Vol 124, No 2 (2023)

The features of the magnetic state of an array of parallel oriented permalloy ribbons are discussed. The arrays are made by explosive lithography. The ribbons have a thickness of 180 nm, a width of 2.8 μm, and a length of about 4 mm. The distance between ribbons in different samples varies in the range from 300 nm to 4 μm. It is found that the ribbons in the regions far from the end faces are in a single-domain state with small-angle ripples, the magnetization distribution of which correlates with inhomogeneities of the ribbon side surfaces. Moreover, there is a distinct relationship in the spatial distribution of the ripples between adja-cent ribbons with a relatively small distance between them. This makes it possible to evaluate the role of the magnetostatic coupling of magnetic subsystems of array elements and to estimate the characteristic value of the random stray field that pins the magnetization.

Nanocomposites (CoFeB)x(LiNbO3)100 – x with x = 17–48 at % have been synthesized by ion beam sputtering of a composite target comprised of Co40Fe40B20 and LiNbO3 onto silicon substrates, and the tran-sitions from the superparamagnetic state to the superferromagnetic and ferromagnetic states with an increase in the concentration of the magnetic component are studied by magneto-optical methods. The magneto-optical properties have been investigated in the geometry of the equatorial (transverse) Kerr effect (TKE). Magneto-optical spectra are recorded in the range of 0.5–4.0 eV in fields up to 2.5 kOe at 20–300 K, field and temperature dependences of the TKE at certain wavelengths are obtained, and the domain structure during magnetization reversal is visualized using a magneto-optical Kerr microscope. It is shown that the sample with x = 17 at % is superparamagnetic at temperatures above the blocking temperature (about 30 K). The interaction between the granules is considerable already at x = 20 at %, the transition to the superferro-magnetic state occurs at x ≈ 32–36 at %, and the transition to the ferromagnetic state occurs at x ≈ 44 at %near the metal–dielectric transition, i.e., at a concentration below the percolation transport threshold.

The effect of atomic configurations on the magnetic and structural properties of Fe2NiZ (Z = Al, Ga, In, Sn) Heusler alloys has been studied within the density functional theory. The competition between five structural motifs of the cubic phase due to permutations of Fe and Ni atoms is discussed. A new structure of the cubic phase with layer-by-layer atomic ordering of Fe and Ni atoms in the ground state is predicted. In this structural modification, the considered compounds have high magnetocrystalline anisotropy values that several times exceed the values for the FeNi alloy with tetragonal symmetry.

In this paper, we studied substituted lanthanum orthoferrite La0.67Sr0.33FeO3– γ by Mössbauer spectroscopy using X-ray diffraction data. A series of vacuum annealings was performed in the temperature range of tann = 200–650°C, after which no significant changes in the structure of the samples were detected. The Mössbauer measurements at room temperature show that the Fe ions are in an average valence state
between Fe3+ and Fe4+. Upon vacuum annealing, as the temperature tann increased, the average hyperfine magnetic field on the 57Fe nuclei and the isomer shift of the spectrum increased, which is associated with an increase in the number of vacancies and, accordingly, a decrease in the amount of Fe4+. Mössbauer measure-ments at 85 K showed that the average valence state of iron does not manifest itself. The hyperfine parameters of the low-temperature Mössbauer subspectra obtained from the model interpretation indicate that one of them belongs to Fe4+ ions, and the rest belong to Fe3+. The presence in the spectra of several sextets related to Fe3+ ions is due to the appearance of oxygen vacancies (breaking of the Fe3+–O2––Fe exchange bond) and Fe4+ ions (weakening of the Fe3+–O2––Fe exchange bond) in the nearest ionic neighborhood of Fe atoms. Both factors cause a decrease in the hyperfine magnetic field and a change in the isomer shift of the spectrum. As a result of model interpretation of the Mössbauer spectra, the numbers of oxygen vacancies and Fe4+ ions per formula unit depending on vacuum annealing temperature tann were determined for all samples. It was
shown that at tann above 450°C, the process of oxygen leaving the lattice ends and only Fe3+ ions are detected.

Within the model of two-phase (core/shell) ellipsoidal nanoparticles, the effects of the interfacial exchange interaction, size, elongation, and orientation of the major axes of the core and shell on the meta-stability of magnetic states have been simulated. Using the example of Fe2.44Ti0.56O4 nanoparticles,Fe3O4 it is shown that the metastability of magnetic states is realized in a limited range of the constant of interfacial exchange interaction between the core and shell, Ain , and geometric parameters. With an increase in the absolute value of the interfacial exchange interaction constant, , from Ain = 0 to some finite value, theAin metastability of magnetic states decreases monotonically from maximum to zero, regardless of the angle between the major axes of the core and the shell.

The theoretical microscopic consideration of antisymmetric exchange in iron garnet crystals sub-jected to inhomogeneous deformation shows that the resulting inhomogeneous magnetoelectric effect causes electrically induced phenomena that are experimentally observed in domain walls of iron garnet films. In addi-tion, the gradient of epitaxial strains is sufficient for development of chiral magnetic structures in these films.

A theory of spin and charge transport in bounded metallic magnets has been constructed, which takes into account the effects of spin-orbit scattering of conduction electrons by crystal lattice defects. The theory can be used to describe the spin Hall effect and the anomalous Hall effect and can serve as a basis for describing the phenomena of spin-orbitronics. Phenomenological boundary conditions for the charge and spin fluxes at the interface between two different metals have been formulated, on the basis of which the injec-tion of a pure spin current into a helimagnet, which arises in a normal metal as a manifestation of the spin Hall effect, is described. The existence of an “effect of chiral polarization of a pure spin current” is predicted, which consists in the appearance in a helimagnet of a longitudinally polarized pure spin current and a longi-tudinal component of the nonequilibrium electron magnetization, depending on the chirality of the helimag-net helix, upon injection of a transversely polarized spin current from a normal metal.

The possibility of partial substitution of Si for Ge in the structure of Bi2GeO5 during synthesis from the melt and the effect of the substitution on the structure of the synthesized material have been studied. The microstructure of the synthesized compounds after their complete decomposition has been investigated. Using the phase powder X-ray diffraction- and optical microscopy methods, it has been found that metasta-ble phases of bismuth silicate and germanate with structures of the Aurivillius type form a continuous series
of solid solutions. It is shown that a mixed structure composed of large Bi4Si(Ge)3O12 crystals and the Bi12Si(Ge)O20 + Bi4Si(Ge)3O12 point eutectic is obtained after the decomposition of compounds of the Bi2SiO5–Bi2GeO5 quasi-binary system, regardless of the percentage of substitution of Si for Ge. Upon slow heating up to annealing temperatures (at a rate of 13.5°C/min), a structure of decomposition that is more finely dispersed and uniform than the structure obtained upon rapid heating (when charg the material into an already preheated furnace), which is more coarsely grained and inhomogeneous. Moreover, regions with a large structure similar to a dendritic one can appear in the material when the contents of silicon and germa-nium oxides in the alloy are close to each other (20/30–30/20 mol %). Such regions differ slightly in chemical composition from the surrounding material and appear during both slow and rapid heating of the material to annealing temperatures.

The effects of nuclear transmutation in vanadium-based alloys under irradiation are considered in different reactor units including fast breeder reactors, such as (1) BOR-60 (experimental fast reactor), (2) EBR-II (experimental breeder reactor), and ITER (international thermonuclear experimental reactor). A comparison of nuclear transmutation rates for the analyzed [V–x% Cr(Ni)–y% Ti] alloys by data mining facilities is performed. It is demonstrated that the dominant types of interactions between neutrons and tested materials correlate with the level of thermalization in the neutron spectrum of a reactor, which has an effect on the value of nuclear transmutation rates to lead to distinctions in the resulting chemical composition of alloys after irradiation.

The structure and properties of coatings formed on 2ххх and 7ххх aluminum alloys by plasma elec-trolytic oxidation (PEO) performed under the same conditions have been studied. The substrate material is shown to substantially affect the quality, structure, and properties of formed coatings. Compared to the D16 Т (4Cu, 1.4Mg wt %) alloy substrate, the V95 Т1 (6.2Zn, 2.4Mg, 1.7Cu wt %) alloy substrate favors the for-mation of coatings with a more homogeneous composition and uniform thickness, which exhibit great cohe-sive and adhesive strength and mechanical and tribological properties. The adhesive failure of PEO coatings formed on the V95 Т1 alloy occurs at a load of 63 N, which is substantially higher than the critical load (49 N) of coatings formed on the D16 T alloy. The maximum hardness of coatings formed on the V95 Т1 alloy is 25 GPa, which exceeds that of coatings formed on the D16 T alloy and is equal to 20 GPa. The wear resistance of coating in water, which is formed on the V95 Т1 alloy is 4.4 times higher compared to that of the wear-resistant coating formed on the D16 T alloy.