Issue 1, 2025

Magnetic phase transitions in FeRh-based alloys

A. S. Komlev$^1$

The study of the mechanisms of first-order magnetic phase transitions is one of the urgent problems of modern physics. The complexity of determining these mechanisms is associated with the multitude of factors that play a significant role in the phase transition. FeRh-based alloys are among the most typical objects in which a first-order phase transition from the antiferromagnetic to the ferromagnetic state is observed. Despite the fact that the iron-rhodium alloy has a fairly simple crystal structure and does not change the symmetry of the crystal lattice during the phase transition, a number of features in the behavior of its physical properties are observed. The presented review describes current information on the influence of various external factors, the influence of crystal defects and dimensional features on the static and dynamic properties of FeRh-based alloys.

N. S. Blokhina

The paper presents an overview of the works on the study of the natural phenomenon of the thermal bar (thermobar). The results of field observations of this phenomenon in lakes in spring and autumn are presented, giving an idea of the thermo-hydrodynamic processes in water bodies during these periods. In works on laboratory modeling of the thermal bar, the instability mechanisms leading to its occurrence and features of its movement are discussed. Theoretical works are considered, where various approaches to modeling the thermal bar are discussed, including modern hydrodynamic models. Special attention is paid to works on studying this phenomenon at the Department of Physics of the Sea and Land Waters of the Physics Faculty of the Moscow State University.

Investigation of magnetic and magneto-optical properties of copper cobalt ferrite nanoparticles

M. Moradi$^1$, A. RAFIEE

In this study, copper cobalt ferrite nanoparticles were synthesized by chemical formula Co1-xCuxFe2O4 and (x = 0, 0.2, 0.4, 0.6, 0.8, 1) by co-precipitation method. The X-ray diffraction pattern of the samples confirmed the single-phase spinel structure of the fabricated nanoparticles and the average size of the crystals was calculated from the entire width of the diffraction peak with the highest intensity and Scherrer’s equation. Using transmission electron microscope images, the nanoparticle size was about 10 nm. The magnetic properties of copper cobalt ferrite nanoparticles were measured by Alternative Gradient Force Magnetometer )AGFM( and it was seen that with increasing substitution of copper Cations instead of cobalt Cations in the samples, the amount of induction decreased and the saturation magnetization first increased and then decreased. In order to investigate the Faraday’s effect on copper cobalt ferrite nanoparticles, the transmittance values were measured using a laboratory experiment and their graphs were plotted in terms of the applied magnetic field, all of which were in agreement with the theory. In addition, transmittance was investigated for two angular positions of the analyzer at -45˚ and +45˚ in different fields.

Elliptically Dependent Inclusion of The Initial Momentum in The Barrier Suppression Ionization Rate

M. Kurtović$^1$, V. M. Petrović$^2$, I. D. Petrović$^3$

We theoretically studied and observed the photoionization rates of the alkali and noble atoms driven by an elliptically polarized Ti:Sapphire laser, for the barrier suppression ionization scheme. We extended the barrier suppression ionization formula developed by Posthumus and co-workers, by considering the inclusion of the initial momentum of the ejected photoelectrons and the ponderomotive potential and Stark shift in unperturbated ionization potential. Extended formula is applied on both groups of atoms and obtained results are compared with these obtained by the initial formula with the aim to determine the influence of all mentioned effects. Additionally, we explored influence of the field’s ellipticity on the barrier suppression ionization rate. We found that it is sensitive to the change of the field ellipticity, and inclusion of all mentioned effects as well.

D. A. Chernousov, D. P. Agapov

The paper discusses the possibilities of deep learning in solving the inverse problem of computational ghost polarimetry. For the first time it is shown that the spatial distribution of the polarization properties of objects with linear amplitude anisotropy is restored using a neural network trained on model data. The spatial distribution of the parameters of linear amplitude anisotropy is determined with an accuracy of 7.8 and 15.6\% for azimuth of anisotropy and value of anisotropy, respectively.

Modeling the depth sensitivity of a Setup for Rapid Measurement of Carbon Concentrations in Soil

A. V. Andreev$^{1,2}$, N. A. Fedorov$^2$, T. Yu. Tretyakova$^{1,2,3}$, Yu. N. Kopach$^2$, D. N. Grozdanov$^{2,4}$, I. N. Ruskov$^4$

The tagged neutron method (TNM) is widely used for position sensitive elemental analysis of various substances and materials. One of the promising applications of this method is the rapid determination of carbon content in soil. The use of portable tagged neutron generators makes it possible to carry out field measurements without preliminary preparation of the samples under study. This article is devoted to the analysis of the possibility of using this method to measure depth profiles of carbon concentration in soil. A setup consisting of a tagged neutron generator ING-27 and 20 BGO-based $\gamma$-ray detectors was simulated using GEANT4 and the sensitivity of the method to different layers of carbon concentration was determined.

K. A. Bornikov$^1$, I. P. Volobuev$^2$, Yu. V. Popov$^{2,3}$

The process of Compton collapse of positronium by a twisted photon in the A^2 approximation is considered. In the case of a Bessel cylindrical wave, the matrix element of such a process is closely related to a similar matrix element for a plane electromagnetic wave. Taking into account the law of conservation of momentum and within the framework of the standard scattering theory, it is shown that in terms of the probability of this process, almost all the most important characteristics of the cylindrical wave of a twisted photon are lost. Moreover, it is shown that the differential probability of positronium collapse by a twisted photon is equal to the probability of collapse by a photon with a certain momentum moving at a certain angle to the z axis averaged over the azimuthal angle of the incoming photon.

Theoretical reconstruction of emitting gas parameters during the flare SOL2015-10-01

V. A. Maliytin$^1$, Yu. A. Kupryakov$^2$, K. V. Bychkov$^3$, A. B. Gorshkov$^4$, O. M. Belova$^5$

The solar flare SOL2015-10-01 was observed by us at the Astronomical Institute of the Czech Academy of Sciences on HSFA-2 – a horizontal setup for solar research. After processing the spectra, the integral radiation fluxes in the H$\alpha$, H$\beta$, H$\varepsilon$ hydrogen lines, D3 helium line, violet $\lambda=3968$ \AA{} and infrared $\lambda=8542$ \AA{} calcium lines were determined. The flare in question had two characteristic cores and the fluxes from each of them were determined during processing. Within the framework of the heated gas model, a theoretical calculation of the plasma parameters was performed taking into account the physical conditions in the chromosphere, including self-absorption in the spectral lines. Comparison of six lines at once allowed us to restore the temperature, density and spatial structure of the radiating gas with a high degree of confidence. The gas is found out to be inhomogeneous via temperature. The reconstructed values of gas concentration exceed typical prominence values by more than an order of magnitude. One should consider the chromospheric origin of the emitting gas.

Specialized Rectangular Mask Pattern Design to Neutralize Charging Effects

P. Zhang$^1$

In order to achieve a high-quality transfer of the mask pattern onto the substrate in plasma etching, it is important to minimize charging effects. This study investigates the potential use of a specialized design for rectangular mask holes to counteract charging effects. The research examines the behavior of a single and deformed rectangular mask hole with varying length-to-width ratios and two types of mask arrays. A particle simulation program was utilized to analyze the changes in electric field distribution and simulated opening during etching time. The findings indicate that ions tend to bombard the long side rather than the short side or vertexes, leading to flattening of deformed sides and resulting in an approximately rectangular etched opening. Specialized designs based on specific arrays can aid in achieving nearly perfect rectangular etched openings, with potential underlying mechanisms extensively discussed in this study. These results offer valuable insights into specialized design strategies for plasma etching processes.

A. K. Kurnosov$^{1,2}$, A. N. Kropotkin$^1$, A. A. Chukalovsky$^1$, A. T. Rakhimov$^1$, T. V. Rakhimova$^1$, G. G. Balint-Kurti$^3$, A. P. Palov$^1$

The v→v rate coefficients for the vibrationally inelastic collisions of O atoms with O$_2$ molecules are presented for vibrational quantum numbers v from 0 to 8 and temperatures from 100K to 1000K. State-to-state rate coefficients were computed theoretically using an ab initio O-O$_2$ interaction potential for the ground state of O$_3$ and the final rate coefficients are obtained by summing the state-to-state rate constants over final rotational states and averaging over an equilibrium Boltzmann distribution of relative translational energies and initial rotational states at temperatures of interest in plasma processes. The rate constants obtained are compared with available quasi-classical calculations. The coefficients obtained are required in the modeling of many industrial processes such as plasma etching, surface treatment, plasma sterilization, and medicine.

I. A. Bogatyrev$^1$, M. B. Vavilov$^1$, I. A. Sukharev$^2$, E. T. Shavgulidze$^2$

In the paper, a model of the motion of a Brownian particle on $\mathbb{C}^2$ is studied. A six-dimensional random process, the states of which are described by the coordinates of the particle and a complex analogue of the area swept by the radius vector of a point as it moves along the trajectories of a four-dimensional Brownian bridge is considered. Using methods of integration over the conditional Wiener measure, it is possible to obtain an expression for the probability density of the transition of a random process from an arbitrary state to a subsequent one. A connection is revealed between the trajectories of the process under consideration and the Heisenberg group constructed over the field of complex numbers $H_3(\mathbb{C})$. The continuity in time and the H\"{o}lder property with order $\alpha<1/2$ of the oriented area function $S(t)$ are proved, as well as the Heisenberg Markov property of the process. The heat equation describing the evolution of the system and the corresponding sub-Laplacian are found. The solution to the equation is obtained in the form of a functional integral. The performance of a Wick rotation allows to draw an analogy between the process under consideration and the movement of an electron in a magnetic field.

G. A. Krasyukov$^{1,2}$, O. V. Pavlovsky$^{1,2}$

The localized fermionic states arising in an effective field theory model of graphene on the substrate generating a spatially inhomogeneous mass gap were studied. It was shown that in case of terraced-stepped structure of the substrate inhomogeneity in which the chiral mass has the opposite sign on different terraces, both massless and massive fermionic states are generated. The mass spectrum of such states depends on the size of the mass gap generated by the substrate, as well as the width of the terraces, the number of terraces in the substrate structure, and the width of the transition step.

P. N. Nikolaev

In this work, a phase diagram of the neighborhood of the critical point of a one-component system in the van der Waals approximation is constructed. It is shown that this approximation makes it possible to describe the critical point corresponding to the coexistence of three aggregate states of matter – solid, liquid and gaseous. The possibility of using this approximation for triple points of other types is discussed.

E. I. Nikulin, V. T. Volkov, D. A. Karmanov

For a singularly perturbed reaction-diffusion equation with periodic coefficients, the structure of the inner transition layer in the case of a balanced reaction with a weak discontinuity is investigated. The existence of periodic solutions with an internal transition layers is proved, the question of their stability is investigated, and asymptotic approximations of solutions of this type are obtained. It is shown that in the case of reaction balance, the presence of even a weak (asymptotically small) reaction gap can lead to the formation of several contrasting structures of finite size, both stable and unstable.

I. I. Tsiniaikin$^1$, A. S. Andreeva$^1$, P. O. Mikhailov$^1$, M. A. Kolpakov$^1$, G. V. Nibudin$^1$, A. S. Trifonov$^1$, G. V. Presnova$^2$, M. Yu. Rubtsova$^2$, D. E. Presnov$^1$, O. V. Snigirev$^1$, V. A. Krupenin$^1$

A control system for the laser interferometer for the reactive ion etching setup was developed. A series of chips with the same structure were fabricated for precise calibration of the upper silicon layer of the silicon-on-insulator material etching rate. The thickness of the structure on each chip varied depending on the etching time. The height of the resulting steps was measured using the semicontact mode of an atomic force microscope. For the etching regime in CF4 and O2 gas plasma (flow ratio 20:5, pressure 4 Pa, power 40 W), the silicon etching rate is 0.31 ±0.1 nm/s. The adduce parameters allow stopping silicon etching at a depth of ~ 5 to 120 nm with an accuracy of no worse than 2 nm. The obtained results make allow to solve a number of problems in creating various nanoelectronic devices. In particular, in silicon nanowires creation, processes of thermal oxidation and subsequent washing of the oxide of the unetched structure are used very often and leads to a significant improvement in the transistor channels characteristics.

M. S. Shilov$^1$, A. V. Nazarov$^{1,2}$, V. S. Chernysh$^1$, A. S. Shemukhin$^{1,2}$

The surface binding energy of atoms in solids is an important parameter for sputtering under ion beam irradiation. In case of multicomponent materials sputtering, such as alloys, the ratio of the alloy components’ surface binding energies determines the preferential sputtering process. In this paper the surface binding energy of atoms in the NixPdy alloys with various stoichiometry is calculated using molecular dynamics simulation. The surface binding energy dependency on the alloy components’ concentrations is shown. The surface binding energy temperature dependencies and the binding energy for the atoms of the second atomic layer are also calculated.

O. Yu. Yurakova$^{1,2,3}$, R. A. Baulin$^3$, M. A. Andreeva$^3$

The formula describing the scattering on a one-dimensional paracrystals (Hosemann R. // Zeitschrift für Physik. 128. 465. (1950)) is generalized for the case of X-ray scattering in grazing geometry (GISAXS – Grazing Incidence Small Angle X-ray Scattering) on a radial paracrystals, taking into account the refraction and attenuation of radiation by the reflecting and scattering medium. The formula is applicable to the description of GISAXS scattering maps on nanocomposite quasi-amorphous structures.

A. P. Zharkova$^1$, D. A. Tovmasian$^{1,2}$, A. P. Chernyaev$^1$, A. V. Nechesnyuk$^2$, S. M. Varzar$^1$, A. A. Loginova$^2$

The concept of constructing additional target margins has proven itself well in the field of photon radiation therapy. In this regard, it is a generally accepted method that provides the necessary dose distribution during planning. However due to the interaction characteristic of photon radiation with matter in the case of the strong tissue heterogeneity, the planning of radiation therapy requires an assessment of the plan robustness or the creation of the plan resistant to existing dose delivery errors. The study tested the robustness of radiation therapy plans using two irradiation technologies – CRT (conformal radiation therapy) and IMRT (intensity-modulated radiation therapy). In total, 15 plans of patients with metal prostheses were included in the analysis. The patient position relative to the isocenter of the irradiation beams was geometrically shifted, modeling possible setup errors of the patient. The information about the actual displacements of patients obtained during pretreatment visualization was analyzed – about 25 thousand treatment fractions with different tumor locations. According to the results of the study, the probability that the necessary dose distribution will not be provided for the clinical volume of the target is no more than 0.04 ± 0.03 % when using the CRT technique and no more than 7 ± 4 % when using IMRT. Thus, the CRT plans showed greater robustness with respect to the target in case of irradiation patients with high-density prostheses. If it is necessary to use IMRT techniques, it is required to pay increased attention to the patient’s setup and to check the plan for robustness.

V. V. Bagatinskaya$^{1,2,3}$, N. A. Diansky$^{1,2,3}$, V. A. Bagatinsky$^{1,2,3,4}$, A. V. Gusev$^{2,3,4}$, E. G. Morozov$^4$

The contributions of geostrophic and wind-driven factors to the formation of the mean climatic structure of the Antarctic circumpolar current (ACC) were studied using the INMOM (Institute of Numerical Mathematics Ocean Model) general ocean circulation model. The aim of the work was to study the structure of the ACC with a quantitative assessment of geostrophic and wind-driven contributions. The simulation was carried out for the summer (February) and winter (August) conditions of the Southern Hemisphere for the climatic period from 1993 to 2012. It is shown that, despite strong winds over the Southern Ocean, the geostrophic factor is usually much stronger than the wind-driven factor. Nevertheless, the contribution of the wind-driven component to the increase in the near-surface zonal velocity can reach 15-20% of the geostrophic velocity. The wind contributes to a decrease in the mean dynamic topography (MDT) from the open ocean to the coast of Antarctica. The influence of wind on the formation of the barotropic streamfunction of the current is more pronounced than on the MDT. Geostrophic transfer to the ACC is almost the same in winter and summer. Due to the effects of wind, the total transport of ACC around Antarctica increases by an average of 10-15 Sv in summer and 15-20 Sv in winter. The three-jet structure of the ACC was confirmed using numerical modeling using the "diagnosis-adjustment" method according to EN4 data. It is shown that the three-jet structure of the ACC has a geostrophic nature.

A. V. Isaeva

In this paper, retrograde condensation is considered using binary mixtures of hydrocarbons as an example. The possibility of numerical simulation of this phenomenon using the direct energy minimisation is demonstrated. To verify the calculations performed, similar modelling is carried out using the “classical” iterative algorithm for calculating vapour-liquid equilibria of multicomponent mixtures of hydrocarbons. A comparison of the simulation results, as well as the data of physical experiments, allows us to conclude that the method of direct energy minimisation is promising for calculating phase transitions of hydrocarbon mixtures.

B. A. Matiushin$^1$, V. I. Zakharov$^{1,2,3}$, N. A. Suhreva$^{1,4}$, O. V. Shestakov$^5$

We present the results of the study of systematic errors of the ionospheric model NeQuick 2, the verification of which was carried out on the data of satellite measurements of electron concentration of the Swarm mission for 2014. The measurements performed by Langmuir probes installed on the spacecraft of this mission during the period of solar activity maximum were used in this work. The conducted research made it possible to determine the average modeling errors in different latitude zones and geomagnetic conditions and to obtain the spatial distributions of systematic deviations of the model from the measurement data. The characteristic values of deviations are up to 80%, and in the conditions of geomagnetic disturbance the error in certain geographical areas increases up to 300%. The zones of increasing systematic deviations are observed in the high latitudes of the southern hemisphere. The results of the work can be useful for the operation of radio facilities and various applications, for example, to improve navigation and communication and to refine models of the ionosphere.

E. V. Koldoba

In some pressure and temperature ranges, high-precision thermal equations of state have many roots, and only one of them is the desired solution to the problem. The paper considers methods for setting initial values ??to find the desired root of the equation. A method for checking the found root has been developed, which allows one to exclude non-physical roots. The proposed approach allows one to construct a robastness algorithm for the numerical solution of transcendental equations of state.