Fizika metallov i metallovedenie

The structural and magnetic properties of V₇Se₈ chalcogenide were studied using X-ray diffractometry, magnetic susceptibility measurements and nuclear magnetic resonance (NMR) spectroscopy on ⁵¹V nuclei. The ordering of vacancies in vanadium cationic layers with the formation of a 4C-type superstructure was found. It is estimated that the effective magnetic moment of vanadium ions is µ_eff = 0.35 µB. A significant local charge and magnetic heterogeneity of the V₇Se₈ compound has been revealed. The hyperfine interaction constant in vanadium ions is estimated from the temperature dependences of the magnetic shift of the NMR ⁵¹V line and the susceptibility χ(T) in V₇Se₈. A joint analysis of the NMR line shift data and the spin-lattice relaxation rate of ⁵¹V showed that the 3d-electrons of vanadium are in a itinerant state. At the same time, with decreasing temperature in the V₇Se₈ system, antiferromagnetic correlations are induced between the magnetic moments of vanadium in adjacent layers.

Phase transitions for an open system consisting of an ensemble of interacting quantum subsystems with discrete spectrum are studied in the mean-field approximation. In the considered model, the change of an internal symmetry of a thermodynamic system upon the second-order phase transition is due to changing symmetry of distribution of charge/spin density inside each quantum subsystem. The latter can be caused by either splitting of one of lowest degenerated energy level or closing a gap between the levels and appearance of avoided crossing. The effect of external parameters (pressure, field, composition, etc.) results in direct change of internal control parameters: level spacing and/or the strength of interaction between adjacent quantum subsystems. Considering a simplest case of the two-level quantum subsystems, expressions for the free energy as a function of the internal control parameters were obtained in analytical form. The behavior of the heat capacity and susceptibility for different regions of the low-temperature phase diagram including the area of quantum fluctuations was determined.

In this work, thin carbon films were deposited on the surface of armco-iron using magnetron sputtering of a carbon target in an Ar⁺ working gas environment. Then the carbon films were implanted with argon and nitrogen ions. In order to clarify the content of differently hybridized (i. e., in different chemical states) carbon atoms in the deposited material, the method of analyzing the photoelectron energy loss spectra was used in this work. It is shown that the satellite structure of c1s spectra, when analyzed jointly with xps of the c1s core level, confirms the formation of a disordered structure of the carbon film and allows one to determine the mass density of thin carbon films.

In this work, we experimentally studied the structural modification of the interfaces in bilayer Co/Pt spintronic terahertz emitters under irradiation with He⁺ ions with a fluence of up to 10¹⁶ cm^-2. Using the non-destructive method of small-angle X-ray reflectometry, an increase in the Co/Pt interface width from 1.2 nm (initial sample) to 1.9 nm under irradiation with He⁺ with a fluence of 10¹⁶ cm^-2 was detected. The experimental data are in good agreement with the results of modeling using SRIM. The magneto-optical measurements showed that the samples retain their magnetic properties at all fluences. The results can be used to increase the efficiency of terahertz generation in such structures.

Within the framework of the dynamic theory of martensitic transformations, the possibility of cooperative growth of the faces of the resulting crystal is discussed using the example of the formation of a layer parallel to the habit plane. This growth is comparable to the lateral crystal growth typical of shape memory alloys, but not typical of α-martensite in iron alloys upon simple cooling. However, under conditions of external tensile stress, rapid lateral growth of thin-lamellar α-martensite crystals was observed. It is shown that the formation of a layer parallel to the habit plane is similar to the formation of the original crystal. The functions of the dislocation nucleation center (DNC*) for this layer are performed by a dislocation loop framing the habit plane with the Burgers vector b*, and b* is specified by the macroshift in the initial crystal. An example of a crystal with a habit close to (3 14 9) is considered. The results of calculation of the elastic field of the DNC* loop are presented using data on the elastic moduli of the Fe–31.5%Ni alloy at a temperature M_s = 239 K. In the approximation of longitudinal waves for a pair of relatively long-wave components in the control wave process, the practical coincidence of the layer habit with the initial habit is demonstrated. The value of b* has been estimated.

The thermal stability of thin wires made of aluminum alloys Al-0.25%Zr, additionally alloyed with Si, Er, Hf, Nb, was studied. Cast blanks were obtained by induction casting in vacuum; wire with a diameter of 0.3 mm was obtained by drawing with preliminary deformation treatment of the blanks. The effect of the annealing temperature on the mechanical properties and specific electric resistivity (SER) of aluminum wires has been studied. The microstructure of wires in the recrystallized state is investigated. It is shown that as the annealing temperature increases, there is a monotonous decrease in tensile strength, micro-hardness, and SER. It is established that the ductility of the wire does not monotonously (with a maximum) depend on the annealing temperature. Optimal annealing modes have been determined, providing the best combination of tensile strength, microhardness and SER of aluminum wire.

For the first time, deuterium retention in the welded seam of the domestic reduced-activation ferritic-martensitic (RAFM) steel EK-181 (Rusfer) was investigated in comparison with the usual samples of the same steel. The welded seam was obtained by the argon arc welding method of two sheets of steel EK-18 with a thickness of 2 mm. Samples were kept in gaseous deuterium at a pressure of 5 atmospheres and temperatures in the range of 623–773 K for 25 hours. The number of retained deuterium was determined by thermal desorption spectrometry (TDS). It was found that after exposure in the gas, samples carved from a weld retained about 2 times more deuterium than samples from conventional steel EK-181. The number of peaks in TDS spectra is the same for both ordinary steel and the area of the weld. The TDS spectra modeling was carried out using the TMAP7 code. The proposed model includes the presence of oxides on the surface and a high concentration of defects in the surface layer of samples, wherein well describing the experimental TDS spectra. The possible nature of hydrogen states in steel is discussed, which determines the features of TDS spectra.