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.

В статті вперше досліджені сорбційні властивості наночастиц TiO2 з рутиловою фазою; Наночастиці TiO2 із фазою рутила були синтезовані золь-гелевим методом і використані в якості адсорбента. Пізніше був вивчений процес адсорбції розчину фенола 1 мг/л у присутності наночастиц рутила TiO2. Процес адсорбції тривав 2 години при температурі 25° C. Установлено, що адсорбція фенола в присутності рутилової фази TiO2 є неповною. Хоча рутилова фаза TiO2 є дуже хорошим фотокатализатором, як було показано, проте вона є слабким адсорбентом. У цій статті представлено опис адсорбції фенола наночастицями TiO2. Нанокристалічні частинки рутилової фази TiO2 охарактеризовані методом порошкової рентгенівської дифракції (XRD). На основі кривих, побудованих на приладі «Varian Cary 50» було визначено, що адсорбція була неповною. По закінченню процесу спираючись на графік, можна зробити висновок, що кількість фенола в розчині зменшилася, але фенол ще залишився, що свідчить про неповну адсорбцію. Розроблено математичне моделювання процесу як логістичними, так і експоненційними методами.

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 properties of the selenide compound Fe7Se8 with a layered crystal structure of the NiAs type are strongly influenced by substitutions and the distribution of vacancies. The Cr-substituted compound Fe6.5Cr0.5Se8 was obtained in single-crystalline form and studied by x-ray diffraction, energy-dispersive x-ray spectroscopy, thermal expansion and magnetization measurements. It was observed that the partial replacement of iron with chromium led to a twofold decrease in spontaneous volume magnetostriction due to changes in competing magnetoelastic contributions to thermal expansion along and perpendicular to the c axis of the crystal. The replacement of iron with chromium slightly decreases the N & eacute;el temperature (from 440 to 435 K) and significantly enhances the critical temperature of spin reorientation transition T-sr (from 115 to 160 K), apparently due to a change in the crystal electric field. Below 160 K, the Fe6.5Cr0.5Se crystal is found to exhibit metamagnetic-like behavior of the magnetization when the magnetic field is applied along the c axis. A jump-like change of the magnetization at a critical field up to similar to 10 kOe is attributed to the presence of pinning centers of domain walls presumably due the ordering of chromium atoms substituting iron in cationic layers.

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.

The structures and electrical and magnetic properties of Ni–Mn–Sn-based alloys are studied. Changing the crystal lattice type in the course of martensitic transformation is found to be accompanied by substantial changes in the electrical resistivity. It is shown that for all the alloys under study negative magnetoresistance is observed. The maximum magnetoresistance in a magnetic field of 18 kOe of ≈–45% was found for the Ni 47 Mn 40 Sn 13 alloy.

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 ErNi2Mnx 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 4f shell of Er in the approximation of ErNi2 – xMnx 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 structures and electrical and magnetic properties of Ni-Mn-Sn-based alloys are studied. Changing the crystal lattice type in the course of martensitic transformation is found to be accompanied by substantial changes in the electrical resistivity. It is shown that for all the alloys under study negative magnetoresistance is observed. The maximum magnetoresistance in a magnetic field of 18 kOe of approximate to-45% was found for the Ni47Mn40Sn13 alloy.

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.

Abstract—In the Ni47Mn42In11 and Ni43Со4Mn42In11 alloys, structural and magnetic phase transformations were studied by the magnetometry, dilatometry, and structural analysis. The temperatures of structural and magnetic transitions of the Ni43Со4Mn42In11 alloy have been determined. It has been shown that cobalt doping significantly increases the difference between the martensitic transformation temperature and Curie temperature. It has been found that in this alloy the martensitic transformation is accompanied by jumps in the temperature dependences of linear thermal expansion.

The structures and electrical and magnetic properties of Ni–Mn–Sn-based alloys are studied.Changing the crystal lattice type in the course of martensitic transformation is found to be accompanied by substantial changes in the electrical resistivity. It is shown that for all the alloys under study negative magnetoresistanceis observed. The maximum magnetoresistance in a magnetic field of 18 kOe of ≈–45% was foundfor the Ni47Mn40Sn13 alloy.

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.