The effect of various heat treatments on the magnetic properties and microstructure of magnets manufactured using low-oxygen technology from the (Nd,Pr)31.9Febal.(Co,Cu,Al,Ga)1.7B0.8 (wt

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.

The crystal structure, magnetic and magnetothermal properties of (TmxPr1-x)2Fe16.5Nb0.5 alloys were studied. Alloys with x = 0–0.4 crystallize into a rhombohedral structure of the Th2Zn17-type, and alloys with x = 0.6–1 crystallize into a structure of the LuFe9.5-type, which is a disordered variant of the hexagonal structure of the Th2Ni17-type. The concentration range of single-phase hexagonal compositions turned out to be wide in the system (TmxPr1-x)2Fe16.5Nb0.5 and equal to x = 0.6–1. The rhombohedral and hexagonal phases coexist only in one alloy x = 0.5, and the Curie temperatures of these phases differ unexpectedly greatly by 14.1 K. The lattice parameters, saturation magnetization, and magnetocaloric effect -ΔSM increase in the system as the Pr content increases. The refrigerant capacity RC = 78.7 J/kg in a field of 15 kOe for an alloy with x = 0.5, in which two peaks -ΔSM(T) overlap, is the maximum in the system. The Curie temperature in the system increases nonmonotonically from 312.3 K for Pr2Fe16.5Nb0.5 to 346.2 K for Tm2Fe16.5Nb0.5 and deviates maximum from the linear dependence for x = 0.8. Apparently, this deviation of TC(x) is due to the influence of the internal pressure determined for the (TmxPr1-x)2Fe16.5Nb0.5 alloys by X-ray diffraction analysis.

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.

New intermetallic compounds GdMn1-xRuxSi, x = 0-1 with a tetragonal structure of the CeFeSi-type (P4/nmm) have been synthesized. For GdMn1-xRuxSi, Curie temperature TC drops sharply from 320 K (x = 0) to 78.3 K (x = 1), while the magnetocaloric effect varies from 1.84 J/kgK (x = 0) to 4.94 J/kgK (x = 1) with a change in the magnetic field of 0-17 kOe. Thus, the GdMn1-xRuxSi magnetic refrigeration compounds operate at temperatures from 320 K to 78.3 K, close to the nitrogen liquefaction temperature of 77.4 K. Therefore, the GdMn1-xRuxSi system, where x ranges from 0 to 1, could be of practical interest for nitrogen liquefaction, provided that these alloys are assembled into a cassette with a single large refrigerant capacity. The electronic structure and magnetic moments of the GdMn1-xRuxSi intermetallic compounds were calculated using the DFT + U theoretical method.

•The Curie temperature varies nonmonotonically in the (TmxPr1-x)2Fe16.5Nb0.5 system.•Apparently, it is due to the internal pressure in the alloys.•The reason for this behavior is the defected crystal structure of LuFe9.5-type.•Nb alloying significantly affects the magnetic and structural properties of alloys.

The crystal structure, magnetic and magnetothermal properties of (TmxPr1-x)2Fe16.5Nb0.5 alloys were studied. Alloys with x = 0-0.4 crystallize into a rhombohedral structure of the Th2Zn17-type, and alloys with x = 0.6-1 crystallize into a structure of the LuFe9.5-type, which is a disordered variant of the hexagonal structure of the Th2Ni17-type. The concentration range of single-phase hexagonal compositions turned out to be wide in the system (TmxPr1-x)2Fe16.5Nb0.5 and equal to x = 0.6-1. The rhombohedral and hexagonal phases coexist only in one alloy x = 0.5, and the Curie temperatures of these phases differ unexpectedly greatly by 14.1 K. The lattice parameters, saturation magnetization, and magnetocaloric effect -Delta SM increase in the system as the Pr content increases. The refrigerant capacity RC = 78.7 J/kg in a field of 15 kOe for an alloy with x = 0.5, in which two peaks -Delta SM(T) overlap, is the maximum in the system. The Curie temperature in the system increases nonmonotonically from 312.3 K for Pr2Fe16.5Nb0.5 to 346.2 K for Tm2Fe16.5Nb0.5 and deviates maximum from the linear dependence for x = 0.8. Apparently, this deviation of TC(x) is due to the influence of the internal pressure determined for the (TmxPr1-x)2Fe16.5Nb0.5 alloys by X-ray diffraction analysis.

Ag doped Bi2O3 nanopowders (NPs) were produced by pulsed electron beam evaporation (PEBE) under vacuum. The solid phase synthesis in an electric furnace on air was used for silver doping of bismuth oxide. Different physicochemical properties of NPs have been studied. The specific surface area of (SSA) Ag- Bi2O3 NPs was 23.7 m2/g. Air annealing (200 °C) caused decreased crystallinity and an increase in the SSA of both pure and Ag-doped bismuth oxide. The dominant phase in not annealed/annealed Ag doped Bi2O3 NPs at 200 °C and 300 °C was β -phase Bi2O3. The thermal stability of the pure and Ag-doped Bi2O3 NPs was maintained at 300–350 °C. The phase transition β→α occurred with a further increase in temperature. The annealing temperature could effectively change the physicochemical properties of the Bi2O3 NPs.

The reaction of C6-unsubstituted 5-aryl-3-(2-pyridyl)-1,2,4-triazine with generated in situ difluoroaryne intermediate (4,5-difluoro-1,2-dehydrobenzene), previously unused for this aim, was studied. New transformations of the 1,2,4-triazine nucleus were discovered, which lead, along with the domino transformation product (10-(1,2,3-triazole-3-yl)pyrido[1,2-a]indole) natural for this transformation, to the formation of unexpected products, namely 1,3,5-tris-substituted 1,6-dihydro-1,2,4-triazin-6-ol and 1H-1,2,4-triazole. The structure of the products was confirmed by physicochemical methods, including X-ray diffraction analysis.

Five representatives of 4,5-diaryl-substitted 3-hydroxy-2,2′-bipyridine-6-carbonitriles were studied by single-crystal X-ray diffraction. The specific features of the molecular structures of these compounds and the effect of substituents on the crystal packing are discussed. The results of this study may be of interest in terms of the possible biological activity of this series of compounds and their use as polydentate N,N- or N,O-type ligands.

A novel method for the synthesis of 1,2,4-triazolo[1,5-d][1,2,4]triazine-2-amines by solvent-free thermolysis of the 1H-tetrazole-5-amine in presence of the 1,2,4-triazine-5-carbonitriles has been proposed. A mechanism of found interaction has been suggested.

New samarium complex of 5-phenyl-2,2'-bipyridine with the diethylenetriaminotetraacetic acid (DTTA) residue in the C6 position, [(L2)Sm2Na5(H2О)9(C2O4)]n (I), is synthesized. The structure of complex I is studied by XRD (CIF file CCDC no. 2217968). The complex in the crystal is found to be a one-dimensional coordination polymer, and the 2,2'-bipyridine fragments do not chelate the Sm3+ cation. The complex is characterized by a luminescence response to the addition of an excess of zinc cations.

This work is devoted to the study of the magnetic properties and Electron Paramagnetic Resonance (EPR) spectroscopy of TiO2:Fe nanoparticles doped with Al in different structural states. The sol-gel methods have been used to obtain the particles in both crystalline (average size from 3 to 20 nm) and X-ray amorphous states. The electron paramagnetic resonance spectra of crystalline samples TiO2:Fe doped with aluminum besides a resonance line with g-factor ~2 exhibit a small signal with a g-factor of 4.3 from Fe3+ ions with rhombohedral distortions. The fraction of Fe3+ with rhombohedral distortions increases with increasing aluminum content. For the amorphous state at Al doping, the resonance with a g-factor of 4.3 is completely dominant in the electron paramagnetic resonance spectrum. The density functional theory calculation shows that aluminum prefers to be localized near iron ions, distorting the nearest Fe3+ environment. The complex integral electron paramagnetic resonance spectrum of all samples was fitted with sufficient accuracy by three separate resonance lines with different widths and intensities. The temperature behavior of the electron paramagnetic resonance spectrum can be described by the coexistence of paramagnetic centers (isolated Fe3+ ions including dipole-dipole interactions) and iron clusters with negative exchange interactions.

Recently we described the solvent-free interaction of 5-aryl-3-(2-pyridyl)-1,2,4-triazine-5-carbonitriles and 2-amino-4-aryloxazoles to form 4,5-diaryl-3-hydroxy-2,2'-bipyridine-6-carbonitriles. It turned out that under absolute (anhydrous) conditions this reaction resulted in the formation of two products, namely, the previously described 4,5-diaryl-3-hydroxy-2,2'-bipyridine-6-carbonitriles (yields up to 44%) and 4,5-diaryl-2,2'-bipyridine-6-carbonitriles (yields up to 32%).

Sm(Fe,Co,Ti)12-based alloys with low contents of rare-earth elements are promising materials for manufactoring high-energy permanent magnets. The (Sm,Zr)(Fe,Co)10.3Ti0.7 alloy has been produced by strip casting with low quenching rates. The structure and magnetic properties of the alloy were studied by scanning electron microscopy, as well as X-ray and thermomagnetic analysis. The initial inhomogeneous alloy was subjected to solid-solution treatment at 1150°С. The alloy retained a high-anisotropy state typical of the Sm(Fe,Co,Ti)12 phase.

In this paper, the electron and magnetic state of iron placed either on the surface or in the core of TiO2 nanoparticles were investigated using magnetometric methods, electron paramagnetic resonance (EPR) and Mössbauer spectroscopy. It was demonstrated that the EPR spectra of TiO2 samples with iron atoms localized both on the surface and in the core of specific features depending on the composition and size of the nanoparticles. Theoretical calculations using the density functional theory (DFT) method demonstrated that the localization of Fe atoms on the surface is characterized by a considerably larger set of atomic configurations as compared to that in the core of TiO2 nanoparticles. Mössbauer spectra of the samples doped with Fe atoms both on the surface and in the core can be described quite satisfactorily using two and three doublets with different quadrupole splitting, respectively. This probably demonstrates that the Fe atoms on particle surface and in the bulk are in different unlike local surroundings. All iron ions, both on the surface and in the core, were found to be in the Fe3+ high-spin state.

We previously reported the solvent-free reaction of 5-aryl-3-(pyridin-2-yl)-1,2,4-triazine-5-carbo­nitriles with 2-amino-4-aryl-1,3-oxazoles, which afforded 4,5-diaryl-3-hydroxy-2,2′-bipyridine-6-carbonitriles. Similar reaction in anhydrous medium led to the formation of two products, previously described 4,5-diaryl-3-hydroxy-2,2′-bipyridine-6-carbonitriles (up to 44%) and 4,5-diaryl-2,2′-bipyridine-6-carbonitriles (up to 32%).

The structure and electrical properties of the Cu-5.9 at.% Pd alloy were studied after its annealing for two months at 250 degrees C. As a result of such a long-term thermal treatment, in the XRD patterns taken from the alloy one can observe a weak superstructural (100) reflection, which seems abnormal, since the alloy can only be in the state of a disordered single-phase solid solution (as it follows from the generally accepted Cu-Pd phase diagram). Quantitative analysis of the X-ray diffraction patterns reveals the presence of two new phases with different contents of Pd. An assumption is made that L12 superstructure can be formed in the Pd-enriched phase. The specific features observed in the temperature dependence of electrical resistivity, as well as the TEM results, confirm this set-forth hypothesis of ours. Using the resistometric method, the temperature of the order-disorder phase transition in the alloy was estimated as Tc approximate to 340 degrees C. It is concluded that the position of the A1-(A1+ L12) phase boundary in the Cu-Pd phase diagram requires more precise definition in the region of compositions on the side of the low Pd content.

The GdFeAl compound contains 42.8 wt% of the cubic phase of the MgCu2 (Fd3m)-type and 57.2 wt% of the hexagonal phase of the MgZn2 (P6(3)/mmc)-type, the GdFeSi compound is a tetragonal of the CeFeSi (P4/nmm)-type phase, the GdCrAl and GdVAl compounds do not exist. In the GdFeAl1-xSix, GdFe1-xCrxAl and GdFe1-xVxAl substitutional compounds, the content of the cubic phase sharply increases and amounts to 62.3%, 99% and 99%, respectively, for the composition x = 0.2. The Curie temperature T-C(x) increases for the hexagonal and cubic phases in GdFeAl1-xSix, while for the tetragonal phase it decreases with increasing x. These various changes of T-C(x) are uniformly explained by the corresponding various changes of the density of states at the Fermi level N (E-F) in the model of exchange interaction between the R and 3d ions in R-3d intermetallics, in which T-c similar to N(E-F). Ab initio calculations of N(E-F) for the cubic, hexagonal and tetragonal phases in the GdFeAl1-xSix compounds have been carried out. The T-C(x) decreases in the GdFe1-xCrxAl and GdFe1-xVxAl systems for the hexagonal and cubic phases with increasing x. The saturation magnetization increases in the GdFeAl1-xSix, GdFe1-xCrxAl and GdFe1-xVxAl systems as x increases.

The intermetallic compounds GdFe1-xCrxSi, x = 0-0.8, GdFe1-xVxSi, x = 0-0.4, and GdFe1-xNixSi, x = 0-0.4 with a tetragonal CeFeSi (P4/nmm) structure type have been synthesized. The Curie temperature, TC, sharply increases from 130 K to 255 K and 250 K for the GdFe1-xCrxSi and GdFe1-xVxSi compounds and decreases to 104 K for GdFe1-xNixSi. Within the framework of the model of effective d-f exchange interaction in R3̄d intermetallics, these changes in TC can be caused by the corresponding changes in the density of states. The electronic structure, magnetic moments and types of magnetic orderings of the GdFe1-xTxSi, T = Cr, V, Ni intermetallic compounds were calculated using the DFT+U theoretical method. For the GdFe1-xNixSi system, the transformation of a ferromagnet with the composition x = 0 into an antiferromagnet with the composition x = 0.3 was established experimentally and using first-principles calculations. The correlation of the ferromagnetic or antiferromagnetic type of the magnetic state in the GdFe1-xNixSi compounds with the value of the lattice parameter c to greater or less than the critical value c = 6.72 Å for the GdCoSi antiferromagnet has been experimentally established. The magnetic structures of the antiferromagnets GdFe0.7Ni0.3Si and GdCoSi were found to be different. GdFe0.7Ni0.3Si is characterized by a collapse in the magnetocaloric effect via a change in the isothermal magnetic entropy ΔSM(TC). The compounds GdFe0.4Cr0.6Si with -ΔSM(TC) = 2.37 J kg-1 K-1 at TC = 255 K and RC = 82.07 J kg-1 and GdFe0.7V0.3Si with -ΔSM(TC) = 2.06 J kg K-1 at TC = 250 K and RC = 96.02 J kg-1 in a field changing to 17 kOe could be of practical interest due to the TC being close to room temperature.