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Vol 124, No 7 (2023)
ЭЛЕКТРИЧЕСКИЕ И МАГНИТНЫЕ СВОЙСТВА
Influence of High Content of Sodium Doping in Bi(Pb)2212 Superconductors
Abstract
We study here, the effect of high content of sodium doping on structural and electrical properties of Bi(Pb)2212 superconducting. The X-ray analysis results showed that all the prepared samples mainly belong to the superconducting tetragonal phase Bi–(Pb)2212. SEM micrographs show that the grains are closely related and have a characteristic flat shape for the superconductor Bi (Pb) 2212. For the undoped sample, the grains are randomly distributed with an average size of 5 μm. For doped samples, the morphology changes with sodium concentration. Resistivity measurements show that all samples have a superconducting character.
561-565
Magnetic Phase Transitions in Ultrathin YFeO3 Films According to Synchrotron Mössbauer Reflectometry Data
Abstract
The magnetic properties of ultrathin single-crystal Y57FeO3 orthoferrite films have been studied by Mössbauer reflectometry. Mössbauer spectra were measured using the ESRF synchrotron in the reflection geometry. As the temperature changes from 3.6 K to about 773 K, the splitting of the Zeeman sextet in the spectra successively decreases and, simultaneously, a quadrupole doublet appears in them, which indicates the development of a magnetic phase transition. From the temperature dependences of the magnetic hyperfine field Bhf for the main orthorhombic Y57FeO3 phase, Néel temperatures equal to TN ≈ 593 K, 562 K, and 567 K and the critical parameter values equal to β ≈ (0.28–0.3) ± 0.02 are determined in films with thicknesses of 28, 6.5, and 4 nm, respectively. An analysis of changing the ratio of the line intensities in the Zeeman sextet with temperature makes it possible to trace the successive rotation of the direction of the antiferromagnetic axes in Y57FeO3 toward the surface plane with an increase in the temperature and a decrease in the film thickness.
566-576
Simulation of the Three-Component Potts Model on a Hexagonal Lattice by the Monte Carlo Method
Abstract
Computer simulation of the three-component Potts model on a hexagonal lattice was carried out using the Monte Carlo method. Systems with linear dimensions L × L = N, L = 10–320 in units of interatomic distances are considered. Based on the theory of finite-size scaling, the static critical exponents of heat capacity α, susceptibility γ, magnetization β, and correlation radius ν are calculated. The data we obtained confirm that in the considered Potts model on a hexagonal lattice, a second-order phase transition is observed with critical exponents corresponding to the universality class of the three-component Potts model.
577-583
Calculating the Relative Variances of Magnetization, Heat Capacity, and Susceptibility in a Two-Dimensional Weakly Diluted Four-Component Potts Model
Abstract
The relative variances of the magnetization Rm, heat capacity Rc, and susceptibility Rχ are calculated by the Monte Carlo method in the spin lattice four-component weakly diluted Potts model on a square lattice at a spin density p = 0.80. It is shown that introducing a disorder in the form of nonmagnetic impurities into the 2D Potts model leads to nonzero values of Rm, Rc, and Rχ at the critical point. It has been found that these values decrease noticeably for systems with linear sizes L ≥ 120 interatomic distances.
584-587
Martensitic Transformation and the Electrical and Magnetic Properties of Ni51 – хMn36 + хSn13 (0 ≤ х ≤ 4) Alloys
Abstract
The structures and electrical and magnetic properties of Ni–Mn–Sn-based alloys are studied.
Changing the crystal lattice type in the course of martensitic transformation is found to be accompanied by substantial changes in the electrical resistivity. It is shown that for all the alloys under study negative magnetoresistance
is observed. The maximum magnetoresistance in a magnetic field of 18 kOe of ≈–45% was found
for the Ni47Mn40Sn13 alloy.
588-593
A System of Josephson Vortices in a Layered Electron-Doped Nd2 – xCexCuO4 Superconductor
Abstract
A brief review of the transport and galvanomagnetic properties of an electron-doped Nd2 – xCexCuO4 layered superconductor with an emphasis on the role of the structure of Josephson vortices formed in the crystalin a magnetic field oriented in the parallel direction to the CuO2 planes is given. The experimental data on the longitudinal and Hall magnetoresistance of the recently synthesized Nd2–xCexCuO4/SrTiO3 epitaxial films are analyzed. The possibility of formation of a system of Josephson vortices in this highly anisotropic system is determined by the unique orientation of the c axis and the conducting CuO2 planes of the Nd2 – xCexCuO4 compound with respect to the substrate plane.
594-607
The Electronic Structure, Thermoelectric, Optical Properties of Heusler Alloys Mn2MeAl (Me = Ti, V, Cr)
Abstract
The results of calculations of the electronic structure, thermoelectric characteristics, and an experimental study of the thermoelectric, electrical, and optical properties of Mn2MeAl Heusler alloys (Me = Ti, V, Cr) are presented. The agreement between theory and experiment in the sign of the Seebeck coefficient is shown. The obtained pattern of the band spectrum allows us to qualitatively explain the peculiarities of the temperature dependences of the electrical resistance and the permittivity dispersion.
608-615
СТРУКТУРА, ФАЗОВЫЕ ПРЕВРАЩЕНИЯ И ДИФФУЗИЯ
The Structure and Mechanical Properties of Rolled Sheets of the Multicomponent Al–2.5Ca–2.5Mg Alloy Doped with Scandium and Zirconium
Abstract
Using the Al–2.5% Mg–1% Mn–0.4% Fe base alloy (wt %) as an example, the effects of calcium, scandium, and zirconium additives (at about 2.5, 0.1, and 0.2 wt %, respectively) on the strength of rolled sheets has been studied. Ingots of the alloy of the chosen composition and the hot and cold rolled sheets obtained from them were used as objects for the experimental study. Based on microstructural studies, it is
shown that calcium binds iron into compact inclusions (presumably, into the Al10CaFe2 phases), which has a positive effect on the mechanical properties of the alloy, as well as on the technological plasticity during the
rolling operation. Zirconium and scandium additives make it possible to form thermally stable nanoparticles of the Al3(Zr, Sc)–L12 phase, which is favorable for maintaining a partially unrecrystallized structure in cold
rolled sheets during annealing at least up to 400°C. Using the alloy of the selected composition as an example, the fundamental possibility for producing sheet products from cast (unhomogenized) ingots with the properties of thermally hardenable alloys of the AlSiMgMn and AlZn4.5Mg1.5Mn types without using quenching has been demonstrated.
616-621
Change in the Radius of the First Coordination Sphere in Amorphous Alloys during Deformation
Abstract
Changes in the structure of amorphous alloys under deformation by high-pressure torsion, multiple-pass rolling, and pressure treatment have been studied using X-ray diffraction and scanning electron microscopy. It has been shown that under all types of deformation, shear bands are formed in amorphous alloys, which are regions of lower density compared to a surrounding undeformed amorphous matrix. Shear bands are regions of an increased free volume; the formation of bands results in steps occurring on the surface of samples. The number of shear bands and the surface morphology of deformed amorphous alloys are determined by the deformation type and physical properties of a material.
622-634
The Effect of High-Temperature Thermomechanical Treatment on the Microstructure and Mechanical Properties of Cu–Al–Ni–(B) Alloys with a Thermoelastic Martensitic Transformation
Abstract
Polycrystalline boron-alloyed α + β Cu–Al–Ni compositions subjected to high-temperature thermomechanical treatment (HTMT) via forging and rolling are studied for the first time. Optical, scanning, and transmission electron microscopy and X-ray diffraction analysis were used in combination with measurements
of tensile mechanical properties to study the peculiarities of the microstructure, phase composition, and mechanical properties of these alloys. The peculiarities of the microstructure and mechanical behavior of alloys differing in their aluminum and boron contents, which were subjected to HTMT, have been determined.
The alloys were prepared in the fine-grained state, which determines the increase in the functional strength and plastic characteristics. A schedule of HTMT of bulk Cu–Al–Ni–(B) alloys is proposed.
635-643
Secondary Phases in MgB2 Superconducting Ceramics
Abstract
Secondary phases have been revealed in the course of development of approaches to obtaining the superconducting MgB2 ceramic. These secondary phases are identified, and the mechanisms of their generation are thoroughly discussed. It is shown that a complex of methods, including the optical microscopy in
the polarized light, scanning and transmission electron microscopy, provides opportunities for describing the secondary phases in the MgB2 ceramic, especially when they cannot be determined only by X-ray analysis.
644-652
ПРОЧНОСТЬ И ПЛАСТИЧНОСТЬ
Peculiarities of the Behavior of Point Defects under the Optoplastic Effect in Copper
Abstract
The authors previously discovered a new optoplastic effect and observed it under the action of a nanosecond UV laser pulse irradiation of subcritical intensity. In this paper it is shown that under this effect no microporesarise in the subsurface layer of metal. This proves the statement that swelling of metal under laser impactof moderate (subcritical) intensity occurs due to interstitial atoms migrating to the surface and not due to melting with formation of bubbles. At a abrupt cooling (for ~20 μs) interstitial atoms migrate to the surfaceby the Schottky mechanism due to abnormal mass transfer and the less mobile vacancies have no time to
coagulate with formation of micropores in the time of the process.
653-659
Structural Evolution of 10% Cr–3% Co Steel Microalloyed with Re and Cu during Creep Au 923 К
Abstract
Structural evolution of the tempered lath martensite of the 10% Cr--3% Co steel microalloyed with rhenium and copper with a low nitrogen content and a high boron content during creep at 923 K was investigated for the purpose of establishment of the rison of decrease in creep resistance of this steel under the low applied stress. The tempered martensite lath structure of 10%Cr-3%Co steel with an average lath size of 370 nm and a high dislocation number density of 2 ×1014 m–2 was observed after normalizing at 1323 K with the following tempering at 1043 K for 3 h. The structure was stabilized by M23C6 carbides, M6C carbides, and NbX carbonitrides. During long-term creep, the lath structure strongly experienced an evolution: the width of the martensitic laths increased significantly, dislocation density decreased, the Laves phase and Cu-enriched particles remarkably coarsen. Such structural evolution correlates with an appearance of creep strength breakdown on curves “Applied stress vs. Time to failure” and “Minimum creep rate vs. Applied stress”. Significant coarsening of the Laves phase particles and Cuenriched particles via formation of the large particles with sizes more than 250 nm along high-angle boundaries and full dissolution of the fine particles with sizes less than 50 nm along low-angle boundaries of martensite laths is considered to be the main cause of degradation of the creep resistance of the steel studied.
660-667
ПОПРАВКА
Приложение к статье М. Е. Мацнева и В. С. Русакова “Создание сложных многокомпонентных моделей мёссбауэровских спектров на примере исследования сверхтонких взаимодействий в квазибинарных сплавах со структурой фаз Лавеса”
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