Magnetic properties of DyCo2 and HoCo2 have been investigated in both low and high magnetic fields up to 350 T. At low temperature, the compounds form ferrimagnetic structure with the rare-earth moments close to 10 mu(B) and a Co moment of similar to 1 mu(B). With increasing temperature, the magnetic disordering occurs through the first-order type transition, which confirms the itinerant nature of magnetism of d-electron subsystem of Co. From the field dependences of the voltage induced in the measuring coils of the explosive magnetocumulative generator, the values of critical field of metamagnetic transition in the Co sublattice from a field-disordered to a magnetically ordered state were determined to be 295 T and 329 T for HoCo2 and DyCo2, respectively. Using reliable literature data on the field of metamagnetic transition for the exchange-enhanced Pauli paramagnet YCo2, the values of molecular fields of the intersublattice exchange interaction and R-Co exchange coupling parameter were directly estimated. The obtained data are compared with those determined previously by indirect methods.

Raman spectra of the LaMn2Si2 compound were obtained for the first time by Raman spectroscopy. The change in the Raman spectral characteristics in the temperature range of 263–553 K was investigated. The high sensitivity of the Raman spectroscopy method to a change in the magnetic state caused by a temperature influence has been determined. A change in the spectral characteristics of the vibration mode of manganese atoms near the Curie and Neel temperatures has been revealed. The magnetic force microscopy technique was used to investigate the surface features of the LaMn2Si2 compound at room temperature. A change in the type of magnetic domain structure in LaMn2Si2 after cooling from 298 to 263 K has been found.

In magnetostrictive RFe2 (R – rare earth) materials, magnetic properties such as magnetocrystalline anisotropy and Curie temperature can have a profound impact on the magnetostriction, often reducing its value in practically applicable magnetic field at normal conditions. Tuning the atomic structure by Mn alloying is one of the research strategies that allows to improve both elastic and magnetoelastic properties. Here we investigate novel non-stoichiometric TbFe2Mnx (0 ≤ x ≤ 0.25) compounds in which Mn partially replaces both Tb and Fe. Curie temperature and magnetic moment values decrease with manganese alloying. We interpret these effects as a consequence of lowered Fe-Fe exchange interactions which is confirmed within two-sublattice molecular field model. Magnetocrystalline anisotropy estimated by law of approach to magnetic saturation in high pulsed magnetic fields shows trend of decrease with Mn doping. Notably, this cause significant increase of linear magnetostriction (up to 25%) for TbFe2Mnx compounds at liquid nitrogen temperature. Thermal expansion declined due to growth of magnetic contribution in magnetically ordered state, which is linked to volume magnetostriction. These changes make TbFe2Mnx promising material for practical application. Thus, it was shown that manganese alloying opens new way for tuning magnetocrystalline anisotropy and magnetostriction in non-stoichiometric Laves phase compounds.

Structure and magnetic properties of layered GdMn2(Ge1-xSix)2 (0 ≤ x ≤ 1) compounds were studied. All the compounds crystallize in the tetragonal ThCr2Si2-type structure. It was shown by magnetization measurements at low temperature on quasi-single crystals that, with increasing Si concentration, the easy magnetization direction reorients from the c-axis to the basal plane. The spin reorientation occurs via an angular phase. A model of three magnetic sublattices coupled by negative intersublattice exchange interactions was used to describe the field dependences of the magnetization. For GdMn2Ge2 and GdMn2(Ge0.9Si0.1)2 in the fields applied along the c-axis, seven different magnetic structures were predicted, including two angular structures considered for the first time. The model explains formation of angular magnetic structures in zero field in GdMn2(Ge1-xSix)2 system by taking into account magnetic anisotropy of Mn sublattices with a positive anisotropy constant K1 and negative K2.

Differential scanning calorimetry (DSC) is used to determine the magnetic phase transformation temperatures of the La1 – xYxMn2Si2 (x = 0–1) alloys. For the compositions with х from 0 to 0.3, the temperature dependences of DSC signal exhibit λ-like endothermic effects observed near 300 K, which are related to the magnetic phase transition from the ferromagnetic to layered antiferromagnetic structure, and weak anomalies, which are observed in a temperature range of from 458 K for the composition with х = 0 to 323 К for the composition with х = 0.3 upon disordering of the layered antiferromagnetic structure. A clear endothermic peak corresponding to the disordering of interplane antiferromagnetic layered structure was found for the YMn2Si2. The data obtained are used to construct the magnetic phase diagram of the La1 – xYxMn2Si2 system in a temperature range of 270–600 К. The differential scanning calorimetry is shown can be successfully used for the determination of temperatures of various magnetic phase transformations in rare-earth intermetallic compounds.

The features of magnetic microstructure of La0.73Dy0.27Mn2Si2 at 293 K have been visualized by atomic force and magnetic force microscopy. Magnetic force images reveal the presence of low-contrast magnetic domains. The change of Raman spectral characteristics of light scattering in the process of cooling La0.73Dy0.27Mn2Si2 to a temperature of 263 K is experimentally detected. The electronic structure of La0.73Dy0.27Mn2Si2 is investigated by resonance photoemission spectroscopy with the use of the synchrotron radiation. Resonances at the 3d and 4d levels of electronic structure show different properties of valence electrons. Using the Dy 3d–4f (M4.5 absorption edge) resonance, the distribution of 4f states of dysprosium in the valence band is determined. Photoemission upon the giant Dy 4d–4f (N4.5 absorption edge) resonance is determined by the contribution of all states in the valence band due to the sudden involvement of the Coulomb interaction. The energies of the 5p and 4f levels of La, the 4f level of Dy, and the 3d level of Mn in the valence band are determined.

This paper presents methods and approaches that can be used for production of Sm-Co-Fe-Cu-Zr permanent magnets with working temperatures of up to 550 °C. It is shown that the content of Sm, Cu, and Fe significantly affects the coercivity (Hc) value at high operating temperatures. A decrease in the content of Fe, which replaces Co, and an increase in the content of Sm in Sm-Co-Fe-Cu-Zr alloys lead to a decrease in Hc value at room temperature, but significantly increase Hc at temperatures of about 500 °C. Increasing the Cu concentration enhances the Hc values at all operating temperatures. From analysis of the dependence of temperature coefficients of the coercivity on the concentrations of various constituent elements in this alloy, the optimum chemical composition that qualifies for high-temperature permanent magnet (HTPM) application were determined. 3D atom probe tomography analysis shows that the nanostructure of the HTPM is characterized by the formation of Sm2(Co,Fe)17 (2:17) cells relatively smaller in size along with the slightly thickened Sm(Co,Cu)5 (1:5) boundary phase compared to those of the high-energy permanent magnet compositions. An inhomogeneous distribution of Cu was also noticed in the 1:5 phase. At the boundary between 1:5 and 2:17 phases, an interface with lowered anisotropy constants has developed, which could be the reason for the observed high coercivity values.

The structure and magnetic state of Fe100-xNix alloys (x & LE; 20) quenched from 1100 degrees C have been studied by means of Mo & BULL;ssbauer spectroscopy, X-ray diffraction, transmission electron microscopy, and magnetization measurements. The concentration dependences of the lattice parameter of bcc structure and of spontaneous magnetic moment were measured at room temperature. From the analysis of Mo & BULL;ssbauer spectra, concentration dependences of average hyperfine parameters have been determined. Both isomer shift and hyperfine field increase with increasing Ni content in the alloy. Fitting of the spectra with a set of subspectra gives grounds to conclude that the structure of quenched Fe-Ni samples represents a system of bcc regions of varying content, which is formed as a result of separation of the alloy composition. This conclusion is supported by the data of transmission electron microscopy.

Crystal structure, magnetostriction, magnetic and magnetothermal properties have been studied for novel non-stoichiometric ErFe2Mnx (0 <= x <= 0.6) compounds. It has been found that for x <= 0.4 the compounds crystallize with MgCu2-type structure. Curie temperature and magnetic moment values decrease with manganese alloying. Molecular field coefficients have been calculated within ferrimagnetic two-sublattice molecular field model. Magnetic and heat capacity measurements have been used to calculate magnetocaloric effect in a wide temperature range. It has been demonstrated that increasing the Mn content in ErFe2Mnx leads to a significant increase (up to 39 %) of anisotropic magnetostriction value at 77 K in magnetic field of 18 kOe. At the same time, the value of effective magnetocrystalline anisotropy decreases. Thus, manganese alloying opens new way for tuning magnetocrystalline anisotropy and magnetostriction in Laves phase compounds.

The electronic structure of the rare-earth intermetallic compound La0.73Tb0.27Mn2Si2 has been studied by resonant photoemission spectroscopy using synchrotron radiation, and its formation patterns have been established upon partial replacement of lanthanum atoms by terbium. The dependence of the valence band spectra shape on the photon energy near the absorption edges of the internal levels of manganese, lanthanum, and terbium is analysed. The processes of direct and two-stage production of photoelectrons, elastic and inelastic decay channels of these states with the emission of high-energy electrons due to intra-atomic Coulomb interaction have been studied. The dominant mechanisms of the decay of the excited states of the components under study were determined from the shapes of the spectra. For rare-earth metals elastic decay channel of the excited state is the most probable, while for manganese, it is inelastic, with the formation of a second hole in the valence band with subsequent enhancement of photoemission. Exciting photoemission near M5-absorption edges of rare-earth elements, the main contribution to the valence band comes from terbium 4f-states. Exciting photoemission near L3-absorption edge of manganese, the main contribution to the valence band is made by manganese 3d-states; with an increase in the photon energy in the region after resonance, an Auger channel for the decay of the excited state arises in the form of intensity maximum shift towards the binding energy growth. Features of the topography and magnetic domain structure of the La0.73Tb0.27Mn2Si2 surface were studied by atomic force and magnetic force microscopy at room temperature.

The electronic structure and optical properties of nonstoichiometric ErNi 2 Mn x compounds (with х = 0, 0.5, 1) have been studied. Spin-polarization calculations of the total and partial densities of electron states have been performed in terms of DFT + U method with a correction for strong electronic correlations in the 4 f shell of Er in the approximation of ErNi 2 – x Mn x solid-solution. The peculiarities of transformations of the densities of electron states Have been determined depending on the manganese content. The optical properties of these compounds have been studied over a wide wave length range. The calculated interband optical conductivity spectra have been compared with the dependences obtained experimentally. The origin of the quantum absorption of light is discussed. The plasma and relaxation frequencies of current carriers have been determined.

The electronic structure of the rare-earth intermetallic compound La0.73Tb0.27Mn2Si2 has been studied by resonant photoemission spectroscopy using synchrotron radiation, and its formation patterns have been established upon partial replacement of lanthanum atoms by terbium. The dependence of the valence band spectra shape on the photon energy near the absorption edges of the internal levels of manganese, lanthanum, and terbium is analysed. The processes of direct and two-stage production of photoelectrons, elastic and inelastic decay channels of these states with the emission of high-energy electrons due to intra-atomic Coulomb interaction have been studied. The dominant mechanisms of the decay of the excited states of the components under study were determined from the shapes of the spectra. For rare-earth metals elastic decay channel of the excited state is the most probable, while for manganese, it is inelastic, with the formation of a second hole in the valence band with subsequent enhancement of photoemission. Exciting photoemission near M5-absorption edges of rare-earth elements, the main contribution to the valence band comes from terbium 4f-states. Exciting photoemission near L3-absorption edge of manganese, the main contribution to the valence band is made by manganese 3d-states; with an increase in the photon energy in the region after resonance, an Auger channel for the decay of the excited state arises in the form of intensity maximum shift towards the binding energy growth. Features of the topography and magnetic domain structure of the La0.73Tb0.27Mn2Si2 surface were studied by atomic force and magnetic force microscopy at room temperature.

Differential scanning calorimetry (DSC) has been used to study the martensitic transformation in Fe100 – xNix alloys containing 3 to 25 at

The electronic structure of the rare-earth intermetallic La 0.73 Tb 0.27 Mn 2 Si 2 is studied by resonant photoemission spectroscopy using synchrotron radiation, and its regularities of formation are established upon the partial replacement of lanthanum atoms by terbium. The dependence of the shape of the valence-band spectra on the photon energy near the absorption edges of the internal levels of manganese, lanthanum, and terbium is analyzed. The processes of the direct and two-stage generation of photoelectrons, and the elastic and inelastic decay channels of these states with the emission of high-energy electrons due to intra atomic Coulomb interaction are studied. The dominant mechanisms of the decay of the excited states of the components under study are determined from the shapes of the spectra. For rare-earth metals the elastic decay channel of the excited state is the most probable, while for manganese, it is inelastic, with the formation of a second hole in the valence band and the subsequent enhancement of photoemission. Upon the excitation of photoemission near the M 5 absorption edges of rare-earth elements, the main contribution to the valence band comes from terbium 4 f states. In the case of the excitation of photoemission near the L 3 absorption edge of manganese, the main contribution to the valence band is made by manganese 3 d states; with an increase in the photon energy in the region after resonance, an Auger channel for the decay of the excited state arises in the form of a shift in the intensity maximum towards an increase in the binding energy. The features of the topography and magnetic domain structure of the La 0.73 Tb 0.27 Mn 2 Si 2 surface are studied by atomic-force microscopy and magnetic-force microscopy at room temperature.

In this paper, we studied TbFe2Mnx alloys using x-ray powder diffraction, x-ray fluorescent analysis, differential scanning calorimetry, scanning electron microscopy, and magnetostriction measurements. It was established that single phase non-stoichiometric TbFe2Mnx compounds are formed up to Mn concentration x = 0.25. The non-stoichiometric TbFe2Mnx compounds possess huge spontaneous magnetostriction in [111] direction (up to 2550 ppm) which result to distortion cubic MgCu2-type structure to rhombohedral (R-3m) at room temperature. The formation of non-stoichiometric TbFe2Mnx compounds results from partial substitution of Tb by Mn in (6c) positions. It was found a characteristic value for the cubic MgCu2-type lattice parameter ac ≈ 7.2 Å. If binary RT2 (R is a rare-earth metal, T – 3d transitional metal) compounds have lattice parameter smaller than 7.2 Å, we can expect large values of Mn concentration in non-stoichiometric RT2Mnx compounds. The Mn doping in TbFe2Mn0.25 compound led to significant increase of magnetostriction at liquid nitrogen temperature (λ|| ≈ 2400 ppm in magnetic field 18 kOe) which is 25% larger than that of initial TbFe2. It also preserve large magnetostriction at room temperature (λ|| ≈ 1530 ppm in magnetic field 18 kOe). This make non-stoichiometric TbFe2Mn0.25 compound promising material for various magnetostrictive applications in wide temperature range.

To specify what triggers the magnetostructural transition in CeFe2 doped with silicon, the temperature dependences of the magnetization, as well as the initial magnetic susceptibility and field dependences of the magnetization of the rare-earth intermetallic compounds Ce(Fe1 – xSix)2 with the silicon content x ≤ 0.05, were measured. The transition temperature to the magnetically ordered state and the average magnetic moment at Fe atoms were determined, and the magnetic contribution to the entropy change was estimated. Mössbauer spectra of Ce(Fe1 – xSix)2 (x ≤ 0.05) in the paramagnetic state were measured with a discretization of velocity scale of 512 channels, processing of which served to confirm the earlier suggested local ordering of Si atoms in the Fe sublattice.

The crystal structure, magnetic and magnetothermal properties of nonstoichiometric Er0.35Gd0.65Co2Mnx (0 <= x <= 0.4) compounds have been investigated. It is observed a considerable increase in the Curie temperature from T-C = 170 K up to above room temperature T-C = 324 K with increasing the Mn content. The exchange interactions in nonstoichiometric alloys of the RCo2Mnx-type (R is Er, Er0.35Gd0.65 and Tb) are determined within a two-sublattice mean field model. It is shown that increase in the Curie temperature of the RCo2Mnx - type non-stoichiometric alloys is associated with increasing of the magnetic moment and strengthening exchange in-teractions in the 3d-sublattice. The magnetization and heat capacity measurements were used to estimate the magnetocaloric effect in the compounds for the magnetic field change Delta H approximate to 20 kOe. It was found that com-pounds exhibit plateau-like temperature dependence of the field induced magnetic entropy change Delta S-m over a wide temperature range from 50 to 350 K and high values of Relative Cooling Power (up to 235 J/kg), the full width at half maximum of Delta S-m (Delta T-FWHM up to 310 K) and refrigerant capacity (RC up to 196 J/kg). The calculated and directly measured temperature variation of the adiabatic temperature change Delta T are found to be similar.

Electronic states on the surface of LaMn2Si2 and La0.75Sm0.25Mn2Si2 intermetallic compounds have been studied by resonant photoemission spectroscopy using synchrotron radiation, and the main regularities in the formation of the electronic structure upon partial substitution of samarium atoms for lanthanum have been found. The dependence of the shape of the spectra of the valence bands on the photon energy near the absorption edges of the internal levels of the components has been studied. The processes of direct and two-stage production of photoelectrons, elastic and inelastic channels of the decay of states with the emission of high-energy electrons due to intra-atomic Coulomb interaction have been studied. The features of the surface of the compounds at room temperature have been studied by atomic force and magnetic force microscopy. The presence of a complex magnetic domain structure in LaMn2Si2 in the case of partial substitution of samarium for lanthanum is also shown.

The structure and magnetic and magnetocaloric properties of nonstoichiometric ErM 2 Mn x alloys with M = Ni, Co, and Fe have been studied. ErNi 2 Mn x alloys with x ≤ 1.25, ErCo 2 Mn x alloys with x ≤ 0.8, and ErFe 2 Mn x alloys with x ≤ 0.4 are shown to solidify with the formation of the cubic MgCu 2 -type structure. The magnetocaloric effect of the ErM 2 Mn x compounds is estimated based on magnetic measurements and using the thermodynamic Maxwell’s relation. The ErFe 2 Mn 0.4 compound is found to demonstrate a plateau-like temperature dependence of the magnetic entropy change over the wide temperature range from 77 to 300 K.