


卷 120, 编号 3 (2019)
- 年: 2019
- 文章: 14
- URL: https://journals.rcsi.science/0031-918X/issue/view/10273
Electrical and Magnetic Properties
Macromagnetic Calculation of the Magnetization of a Deformed Ferromagnet
摘要
Research has been carried out on the dynamics of magnetization of a deformed ferromagnet in an external ac magnetic field. A microscopic model of a deformed magnetically soft ferromagnet has been suggested, based on the example of an α-iron crystal, which takes into account the Zeeman energy, the energy of interaction with the crystal field, and the magnetic dipole interaction of domains. The parameters of model Hamiltonians agreed with the experimental data on the magnetostriction of iron. Minimization of the functional of the density of the crystal energy by varying the magnetization of the sample made it possible to obtain an expression for the equilibrium magnetization of the ferromagnet in the approximation quadratic in terms of deformation. The numerical solution to the dynamic Bloch equation yielded a solution with the characteristic form of a hysteresis loop, the basic parameters of which depend on the amount of relative deformation of the sample. These numerical results were compared with the experimental data.



Charge States of Cations in Lithium–Nickel Phosphates LiNiPO4 Doped with Manganese and Cobalt
摘要
Using Ni, Mn, and Co L2,3-edge soft X-ray absorption spectra supported by calculations of atomic multiplets with allowance for the crystal field and charge transfer, the charge states of cations in doped phosphates LiNiPO4, LiNi0.9Co0.1PO4, and LiNi0.9Mn0.1PO4 are determined. It is established that nickel, manganese, and cobalt ions are in the divalent high-spin state and have an octahedral oxygen environment. Oxygen K-edge X-ray absorption spectra showed the absence of impurity states in the energy gap of manganese- or cobalt-doped lithium nickel phosphates.



Evolution of the Structure and Magnetic Properties of Ni@C Composite Nanoparticles upon Annealing
摘要
Nanopowders Ni@C synthesized by gas condensation have a core-shell structure. The size of the core is 2–10 nm and the thickness of the shell is 1–3 nm. The changes in the magnetic properties and the structure of these particles upon annealing in the 100–1100°C temperature range are investigated in this work. Analysis of changes in the magnetic properties, the structure, and the chemical stability shows that the core of the particles in the initial state after synthesis is a supersaturated solid solution of carbon in nickel, which decomposes into nickel and carbon upon high-temperature annealing. Rather slow cooling of nickel particles causes the carbon shell to form. The shell ensures their chemical stability.



Effect of Ferromagnetic Exchange and Magnetic Field Orientation on the Magnetocaloric Effect of Uniaxial Van Vleck Paramagnet
摘要
The magnetocaloric effect (MCE), namely, the magnetic entropy change upon the isothermal magnetization of a uniaxial Van Vleck paramagnet with a spin of S = 1 and single-ion easy-plane magnetic anisotropy has been studied in this work. It has been shown that, upon magnetization along the easy plane, the value of normal MCE (decrease in the entropy upon magnetization) can be anomalously high, when the ratio of anisotropy and ferromagnetic exchange parameters of a paramagnet is close to a threshold value corresponding to the transition to the ferromagnetic state. It has been found that, upon magnetization along the hard magnetization direction, i.e., perpendicular to the easy plane, the MCE at low temperatures demonstrates anomalous behavior, namely, the magnetic entropy increases upon magnetization.



Response of Magnetic Nanoparticles Lattice to Gaussian Pulse of Magnetic Field
摘要
Abstarct
The response of uniform and binary plane lattices of magnetic nanoparticles with uniaxial anisotropy to a short Gaussian pulse of magnetic field is studied in this work. It is shown that the dipole–dipole interaction and the presence of two types of nanoparticles modulate and decrease the response amplitude. The complicated periodic dependence of the amplitude and duration of the system response on the duration and peak value of the applied pulse has been discovered. The possibility of controlling the magnetization reversal of both the entire lattice and its parts by choosing the lattice composition and parameters of the bias field and pulse is demonstrated.



Ferromagnetic Resonance and Interlayer Exchange Coupling in (Fe/Cr)n Superlattices
摘要
The electromagnetic wave transmission in samples of Fe/Cr superlattices has been studied, for which the ferromagnetic resonance is observed in the magnetically unsaturated state. The transmission experiments have been performed at room temperature and at frequencies between 26 and 38 GHz. Ferromagnetic resonance spectra were measured. The interlayer exchange constants were estimated using magnetization curves. Ferromagnetic resonance spectra of acoustic branch were calculated using the values of exchange constants. The experimental and calculated resonance spectra have been compared.



Synthesis, Magnetic Properties, and Relaxivity of CoFe@C and NiFe@C Nanocomposites
摘要
Core–shell CoFe@C and NiFe@C nanocomposites were prepared by gas-condensation synthesis. CoFe@C and NiFe@C particles had bcc and fcc cores, respectively. The treatment of these nanocomposites with hydrochloric acid revealed that they are more chemically stable than Fe@C composites. The maximum specific magnetization of CoFe@C and NiFe@C nanocomposites at room temperature in the field with a strength of 27 kOe was 125 and 58 G cm3/g, respectively. The processes of longitudinal and transverse relaxation of nuclear proton spins of aqueous suspensions of nanocomposites in various magnetic fields (0.5, 1, and 2 kOe) were studied. NiFe@C and CoFe@C nanocomposites have high transverse relaxivity values and can be used as magnetic markers for detection of low concentrations of bioobjects by NMR relaxometry.



Structure, Phase Transformations, and Diffusion
Microstructure and Kinetics of Intermetallic Phase Formation during Solid State Diffusion Bonding in Bimetal Ti/Al
摘要
In this study, tri-layered Ti/Al composites were synthesized using hot press/roll bonding, and then the annealing treatment was executed in the temperature range of 550–650°C for 2, 4, and 6 h. Interfacial layers were characterized using scanning electron microscopes (SEM), energy dispersive spectrometer (EDS), and X-ray diffraction (XRD). The results of microstructural characterization for all annealing temperatures and times indicated that the Al3Ti compound is the only intermetallic compound observed in the diffusion layers. The Al3Ti growth obeyed linear kinetics and was characterized by an activation energy of 128.7 kJ mol–1. The results indicated that the dominant diffusing component was aluminum and the growth of the Al3Ti layer occurred mainly at Ti/Al3Ti interfaces.



Formation of Structure of a High-Speed Steel upon Laser Surface Melting
摘要
The effect of time and energy parameters of the pulsed laser treatment on the structure formation and hardness of high-speed steel upon surface melting after complete heat treatment has been studied. The results of the metallographic analysis and energy-dispersive X-ray spectroscopy of the steel, as well as of the microhardness measurements, have been discussed. It has been shown that the laser-induced remelting causes a significant refinement of both the dendritic structure of the solid solution and of the carbide constituent of the high-speed steel. The structure of the laser-affected zone and the morphology of dendrites depend on the laser treatment regimes.



Effect of the Rate of Shock-Wave Loading on the Structural and Phase Transformations of a Cr–Mn Nitrogen-Containing Austenitic Steel
摘要
Optical metallography, transmission electron microscopy, and EBSD analysis have been used to study the structural and phase transformations at various rates of shock-wave loading in the 0.4N–20Сr–6Ni–11Mn–2Mo–V–Nb (Kh20N6G11М2AFB) austenitic stainless steel. The shock deformation of the investigated steel at a rate of 471 m/s resulted in an increase in the density of dislocations to 8 × 1010 cm–2 and in the formation of ε martensite with a hcp lattice. An increase in the loading rate from 471 to 904 m/s at the initial room temperature led to a heating of austenitic steel samples without the formation of recrystallized grains but caused a reverse ε → γ transformation with inheritance of dislocations.



Accumulation of Defects in Austenitic Stainless Steels with Phosphorus and Titanium Additions upon Electron Irradiation at 573 К Investigated Using Positron Annihilation Spectroscopy
摘要
Using the positron annihilation spectroscopy method, the accumulation of vacancy-type defects in steels Kh16N15М3 and Kh16N15М3T1 alloyed with phosphorus has been studied at early stages of irradiation at a temperature of 573 К. The obtained data have showed that vacancies in the steels interact with phosphorus atoms at this temperature with the formation of immobile and low-mobile vacancy—impurity complexes, which results in the accumulation of vacancy-type defects. In the steel Kh16N15М3Т1 under irradiation, the formation of nanosized particles of intermetallic Ni3Ti precipitates occurs, which intensify recombination of point defects and reduce their accumulation as compared to the steel Kh16Н15М3. As this occurs, the presence of phosphorus in the steel Х16Н15М3Т1 likewise leads to the intensification of the accumulation of vacancy defects.



Strength and Plasticity
Effect of the Rate, Temperature, and Magnitude of Prestraining on the Parameters of Phase Transformations and the Thermomechanical Characteristics of the 45% Ti–45% Ni–10% Nb Shape Memory Alloy in Press-Formed Conditions
摘要
This work investigates the effect of the rate, temperature, and magnitude of the strain induced preliminarily to heating for developing shape memory effect on the phase composition, martensite transformation, phase transition temperature, lattice parameters, substructure parameters, and thermomechanic characteristics of the shape memory (SM) 45Ti–45Ni–10Nb (at %) alloy in the press-formed state. The relation between structural and thermomechanical parameters of the alloy is identified. The conditions of prestraining the SM alloy for achieving the best thermomechanic characteristics are determined. The results of this study have been used to develop a fire-protection device for nuclear power facilities.



Deformation Microstructure of a Copper Single Crystal after Loading by Spherically Converging Shock Waves
摘要
A layer by layer study of the structure of a 34-mm ball of a copper single crystal after loading by spherically converging shock waves has been performed using transmission electron microscopy. The deformation microstructure along directions \(\left\langle {100} \right\rangle \) and \(\left\langle {110} \right\rangle \) has been studied. It has been revealed that the character of the deformation microstructure substantially depends on both the direction of the shock-wave propagation and on the depth of the layer location in the sample. In the near-surface layers of the ball that are located perpendicular the \(\left\langle {100} \right\rangle \) direction, a well-pronounced cellular dislocation structure is present; in the layers located perpendicular to the \(\left\langle {110} \right\rangle \) direction, no formation of the cellular structure occurs; there is only a high density of homogeneously distributed dislocations. Regardless of the single-crystal orientation, microbands, microtwins, banded structures, and recrystallized grains are detected along with the dislocations. Dislocation vacancy loops are observed in all layers of the ball.



Metallophysical Foundations of Nanostructuring Frictional Treatment of Steels
摘要
The following materials-science aspects of the frictional treatment (FT) of martensitic and austenitic steels with sliding indenters were considered in this study: mechanisms of nanostructuring of iron alloys upon FT under sliding-friction conditions; strengthening, resistance to thermal softening, wear resistance, and mechanical characteristics of steels subjected to frictional and combined thermomechanical treatments; application perspectives of the nanostructuring FT in innovative technologies.


