The quasi-binary Y2(Fe0.29Co0.71)17 compound domain structure reconfiguration process is investigated over the entire sample thickness range. The domain structure bulk and surface patterns are identified using experimental techniques (magneto-optic and magnetic force microscopy) and micromagnetic simulations. The bulk domain reconfiguration is explained using classical theoretical models. The surface structures evolution is interpreted via the patterns complexity analysis. The magnetic moment rotation within the domain wall is studied through the micromagnetic simulations. The domain wall configuration is described and calculated.

The quasi-binary intermetallic compounds Y2(FexCo1 – x)17 and Y2(FexCo1 – x)17Hy exhibit easy-axis magnetocrystalline anisotropy in the iron concentration range 0.05 < x < 0.50. For compounds close to the edges of this range, at x = 0.03, 0.05, 0.41, 0.50, and 0.53, spin-reorientation transitions are realized. This paper presents a detailed study of these transitions based on the analysis of magnetocrystalline anisotropy energy function and micromagnetic analysis. Using the example of Y2(FexCo1 – x)17 and Y2(FexCo1 – x)17Hy compounds with spin-reorientation transitions, it is shown that, during the transition, the misorientation angles of the easy and hard magnetization axes, the magnetocrystalline anisotropy energy, and the domain wall energy reach their minimum values. The results of micromagnetic analysis of Y2(FexCo1 – x)17 and Y2(FexCo1 – x)17Hy indicate the existence of a domain structure in these compounds over the entire temperature range 0 < T < TC, including the phase transition point. The analytical temperature dependences of the surface energy density of the domain walls of the compounds exhibit a characteristic minimum in the phase transition region. The type of this minimum is determined by the second magnetocrystalline anisotropy constant.

The quasi-binary Y2(FexCo _1-x )17 compounds possess the easy-axis anisotropy type in a wide compositional range x = 0.05–0.50. The hydrogenation process of these compounds leads to a change in the magnetic characteristics—an increase in the Curie temperature and a variation in the values of the magnetocrystalline anisotropy constants. This work presents the complex investigation of the magnetic domain structure of both the original and hydrogenated samples of the Y2(FexCo _1-x )17 compounds. Qualitative comparative analyses and micromagnetic calculations were carried out.

The images of the magnetic domain structure (DS) stray fields were obtained in the basal plane of Nd2Fe14B and Y2(FexCo _1-x )17 (x = 0.18, 0.41) bulk uniaxial crystal samples at different tip–sample lift heights z using a magnetic force microscope. A method for automated evaluation of magnetic force microscopy (MFM) images is proposed. The average number of extrema per unit length (n) was calculated, n(z) dependences were plotted, and an analytical expression for approximating experimental dependences was derived. The n0 values, related to the z = 0 point, were obtained by approximating experimental data with the analytical expression. The values of the average domain width D and domain wall (DW) energy surface density γ were calculated based on the found n0 values.

The article presents the results of magnetocrystalline anisotropy (MCA) investigation of Y2(FexCo1-x)17 (x = 0.03-0.50) rare-earth quasi-binary bulk crystal samples and their hydrides. The specific magnetization curves m (H) were measured in the wide temperature range for the original Y2(FexCo1-x)17 samples and for the corresponding hydrides. Magnetocrystalline anisotropy constants K1, K2 were calculated, temperature and compositional dependence curves were plotted based on m ( H ) data. The temperature dependences of specific saturation magnetization m s ( T ) and first anisotropy constant K 1 ( T ) were analyzed to determine temperature behavior patterns, estimate the Curie temperature Tc and predict the spin-reorientation transitions. The first anisotropy constant, saturation magnetization and Curie temperature compositional dependences of original Y2(FexCo1-x)17 and hydrogenated Y2(FexCo1-x)17Hy samples were compared to identify the hydrogenation effect on the magnetic properties of investigated compounds. The revealed patterns were explained in terms of the crystal structure of the compounds.

The results of experimental studies of the magnetic properties and relaxation processes of the alloy Gd0,85Zr0,15(Co0,7Cu0,09Fe0,21)(6,0) are presented in this paper. The studied sample were subjected to a special heat treatment which allowed the formation of a certain nanostructure that affects the hysteresis properties of the material and allows to achieve a highly coercive state. The critical operating temperatures of the alloy were determined according to magnetic measurements at different temperatures performed on a vibrating magnetometer. It was found that thermal cycling of the sample in the range from 22 degrees C to 400 degrees C does not lead to changes in its magnetic properties at room temperatures. The investigations of magnetic viscosity effects allow us to conclude that the relaxation processes in the Gd-Zr-Co-Cu-Fe alloys are primarily due to the thermally activated overcoming of energy barriers by the domain walls, created by their complex and unique nanostructure. Metastable states of the domain structure near the barriers and their slow << release >> under the influence of the thermal fluctuations result in the observed slow change in magnetization over time after a change in the external magnetic field and/or temperature.

The paper presents the results of studying the microstructure, the magnetic domain structure and some magnetic properties of NiMnGaCu alloy samples in initial and deformed states. It has been shown that carrying out deformation-thermal treatment, including homogenizing annealing, extrusion with subsequent vacuum annealing, contributes to a change in the microstructure of the initial alloy (reduction in the size of crystallites and martensitic plates). Magnetic domains on the surface of the samples were visualized by magnetic force microscopy, and a substructure of secondary microtwins with their own magnetic domain structure was revealed. A study of the field dependences of the magnetization of the initial and deformation-heat-treated samples allows us to conclude that both samples have the same saturation magnetization value. Magnetometric measurements demonstrate an insignificant shift in the phase transition temperature towards lower temperatures for the deformed sample. The maximum values in the temperature dependences of the magnetocaloric effect for the original and deformed samples strictly correspond to phase transitions.

The work focuses on the study of the structure, phase composition, mechanical, electrical, and thermophysical properties, as well as the heat resistance and magnetocaloric effect of Fe2AlB2 MAB phase obtained by combining the self-propagating high-temperature synthesis and hot pressing. An investigation of the phase composition and structure of a consolidated sample disclosed that the main component of the ceramic is plate-like Fe2AlB2 grains with a thickness of 170-200 nm and a length of 2-5 mu m. The resulting single-phase hot-pressed ceramics exhibited hardness values up to 12.8 GPa, fracture toughness up to 5.2 MPa center dot m1/2, bending strength up to 429 MPa, and a thermal conductivity coefficient up to 7.47 W/(m center dot K). A differential scanning calorimetry analysis revealed that at a temperature of 1284 degrees C the complete decomposition of Fe2AlB2 occurred. The magnetocaloric effect measured by the direct method was 0.92 K at a Curie temperature of 291 K. The heat resistance of Fe2AlB2 was studied at 1000 degrees C. It has been established that the oxidation process is governed by a linear law, whereby a multilayer structure of a heterogeneous oxide film is formed on the surface of the sample. The surface layer of the oxide film consisted of hematite alpha-Fe2O3, while the inner layer comprised boron-containing oxides in the form of iron warwickite Fe2BO4 and a porous layer of aluminum borate Al4B2O9, formed as needle/wire-shaped crystals. The formation of a FeB-based sublayer at the interface with the substrate has been established. The calculated oxidation rate after 30 h of testing was 5.55 center dot 10-4 mg/(cm2 center dot s).

The effect of substitutional 4f-elements on the magnetism of rare-earth compounds RFe2-type with the Laves phase structure is studied to find new multifunctional materials, as well as to define the macro- and microscopic parameters of multicomponent magnets. The crystal structure of (Er,Y,Sm)Fe2 compounds is investigated by X-ray powder diffraction. Detailed information on the magnetic properties of the iron sublattice for multicomponent compounds with three different rare-earth elements is obtained for the first time by means of the 57Fe Mössbauer spectroscopy. The main regularities in the magnitude variation of magnetocaloric effect and magnetostriction (linear, anisotropic and volume) in varying composition of the (Er,Y,Sm)Fe2 compounds are determined.

The magnetization curves of the Y2(FexCo1 – x)17 compounds were measured in the temperature range of 300–923 K along easy and hard magnetization directions. The magnetization curves were analyzed, and the magnetocrystalline anisotropy constants K1, 2 of the samples were calculated. The temperature and composition dependences of the anisotropy constants K1, 2 and the saturation magnetization Ms were discussed. It was shown that, with increasing relative iron concentration in the samples, the first anisotropy constant K1 increases and reaches a maximum value of 5.1 × 105 J m–3 at x = 0.29.

The authors study the behavior of samples of (Gd,Zr)(CoCuFe)z alloy in magnetic fields oriented at different angles to their easy magnetization axes. The angular dependences of magnetization and coercivity are built. The hysteresis loops for the two main structural components of the samples are plotted using images of domain structure in demagnetizing fields. Results are analyzed by assuming there is a mixed mechanism of hysteresis in this family of alloys.

The authors study magnetic properties of Heusler alloys with composition Ni54.4Mn17.6Ga26.2Si1.8 subjected to multiple isothermal forging. It is found that multiple isothermal forging shifts the temperatures of structural and magnetic phase transitions toward low values. Magnetization and the magnetocaloric effect are reduced slightly, and there is a qualitative change in the structure of the magnetic domain.

This paper presents the results of complex studies, including direct experiment and computer modeling, of the magnetization reversal processes of a SmCo5 single crystal and a (GdBiLu)3(FeGa)5O12 ferrite-garnet film. The analysis of images of the domain structure in the external magnetic field of both samples allowed us to construct the field dependences of magnetization. It was found that the field dependence of the magnetization of the ferrite-garnet film coincides with the magnetometry data. For the SmCo5 single crystal the saturation field of the surface corresponds to the saturation field obtained from the measurements on a vibrating sample magnetometer, however, the view of the field dependence M(H) differs. Image analysis of the main domains of a single crystal in an external magnetic field and computer modeling have shown that the values of the domain structure disappearance fields on the surface of the film located above the single crystal are significantly less than the saturation fields according to magnetometry data. The application of an external magnetic field of 0,02 T leads to saturation of the entire volume of the ferrite-garnet film in the direction of the field, which does not allow further observation of the transformation of the main domain structure of the bulk sample and limits the applicability of the indicator film method.

The article continues a series of studies of permanent magnets with different magnetization reversal mechanisms (nucleation, domain boundary displacement). In this work, a correlation is established between magnetic characteristics of permanent magnets (Y25 and AlNiCo) and the fractal dimension of magneto-optical images of their stray fields. Bismuth-containing ferrite-garnet films were used as an indicator. It is shown that the limiting values of the fractal dimension: 1,76 for a ferrite magnet and 1,85 for an AlNiCo magnet, are consistent with the results obtained for NdFeB (grade N35) and SmCo (grade KC37) magnets, as is the behavior of the field dependence of the fractal dimension. The behavior of the field dependence of magnetization Mmo(Hrev) has similar features to a similar dependence recorded for a permanent magnet NdFeB (grade N35), but the values of the demagnetizing fields for the Y25 sample are much smaller. The paper discusses the relationship between the mechanisms of magnetization reversal of permanent magnets and the behavior of the Mmo(Hrev) dependence.

The heavy rare-earth-based Laves phases are well-studied intermetallic materials that stand out for their remarkably high magnetocaloric effects, particularly at cryogenic temperatures. In this study, we present the findings of our comprehensive investigation of cobalt Laves phases RCo2 with R standing for erbium, holmium, dysprosium, and terbium. This includes the determination of the magnetocaloric effect by indirect methods using calorimetric and magnetization data. Furthermore, for the first time in these materials, we directly measured the adiabatic temperature change at high magnetic fields up to 20 T. The largest Delta Tad value of 17 K, we obtained for ErCo2. Because the order of the transition significantly impacts the efficiency of thermodynamic cycles, we have also focused on determining the transition order in these materials. This was done through the application of established methods and a recently proposed quantitative criterion including the value of the local exponent n. Further, we compare our results with other materials using a straightforward material-based figure of merit - the temperature-averaged entropy change (TEC). Our results demonstrate the great potential of these materials for applications such as for magnetic hydrogen liquefaction.

New (Er1 – xYx)0.8Sm0.2Fe2 multicomponent alloys with a substitution parameter of x = 0, 0.2, 0.4, 0.6, 0.8, and 1.0 are synthesized and their atomic crystal structure and magnetic properties are studied. It is shown that full magnetic compensation can be expected in the region of 0.2 < xcomp < 0.4. Er0.8Sm0.2Fe2 alloy exhibits temperature-dependent magnetization compensation at Tcomp = 400 K.

The results of experimental studies of magnetic properties and magnetization reversal processes of a series of alloys Sm-Gd-Zr-Co-Cu-Fe are presented. The studied samples were subjected to prolonged isothermal annealing for 24 hours, which made it possible to achieve the formation of a certain nanostructure that affects the hysteresis properties of the material and allows to achieve a high coercivity state. According to the magnetic measurements data obtained by the method of a vibrating magnetometer, the hysteresis loops are constructed, the dependence of the saturation magnetization, and the coercive force on chemical composition, and the values of the temperature coefficient of magnetization change depending on the relative content of Sm and Gd are determined. It is shown that the substitution of a part of samarium atoms for gadolinium atoms increases the effect of the mechanism of irreversible rotation of the spontaneous magnetization vector on the remagnetization of samples. Application of the studied samples in various devices puts serious demands on the stability of their magnetic properties at high temperatures. Our researches allow us to conclude that compounds with gadolinium concentration x=0,5 have the greatest coercive force, and compounds with gadolinium concentration in the range x=0,5-0,6 have the highest temperature stability.

This work presents the results of a comparative analysis of the thermal, magnetic, magnetocaloric and magnetostrictive properties of the Dy0.42Ho0.42Tb0.16Co2, Dy0.5Ho0.5Co2 and TbCo2 compounds. All studied compounds have the MgCu2-type Laves phase structure at room temperature. Dy0.5Ho0.5Co2 and TbCo2 demonstrate first- and second-order transitions from a paramagnetic state to a magnetically ordered one, respectively. Special attention is given to determining the order of magnetic phase transition in a multicomponent compound with three rare earth elements (Tb, Dy and Ho). Features of the magnetocaloric effect and magnetostriction of (Tb,Dy,Ho)Co-2 compounds have been studied in magnetic fields up to 14 T and in wide temperature range (4.2 - 300 K). The joint manifestation of significant magnetocaloric and magnetovolume effects at the Curie temperature can be useful for a variety of technical applications.

The paper presents the results of the synthesis, structural studies, and investigation of the magnetic and magnetostriction properties of new multicomponent alloys based on heavy rare-earth metals ( R _1-x Y x ) 0.8 Sm 0.2 Fe 2 , where R = Tb, Gd, Dy, and Er, х = 0, 0.2, 0.4, 0.6, 0.8, and 1. It was found that alloys of these systems (except for the system with Tb) are single-phase and have the cubic С 15 Laves structure. The lattice parameters for all systems were shown to change linearly with increasing х . The main magnetic characteristics of the alloys were determined. The following practically important phenomena were found: the magnetic compensation of the sublattice magnetization, the spin reorientation, and the sign inversion of magnetostriction constants.