h and the crystal structure was obtained by the Rietveld method. Rb3SmB6O12 crystallized in space group R32 with unit cell parameters a = 13.4874 (3) and c = 30.9398 (6) Å, V = 4874.2 (2) Å3, Z = 15. In the three-dimensional framework structure of Rb3SmB6O12, each [B5O10]5− group is linked to four different Sm-O polyhedra and, likewise, each Sm-O polyhedron is connected to four neighboring [B5O10]5− groups. The Sm-O polyhedra are formed by the face-sharing linked SmO6 octahedra. Rb+ cations are located in large cavities of the framework structure. From the thermal stability measurements, the incongruent melting of Rb3SmB6O12 is observed at 1104 K with as high melting enthalpy as Hm = –161.5 J/g. The nonlinear optical response of Rb3SmB6O12 tested via SHG is estimated to be similar to that of K3YB6O12. The Raman spectrum of Rb3SmB6O12 is mainly governed by the vibrations of BO4 and BO3 borate groups observed over the wavenumber range of 287–1550 cm–1. The spectral bands below 270 cm–1 were attributed to rotational, translational and mixed vibrations of Rb3SmB6O12 structural units. The luminescence spectrum of Sm3+ ions in the specific local environment of the Rb3SmB6O12 crystal lattice shows the ability to control the individual band intensity ratio originating from 4G5/2 level.

The spin-state transition in ACo(2)O(4) spinels (A = Be, Mg, Ca, Cd, Zn)

Zhandun, Vyacheslav S.; Draganyuk, Oksana N. // Journal Of Magnetism And Magnetic Materials//

https://doi.org/10.1016/j.jmmm.2022.169206

The magnetic and electronic properties of the Co-based spinel oxides ACo2O4 (A = Be, Mg, Ca, Zn, Cd) were studied within GGA + U approach. It was found that the Co3+ ion is in a low-spin state due to the effect of the crystal field of octahedral symmetry. It is shown that Co3+ ion undergoes a spin-state transition into the high-spin state under the critical pressure of P = −10 GPa – −20 GPa. This pressure-induced spin-state transition is caused by the redistribution of electrons between the t2g- and eg-orbitals arising with increasing interatomic distances. The role of interatomic distances between Co3+ ion and its ligands is discussed. Thin-film form also favors the appearance of a high-spin state of Co3+ ion. At the same critical pressure, there is a sharp increase in the majority spin bandgap and a sharp decrease in the minority spin bandgap. These findings allow manipulating the spin state of Co3+ ions and bandgap width through the pressure or strain arising in thin films.

CROSSOVER TEMPERATURE T-o FOR UNIAXIAL CALAMITIC NEMATIC MIXTURE

Aver'yanov, Evgeniy M. // Liquid Crystals And Their Application//

DOI: 10.18083/LCAppl.2022.1.67

The crossover temperature T-o corresponds to the minimum point at the dependence n(o)(T) of the ordinary refractive index for uniaxial liquid crystal. The temperature dependences of the extraordinary refractive index n(e)(T) and the birefringence Delta n(T) = n(e) - n(o) have no peculiarities at this point. For uniaxial nematic mesogen, the coefficients of the function Delta n(T) = Delta n(0)(1 - T/T-1)(beta) and the value Delta T-o = T-1 - T-o are of practical interest. The use of nematic mixtures makes it possible to vary these parameters in order to optimize operating characteristics of material. This work is devoted to determining the parameters Delta T-o and beta for calamitic nematic mixture consisting of different calamitic nematics of sort alpha with known parameters {p(alpha)} = {Delta T-o alpha, beta(alpha), B-1((alpha))}, where B-1((alpha)) = d n(T)(alpha)/dT, n (alpha) = (n(e) + 2n(o))(alpha)/3. The values Delta T-o and beta are shown to depend on the volume fractions phi(alpha) of the mixed components and parameters {p(alpha)}. The equation for determining Delta T-o was derived and its solutions were found for three binary nematic mixtures with different sets {p(alpha)}. Nonlinear dependences Delta T-o(phi(alpha)) and beta(phi(alpha)) for these mixtures were studied.

Enhanced sensitivity of an all-dielectric refractive index sensor with an optical bound state in the continuum

Maksimov, Dmitrii N.; Gerasimov, Valery S.; Bogdanov, Andrey A.; Polyutov, Sergey P. // Physical Review A//

https://doi.org/10.1103/PhysRevA.105.033518

The sensitivity of a refractive index sensor based on an optical bound state in the continuum is considered. Applying Zel'dovich perturbation theory we derived an analytic expression for bulk sensitivity of an all-dielectric sensor utili...

 

OPTICAL PROPERTIES OF MULTILAYER PHOTON STRUCTURES CONTAINING TWISTED NEMATIC COMPONENTS

Gunyakov, V. A.; Timofeev, I., V; Sutormin, V. S.; Krakhalev, M. N.; Parshin, A. M.; et al. // Liquid Crystals And Their Application//

https://doi.org/10.1016/j.optmat.2019.109630

Optical modes of a multilayered photonic structure with the twisted nematic liquid crystal as a defect layer have been investigated. The electroconvective flow in the nematic makes a spatially periodic structure in the form of abnormal rolls. Non-adiabatic propagation of polarized light in the defect layer causes unique features of the optical modes corresponding to the ordinary o-waves. The decay of these modes has been demonstrated with increasing voltage due to the effect of cross-polarization diffraction loss. The modes short-wave shift resulting from the contribution of the non-adiabatic geometric phase to the total phase delay of the wave during a round-trip propagation through the photonic structure has been found both experimentally and numerically.

ELECTRICALLY CONTROLLED IONIC MODIFICATION OF SURFACE ANCHORING IN LIQUID CRYSTAL MATERIALS

Sutormin, V. S.; Krakhalev, M. N.; Gardymova, A. P.; Prishchepa, O. O.; Timofeev, I., V; et al. // Liquid Crystals And Their Application//

A reorientation of cholesteric liquid crystal with a large helix pitch induced by the electrically controlled ionic modification of the surface anchoring has been studied. In initial state, the cholesteric helix is untwisted completely owing to the normal surface anchoring specified by the cations adsorbed at the substrates. As a result, the homeotropic director configuration is observed within the cell. Under the action of DC electric field, one of the substrates becomes free from the layer of surface active cations, therefore, setting the planar surface anchoring. The latter, in turn, leads to the formation of the hybrid chiral structure. The threshold value and dynamic parameters have been estimated for this process as well as the range of control voltages, which do not allow the electrohydrodynamic instabilities. The twisted hybrid director configuration observed in the experiment has been analysed by means of the simulation of polarisation change of light propagating through the cholesteric layer with asymmetric (planar and homeotropic) surface anchoring on the cell substrates.

STRUCTURE AND OPTICAL PROPERTIES OF SELF-ORGANIZED NEMATIC DOMAINS ENSEMBLES ON POLYCARBONATE SURFACE

Parshin, Alexandr M.; Gunyakov, Vladimir A.; Zyryanov, Victor Ya; Shabanov, Vasiliy F. // Liquid Crystals And Their Application//

The propagation of light through a hybrid-aligned nematic layer with a surface disclination line is investigated in a pulsed magnetic field. The experimental dependences of light intensity 𝐼I on time 𝑡t accompanied by interference oscillations are presented. The shift and expansion of the interference extrema as functions of the magnetic field pulse length during the reaction are shown. The 𝐼(𝑡)I(t) dependence for the relaxation process is calculated with allowance for scattering. The calculated 𝐼(𝑡)I(t) dependence agrees well with the experimental dependence over the entire hybrid-aligned nematic layer, except for the surface layer.

Machine Learning Analysis and Discovery of Zero-Dimensional ns(2) Metal Halides toward Enhanced Photoluminescence Quantum Yield

Maxim S. Molokeev*, Binbin Su, Aleksandr S. Aleksandrovsky, Nicolay N. Golovnev, Mikhail E. Plyaskin, and Zhiguo Xia*// CHEMISTRY OF MATERIALS//

https://doi.org/10.1021/acs.chemmater.1c02725

The dependence of photoluminescence quantum yield (PLQY) on the crystal structure of existing zero-dimensional ns2 metal halides is analyzed with the help of principal component analysis and random forest methods. The primary role of the distance between metal ions in different compounds is revealed, and the influence of other structural features such as metal-halogen distance and the distortion of metal-halogen polyhedrons are quantified. Accordingly, the two previously unknown Sb3+-based zero-dimensional metal halides were synthesized to verify the obtained model. Experimental studies of the two compounds demonstrated good agreement with the predictions, and the PLQY of (C10H16N)2SbCl5 is found to be 96.5%. Via machine learning analysis, we demonstrate that concentration quenching is the main factor that determines PLQY for all s2 ion metal halides, which will accelerate the discovery of new luminescence metal halides.

Structure and Properties of Exotic Nano- and Mesodiamonds with Pentagonal Symmetry

F. N. Tomilin, V. A. Pomogaev, Yu. A. Melchakova, P. V. Artyushenko, A. A. Shubin, A. M. Volodin, I. L. Zilberberg & P. V. Avramov // RUSSIAN PHYSICS JOURNAL//

https://doi.org/10.1007/s11182-022-02553-0

A comprehensive critical survey of structures of exotic nano-, meso- and microdiamonds with dodecahedral and icosahedral symmetry (N/MDPS) is presented. Due to their high dodecahedral or icosahedral symmetry, the unique complex atomic and electronic structure of N/MDPS leads to transport and mechanical properties very promising for photonic, quantum, and nanomechanical applications. To explain the nature of diamonds, theoretical models have been proposed based on the formation of twinned structures consisting of either 5 or 20 symmetrically equivalent tetrahedral and prismatic fragments of the face-centered cubic lattice with the formation of star-shaped or icosahedral clusters, respectively. It has been shown that these twinned nano- and mesodiamonds have limited dimensions due to accumulation of uncompensated structural stresses arising from the deviation of the angles between diamond <111> facets from perfect 72° in tetrahedral fragments of the face-centered cubic lattice to 70.5° between five symmetrically equivalent twinned fragments.

Polymer-Dispersed Cholesteric Liquid Crystal under Homeotropic Anchoring: Electrically Induced Structures with lambda(1/2)-Disclination

Anna P. Gardymova, Mikhail N. Krakhalev, Vladimir Yu. Rudyak, Vadim A. Barbashov, and Victor Ya. Zyryanov// POLYMERS //

https://doi.org/10.3390/polym14071454

Orientational structures of polymer-dispersed cholesteric liquid crystal under homeotropic anchoring and their transformations under the action of an electric field are studied. The switching of cholesteric droplets between different topological states are experimentally and theoretically demonstrated. Structures with λ+1/2-disclination are found and considered. These structures are formed during the transformation of a twisted toroidal configuration induced by a decrease in the electric field when a relative chiral parameter N0>6.3. The transformation of the initial structure with a bipolar distribution of the helix axis into a twisted toroidal configuration and then into a structure with λ+1/2-disclination is investigated in detail. The behavior of these structures under the influence of an external electric field, as well as the appearance of structures with λ1/2-disclination, are studied. Obtained results are promising for the development of optical materials with programmable properties.

Band Structure of Organic-Ion-Intercalated (EMIM)(x)FeSe Superconductor

Begunovich, Lyudmila V.; Korshunov, Maxim M. // Materials//

 https://doi.org/10.3390/ma15051856

The band structure and the Fermi surface of the recently discovered superconductor (EMIM)xFeSe are studied within the density functional theory in the generalized gradient approximation. We show that the bands near the Fermi level are formed primarily by Fe-d orbitals. Although there is no direct contribution of EMIM orbitals to the near-Fermi level states, the presence of organic cations leads to a shift of the chemical potential. It results in the appearance of small electron pockets in the quasi-two-dimensional Fermi surface of (EMIM)xFeSe.

Bound state in the continuum in an anisotropic photonic crystal supported by a full-wave phase plate

Pankin, Pavel S.; Maksimov, Dmitrii N.; Timofeev, Ivan, V // Journal Of The Optical Society Of America B-optical Physics//

We consider bound states in the continuum (BICs) in a 1D multilayered system of an anisotropic defect layer embedded into an anisotropic photonic crystal. We analytically demonstrate that an anisotropic defect layer embedded into anisotropic photonic crystal supports accidental BICs. These BICs can be transformed to high-Q resonances by variation of one of the system’s parameters. At the same time, the BICs are remarkably robust in the sense that a true BIC can be recovered by further tuning any of the system’s other parameters, leading to tunability of the resonance position.

Investigation of Spectral Properties of Chloroplast Grana System by Effective Medium Theory

Bikbaev, R. G.; Timofeev, I. V.; Shabanov, V. F. // Doklady Physics//

https://doi.org/10.1134/S1028335822020033

In this paper, the spectral properties of the triangular lattice of grana are investigated. By the finite difference time domain method, the transmittance spectra of the structure are calculated and the components of the scattering matrix are determined, which makes it possible to determine the effective parameters of the structure. As a result, it was shown that a two-dimensional lattice of grana can be represented as a homogeneous film with a thickness equal to the height of the grana. It is shown that the positions of the resonances before and after the homogenization of the structure coincide, which makes this method attractive for estimated calculations of the structure.

Synthesis and characterization of nanoscale composite particles formed by 2D layers of Cu-Fe sulfide and Mg-based hydroxide

Mikhlin, Yuri L.; Borisov, Roman V.; Vorobyev, Sergey A.; Tomashevich, Yevgeny V.; Romanchenko, Alexander S.; et al. // Journal Of Materials Chemistry A//

DOI: https://doi.org/10.1039/D2TA00877G

We introduce here a multifunctional material composed of alternating atomic sulfide sheets close to the composition of CuFeS2 and Mg-based hydroxide ones (valleriite), which are assembled due to their electric charges of opposite sign. Valleriite particles 50–200 nm in lateral size and 10–20 nm in thickness were synthesized via a simple hydrothermal pathway using various concentrations of precursors and dopants, and examined with XRD, TEM, EDS, X-ray photoelectron spectroscopy, reflection electron energy loss spectroscopy (REELS), Mössbauer, Raman and UV-vis-NIR spectroscopies, and magnetization, dynamic light scattering, and zeta potential measurements. The electronic, magnetic and optical characteristics are found to be critically dependent on the charge (electron density) at the narrow-gap sulfide layers containing Cu+ and Fe3+ cations, and can be tuned via the composition of the hydroxide part. Particularly, substitution of Mg2+ with Al3+ increases the negative charge of the hydroxide layers and reduces the content of Fe3+-OH centers (10–45% of total iron); the effects of Cr and Co dopants entering both layers are more complicated. Mössbauer doublets of paramagnetic Fe3+ detected at room temperature transform into several Zeeman sextets at 4.2 K; the hyperfine fields up to 500 kOe and complex magnetic behavior, but not pure paramagnetism or antiferromagnetism, were observed for valleriites with the higher positive charge of the sulfide sheets, probably due to the depopulation of the minority-spin 3d states of S-bonded Fe3+ ions. Aqueous colloids of valleriite show optical absorption at 500–750 nm, which, along with the peaks at the same energies in REELS, may arise due to quasi-static dielectric resonance involving the vacant Fe 3d band and being dependent on the composition of both layers too. These and other findings call attention to valleriites as a new rich family of 2D materials for a variety of potential applications.

ALD Stripline Resonator and Bandpass Filters for VHF and UHF Bands

Belyaev, Boris; Serzhantov, Alexey; Balva, Yaroslav; Galeev, Rinat; Lemberg, Konstantin; et al. // 2021 Ieee Mtt-s International Microwave Filter Workshop (Imfw)//

DOI: 10.1109/IMFW49589.2021.9642365

It is shown that for an optimal substrate thickness ALD technology will be promising for IF bandpass filter designing. A two-conductor stripline ALD resonator with central frequency 200 MHz will have Q-factor 53 with total length 3.7 mm (0.0025λ g ) and the frequency separation of the first and the second oscillation modes up to 59. Two bandpass filters for VHF and UHF designed and fabricated for commercial application display good agreement between the simulation and the experiment. A 3-pole bandpass filter with central frequency 255 MHz and lateral size 15.8×3.2 mm 2 has stopband width 13.5f 0 , and a 6-pole bandpass filter with central frequency 1250 MHz and lateral size 4.4×5.1 mm 2 has stopband width 9.4f 0 .

Microstructural Parameters for Modelling of Superconducting Foams

Koblischka, Michael Rudolf; Koblischka-Veneva, Anjela; Nouailhetas, Quentin; Hajiri, Ghazi; Berger, Kevin; et al. // Materials//

 https://doi.org/10.3390/ma15062303

Superconducting YBa2Cu3Oy (YBCO) foams were prepared using commercial open-cell, polyurethane foams as starting material to form ceramic Y2BaCuO5 foams which are then converted into superconducting YBCO by using the infiltration growth process. For modelling the superconducting and mechanical properties of the foam samples, a Kelvin-type cell may be employed as a first approach as reported in the literature for pure polyurethane foams. The results of a first modelling attempt in this direction are presented concerning an estimation of the possible trapped fields (TFs) and are compared to experimental results at 77 K. This simple modelling revealed already useful information concerning the best suited foam structure to realize large TF values, but it also became obvious that for various other parameters like magnetostriction, mechanical strength, percolative current flow and the details of the TF distribution, a refined model of a superconducting foam sample incorporating the real sample structure must be considered. Thus, a proper description of the specific microstructure of the superconducting YBCO foams is required. To obtain a set of reliable data, YBCO foam samples were investigated using optical microscopy, scanning electron microscopy and electron backscatter diffraction (EBSD). A variety of parameters including the size and shape of the cells and windows, the length and shape of the foam struts or ligaments and the respective intersection angles were determined to better describe the real foam structure. The investigation of the foam microstructures revealed not only the differences to the original polymer foams used as base material, but also provided further insights to the infiltration growth process via the large amount of internal surface in a foam sample.

Dielectric Model of Thawed and Frozen Organic Soil at the AMSR Radiometer Frequency

Mironov, V. L.; Kosolapova, L. G.; Savin, I., V // Izvestiya Atmospheric And Oceanic Physics//

In this paper, we develop a simple single-frequency dielectric model of thawed and frozen arctic soil for a frequency of 6.9 GHz. The model is developed based on laboratory dielectric measurements of soil samples containing 80–90% organic matter in the range of gravimetric moisture from 0.01 to 0.942 g/g (volumetric moisture ranging from 0.007 to 0.573 cm3/cm3), and temperatures from +25 to –30°C in the freeze mode. A refractive mixture model is used as a regression equation for the measured values of the complex soil refractive index depending on moisture. The complex refractive indices of various soil components (mineral-organic , bound, transitional, and free water (ice for frozen soil)), as well as values for the maximum allowable content of bound and transitional water in the soil at all measured temperatures, are determined using the regression analysis. The empirical dependences of the complex refractive index of soil components and the maximal allowable contents of various types of water in soil on temperature are obtained. As a result, we developed a model that allows calculating the permittivity of thawed and frozen organic soil as a function of moisture and temperature at 6.9 GHz. The root-mean-square error was 0.20 for the real part of the complex dielectric permittivity of the soil and 0.22 for the imaginary part at the determination coefficient values of 0.999 and 0.995, respectively.

SI: Advances in Density Functional Theory (DFT) Studies of Solids

Oreshonkov, Aleksandr S. // Materials//

 https://doi.org/10.3390/ma15062099

This summary is a review on articles published in the Special Issue “Advances in Density Functional Theory (DFT) Studies of Solids” from the section “Materials Simulation and Design” of the MDPI journal Materials. Nowadays, the DFT method is widely used to calculate structural, electronic, optical, vibrational, etc., properties of materials. There is no doubt that analysis of new and practically important compounds should be carried out within the framework of theoretical (computational) and experimental methods combination. The well-established computational codes [1,2,3] based on the DFT approach were used in papers published in this Special Issue. The 7 articles discussed below [4,5,6,7,8,9,10], written by 37 authors, are excellent examples of DFT application to study various properties of solids.

Role of the surface effects and interparticle magnetic interactions in the temperature evolution of magnetic resonance spectra of ferrihydrite nanoparticle ensembles

Balaev, D. A.; Stolyar, S., V; Knyazev, Yu, V; Yaroslavtsev, R. N.; Pankrats, A., I; et al. // Results In Physics//

https://doi.org/10.1016/j.rinp.2022.105340

Ferrihydrite is characterized by the antiferromagnetic ordering and, in ferrihydrite nanoparticles, as in nanoparticles of any antiferromagnetic material, an uncompensated magnetic moment is formed. We report on the investigations of ferrihydrite powder systems with an average particle size of ∼ 2.5 nm obtained (i) as a product of the vital activity of bacteria (sample FH-bact) and (ii) by a chemical method (sample FH-chem). In the first approximation, these samples can be considered to be identical. However, in sample FH-chem, particles contact directly, while in sample FH-bact, they have organic shells; therefore, the interparticle magnetic interactions in these samples have different degrees. The main goal of this work has been to establish the effects of the interparticle magnetic interactions and individual characteristics of ferrihydrite nanoparticles on ferromagnetic resonance (FMR) spectra. The FMR spectra have been measured at different (9.4–75 GHz) frequencies in a wide temperature range. It has been found that, at low temperatures, the field-frequency dependence ν(HR) of the investigated systems has a gap ν/γ = HR + HA, where HR is the resonance field and HA is the induced anisotropy, which decreases with increasing temperature. To estimate a degree of the effect of interparticle interactions on the results obtained and to correctly determine the temperature range of the superparamagnetic (or blocked) state, the static magnetic measurement and Mössbauer spectroscopy data have been obtained and analyzed. It has been shown that the most striking feature of the FMR spectra - a gap in the field-frequency dependences - is a manifestation of individual characteristics of ferrihydrite nanoparticles. The induced anisotropy is caused by freezing of a subsystem of surface spins and its coupling with the particle core, which is observed in both samples at a temperature of ∼80 K. The temperature range (below 80 K) in which the gap exists corresponds to the blocked state in the FMR technique. In sample FH-bact, the ratio between the FMR parameters HA and linewidth ΔH obeys the standard expression HA ∼ (ΔH)3. In sample FH-chem, however, the interparticle magnetic interactions dramatically affect the behavior of parameters of the FMR spectra, which change nonmonotonically upon temperature variation. This fact is attributed to the collective freezing of the magnetic moments of particles under the conditions of sufficiently strong interactions, which follows from the temperature dependence of the particle magnetic moment relaxation time determined from the Mössbauer spectroscopy and static magnetometry data obtained in weak magnetic fields.

Quantum versus classical nature of the low-temperature magnetic phase transition in TbAl3(BO3)(4)

Zajarniuk, T.; Szewczyk, A.; Gutowska, M. U.; Puzniak, R.; Szymczak, H.; et al. // Physical Review B//

DOI: https://dx.doi.org/10.1103/PhysRevB.105.094418

Specific heat CB of a TbAl3(BO3)4 crystal was studied for 50 mK <T< 300 K with emphasis on T<1 K where a phase transition was found at Tc=0.68 K. Nuclear, nonphonon (Cm), and lattice contributions to CB were separated. Lowering of Tc with an increase in magnetic field parallel to the easy magnetization axis (B) was found. It was established that Cm and a Grüneisen ratio depend on B and T in a way characteristic of systems in which a classical transition is driven by quantum fluctuations (QFs) to a quantum critical point at T=0 by tuning a control parameter (B). The BT phase diagram was constructed, and the dynamical critical exponent 0.82z0.96 was assessed. Nature of the transition was not established explicitly. Magnetization studies point at the ferromagnetic ordering of Tb3+ magnetic moments, however, lowering of Tc with increase in B is opposite to the classical behavior. Hence, a dominant role of QFs was supposed.

XMCD and ab initio study of interface-engineered ultrathin Ru/Co/W/Ru films with perpendicular magnetic anisotropy and strong Dzyaloshinskii-Moriya interaction

Samardak, Alexander S.; Ognev, Alexey, V; Kolesnikov, Alexander G.; Stebliy, Maksim E.; Samardak, Vadim Yu; et al. // Physical Chemistry Chemical Physics//

DOI: https://doi.org/10.1039/D1CP05456B

Understanding the nature of recently discovered spin–orbital induced phenomena and a definition of a general approach for “ferromagnet/heavy-metal” layered systems to enhance and manipulate spin–orbit coupling, spin–orbit torque, and the Dzyaloshinskii–Moriya interaction (DMI) assisted by atomic-scale interface engineering are essential for developing spintronics and spin-orbitronics. Here, we exploit X-ray magnetic circular dichroism (XMCD) spectroscopy at the L2,3-edges of 5d and 4d non-magnetic heavy metals (W and Ru, respectively) in ultrathin Ru/Co/W/Ru films to determine their induced magnetic moments due to the proximity to the ferromagnetic layer of Co. The deduced orbital and spin magnetic moments agree well with the theoretically predicted values, highlighting the drastic effect of constituting layers on the system's magnetic properties and the strong interfacial DMI in Ru/Co/W/Ru films. As a result, we demonstrate the ability to simultaneously control the strength of magnetic anisotropy and intermixing-enhanced DMI through the interface engineered inversion asymmetry in thin-film chiral ferromagnets, which are a potential host for stable magnetic skyrmions.

Phase transitions and p-T phase diagram of the multiferroic TbFe3(BO3)(4) crystal

Alexander Krylov, Maksim Pavlovskiy, Yuri Kitaev, Irina Gudim, Nikita Andryshin, Aleksander Vtyurin, Qinghui Jiang, Svetlana Krylova// Journal Of Raman Spectroscopy//

https://doi.org/10.1002/jrs.6341

The structural phase transitions in multiferroic TbFe3(BO3)4 with change hydrostatic pressures and temperatures have been studied by Raman spectroscopy and calculation within density functional theory. Lattice dynamics calculations in the TbFe3(BO3)4 crystal in the 𝑅32R32 phase under various values of applied hydrostatic pressure (from 0 up to 5 GPa with 1 GPa step) were performed. The calculation performed in this work in a TbFe3(BO3)4 crystal showed that the applied pressure can increase the phase transition temperature. Raman spectra of the TbFe3(BO3)4 crystal have been investigated at simultaneously high temperature and high pressure (up to 5.14 GPa and 465 K). The appearance of a soft mode was observed with decreasing temperature at normal pressure. The manifestations of the interaction of the structural and magnetic order parameters in the range from 13 to 50 K were observed at normal pressure. With increasing pressure and a fixed temperature, recovery of the soft modes is also observed. The experimental p–T phase diagram of TbFe3(BO3)4 was established. An increase in pressure leads to an increase in the temperature of transition.

Synthesis, Crystal Structure and Thermodynamic Properties of Apatite-like Lead Gadolinium Vanadato-germanates

Denisova, Lyubov T.; Molokeev, Maksim S.; Golubeva, Evgenia O.; Galiakhmetova, Nadezhda A. // Journal Of Siberian Federal University-chemistry//

 DOI:10.17516/1998-2836-0277

The Pb10-xGdx(GeO4)2+x(VO4)4-x (x = 0.5, 1.0) apatites were synthesized by the solid-phase synthesis by roasting stoichiometric mixtures of PbO, Gd2O3, GeO2, and V2O5 in air at temperatures of 773–1073 K. Their crystal structure was determined using X-ray diffraction analysis. The high-temperature heat capacity (350–1000 K) was measured by differential scanning calorimetry. The experimental data Cp = f (T) were used to calculate the thermodynamic properties of apatites.

 

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