Magnesium orthovanadate Mg3V2O8 provides an excellent model for studying the transport of magnesium cations in a three-dimensional matrix with two types of Mg(1)O-6 and Mg(2)O-6 octahedra connected by edges and chains of VO4 tetrahedra isolated from each other. In the present paper, the magnesium cations have been found to be the ionic charge carriers in this system using the Tubandt method. The electrical conductivity (sigma) has been studied by the impedance spectroscopy in the range 770-1270 K. The activation energy of sigma (E-sigma) has been demonstrated to be 1.25 eV in the range 923-1023 K. For the first time, the V-51 NMR spectra have been obtained and analysed in the range 295-900 K. The activation energy (E-NMR) for the diffusive jumps of Mg2+ cations has been identified to be 1.03 eV by analyzing the temperature dependence of the V-51 spin-lattice relaxation. The smaller E-NMR value is due to the rapid movement of magnesium along the chains of Mg(2)O-6 octahedra. Large E-sigma value and low ionic conductivity indicate that the limiting step in Mg3V2O8 is the cation hopping between the chains of Mg(2)O-6 octahedra through the intermediate Mg(1) positions.

A comparative analysis of the composition and structure of freshly precipitated iron(III) hydroxide precipitates obtained from a sodium sulfate solution (400 mg/L) at pH 7 and 8 before and after the sorption of nickel ions on them was carried out. IR, Raman, and Mössbauer spectroscopy, as well as X-ray diffraction and thermal analyses, have shown that precipitates synthesized from a solution of iron(III) chloride are a two-line ferrihydrite with the gross formula Fe2O3⋅3H2O. It has been established that the sorption of nickel ions on these precipitates is not accompanied with chemisorption, i.e., the formation of mixed compounds between iron and nickel. Their doping with nickel ions also was not observed. It has been found that the ζ potential of ferrihydrite particles at pH < 5.4 has a positive value, whereas it becomes negative at pH > 5.4. The zero-charge point of the precipitate particles corresponds to pH 5.4.

Crystal and magnetic structure, physical properties (heat capacity, electrical resistivity, magnetic ac -suscepti-bility) of the ordered double manganite PrBaMn2O6 under high external pressure are presented for the first time. Powder neutron diffraction and measurements of physical properties are performed at external pressure up to 5.2 GPa in the temperature interval 50-320 K. Unit cell parameters are determined, the magnetic moment of manganese atoms is calculated with full-profile analysis, linear and volume compression coefficients are esti-mated. According to the neutron diffraction analysis, the material becomes A-type antiferromagnetic insulator at external pressure, while the measurements of physical properties reveal weak signal of the conducting ferro-magnetic state. This discrepancy is explained by a presence of ferromagnetic conducting clusters in the anti -ferromagnetic insulator matrix. The NMR data confirm such an explanation as two contributions from ferromagnetic and antiferromagnetic fractions at ambient pressure have been detected.

Проведен сравнительный анализ состава и структуры свежеосажденных осадков гидроксида железа(III), полученных из раствора сульфата натрия (400 мг/л) при рН 7 и 8 до и после сорбции на них ионов никеля. Методами ИК-, КР- и мессбауэровской спектроскопии, а также рентгенофазового и термического анализов показано, что осадки, полученные из раствора хлорида железа(III) представляют собой двухлинейчатый ферригидрит с брутто-формулой Fe 2 O 3 ⋅3H 2 O. Установлено, что сорбция на этих осадках ионов никеля не сопровождается хемосорбцией, т.е. образованием смешанных соединений между железом и никелем. Не происходит также их легирование ионами никеля. Найдено, что дзета-потенциал частиц осадков ферригидрита при рН < 5.4 имеет положительное значение, а при рН > 5.4 становится отрицательным. Точка нулевого заряда частиц осадков соответствует рН 5.4.

In the development of nanostructured V2O3 materials, the topical issue is to elucidate the factors that affect the temperature of a metal-insulator transition (MIT). In this work, we study the structural, magnetic and electrical properties of V2O3 thin-walled microsphere prepared by spray-pyrolysis (SP). Low-temperature XRD and TEM revealed that SP-microspheres contain the anisotropic (50x20 nm) nanocrystallites with a preferred (001)orientation along the sphere surface and show moderate biaxial compressive stresses. SP-aggregates exhibit a high concentration of intercrystallite boundaries and inner pores, which induce high lattice microstrains. Structural, magnetic and electrical properties showed no evidence of MIT down to 100 K. NMR investigations indicated that antiferromagnetic areas appear at temperatures below 115 K. Comparative studies were performed on V2O3 50 nm nanoparticles prepared by thermolysis using the same parent vanadyl solution. The findings suggest that a high defect concentration and microstrains rather than compressive stresses lead to the suppression of MIT.

Iron(ii) and iron(iii) salts of strong acids form iron glycerolates on heating at 180 °C with glycerol in the presence of an equivalent amount of alkali. Individual iron(iii) glycerolate was obtained for the first time. When Fe3O4 magnetic nanoparticles were heated with glycerol, an iron(iii) glycerolate shell was formed on their surface.

The 61Ni NMR spectra for Ni-based nanoparticles synthesized by the gas-phase method have been obtained. A nanoscale effect has been found in nickel nanoparticles, consisting in a change of the distribution of induced fields when the size of the nanoparticles decreases below a critical size of a single domain. It has been shown that this effect does not depend on the type of shell and is not associated with surface or interface defects. It is assumed that for particles smaller than the critical size, the shift of the hyperfine field is due to the demagnetizing field of single-domain particles. This shift decreases when an inhomogeneous magnetic structure occurs in larger particles.

Removal of heavy metal ions, in particular, divalent nickel ions from natural and wastewater, is of great importance for the environment. Nickel (II) ions are very toxic and provoke many diseases. The purpose of this work was to study the possibility of removing toxic nickel (II) ions from polluted water using an iron (III) chloride (FeCl3) coagulant. It is shown that the removal of nickel ions from aqueous solution by iron (III) hydroxide precipitate formed during the coagulation process at pH 7 and 8 is described with satisfactory accuracy by the classical adsorption isotherms of Freundlich, Langmuir, and Dubinin-Radushkevich. The studies performed with the use of X-ray powder diffraction and thermal analyses, IR, Raman, and Mössbauer spectroscopy have shown that the uptake of nickel ions by iron (III) hydroxide precipitate is due to simple physical adsorption and is not accompanied by the formation of mixed iron and nickel compounds. No alloying of the formed iron (III) hydroxide precipitate with nickel ions takes place either. The formed iron (III) hydroxide precipitate is a two-line ferrihydrite having the gross formula Fe2 O3  × 3H2 O. Its sorption capacity for nickel ions is almost an order of magnitude higher than that of some mineral and carbon sorbents, and at pH 7 and 8, it is 60.5 and 141.9 mg/g, respectively. PRACTITIONER POINTS: Coagulant FeCl3 cleans contaminated solutions from Ni(II) ions. Iron (III) hydroxide precipitated at pH 7 and 8 is a two-line ferrihydrite Fe2 O3  × 3H2 O. Removing of Ni(II) ions is described by classical adsorption isotherms. The most complete removal of Ni(II) ions occurs at pH = 8.

Substantial progress in the area of nanotechnology requires special quality of magnetic nanoparticles. Conventional methods of analysis are not always efficient to the study of nanoparticles. This paper is dedicated to the problem of quantitative analysis of the phase composition of ferromagnetic nanoparticles and the fundamental issue of transition to the single domain magnetic state. A comprehensive study of Fe@C nanoparticles has been carried out, including local Fe-57 NMR and MOssbauer spectroscopy methods. It has been found that the cores of nanoparticles contain phases of alpha-iron, iron carbides, ferromagnetic and paramagnetic phases of iron-carbon FeCx solid solutions. Annealing of the nanoparticles leads to a significant redistribution of the phase composition and leads to an increase in magnetization. Also, a nanoscale effect has been found. It consists in observation of two lines in NMR spectra corresponding to multidomain and single-domain state. The hyperfine fields obtained by NMR and Mossbauer spectroscopy methods are discussed.

The 13 C and 19 F NMR spectra of the original and irradiated polytetrafluoroethylene samples were studied in the range of gamma radiation doses of up to 50 kGy. In this range, the 19 F NMR spectrum width increases linearly with an increase in the absorbed dose. It is concluded that it is possible to monitor technological doses by the NMR method using polytetrafluoroethylene as a detector.

In the paramagnetic phase of cubic antiferromagnet SrMnO2.997 (T-N = 236 K), the spin susceptibility of the localized Mn(t(2g)) electrons exhibits a gapped behavior with d chi(s) (T) >= 0, suggesting the existence of a low-dimensional short-range magnetic order above T-N. The low-frequency fluctuations of the spin correlations of neighboring Mn4+ ions were probed by measuring the spin-lattice relaxation rate T-1(-1) and the echo-decay rate T-2(-1) of O-17 and Sr-87 nuclei up to 420 K. O-17 being involved in an Mn-O-Mn bond, the echo-decay rate T-17(2)-1 probes the fluctuations of the two neighboring S(t(2g)) spins at low frequency, omega <= 10(3) s(-1). It is shown that there exist local changes of the double-exchange interaction, which favor FM correlated pairs of neighboring S(t(2g)) spins in the Mn-O-17-Mn bond. The unusual thermal behavior of T-17(2)-1 (T) indicates low-frequency fluctuations of the short-range magnetic order which may include the change of AF <-> FM spin alignment of neighboring magnetic ions. For Sr-87 nuclei, which probe the spin configuration of eight neighboring Mn ions in the cubic unit cell, T-87(2)-1 has no such anomaly, implying that FM order should be excluded within the cubic unit cell. With both NMR probes, it is deduced that the only magnetic orders which may exist in the cubic unit cells are the following: AF-G [q = pi/a(1, 1, 1)], AF-C [q = pi/a(1, 1, 0)], and AF-A [q = pi/a(0, 0, 1)] so that the slow fluctuating short-range magnetic order is built from these three AF ordered unit cells. Furthermore, we deduce from T-17(1)-1 results that the fluctuating short-range magnetic order, i.e., corresponding to large q, has a high thermal stability in the PM phase of SrMnO2.997.

Field-swept Cu-63,Cu-65 NMR spectra under magnetic fields up to 8.3 T at a constant NMR frequency and temperatures T < 12 K on a single crystalline sample of multiferroic CuFeO2 were measured and analyzed. When the magnetic field is applied along the c axis, a nearly zero internal magnetic field at the Cu site in magnetic ordered state was observed. This is explained by the perfect cancellation of the internal fields produced by the 6 nearest neighbor Fe3+ (S = 5/2) ions, revealing the magnetic structure to be a collinear four-sublattice structure. On the other hand, when the magnetic field is applied along the ab plane, we observed a finite internal field at the Cu sites, which is due to the canting of the Fe moments. Strong change in the NMR signal intensity is observed around 7-8 T, corresponding to the magnetic phase transition from the collinear magnetic to ferroelectric incommensurate states. The ratio of the two magnetic phases significantly depends on the history of the change in the external magnetic field and the temperature of the sample. The details of history dependence of the ratio were discussed.

The 61Ni NMR spectra have been obtained in carbon encapsulated nickel nanoparticles. It has been shown that the cores of the particles consist of metallic nickel with face-centered cubic structure, nickel carbide Ni3C and carbo-nnickel solid solution. The carbon shell of nanoparticles is a highly defective structure and close to an amorphous glassylike carbon.

The spin density distribution of itinerant electrons, n eg , and their effect on pairwise correlations of localized spins S ( t 2 g ) of Mn 4+ ions in cubic Sr 1 − x La x MnO 3 antiferromagnet ( x = 0.02, T N = 230 K, G type magnetic structure) is studied experimentally by nuclear magnetic resonance on 17 O nuclei. The regions with n eg > x , in which the local spin susceptibility of pairs of Mn atoms follows the dependence χ ∼ ( T − Θ) −1 with Θ = 20(5) K, indicating the growth of ferromagnetic spin correlations of neighboring magnetic ions in these domains, are found in the paramagnetic phase. The fraction of Mn-O-Mn bonds ( n eg > x ) increases with the decrease in the temperature. The interpenetrating meshes of Mn-O-Mn bonds with different densities of itinerant e g electrons form an antiferromagnetic metal phase below T N . The role of weak localization effects is discussed as the main origin of the magnetic inhomogeneity of the antiferromagnetic metal phase in Sr 0.98 La 0.02 MnO 3 .

It is shown that 139 La nuclear magnetic resonance data indicate that ferromagnetic regions are formed near La ions in cubic Sr 0.98 La 0.02 MnO 3 manganite. Part of the La ions remain in the antiferromagnetic matrix having a canted structure. The orbital and spin contributions to the shift of the 139 La nuclear magnetic resonance line, as well as the induced hyperfine fields, are determined.