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Nanostructured hollow Co3O4 spheres are synthesized by ultrasonic spray pyrolysis. Nanocrystals forming the sphere structure have different sizes and packing density, depending on the synthesis conditions. The samples are studied by X-ray diffraction, scanning electron microscopy, low-temperature nitrogen adsorption, vacuum pycnometry, and Raman and X-ray photoelectron spectroscopies. The field and temperature dependences of magnetization show that the magnetic properties and the Neel temperature of Co3O4 hollow spheres are determined by the size and packing density of nanocrystals.

To create different oxygen nonstoichiometry in oxide samples of NdSr2Mn2O7 + δ, we have used a two-step method of synthesis, which makes it possible to achieve different oxygen nonstoichiometry of the samples. Oxygen nonstoichiometry is formed by two methods: quenching at certain temperatures and annealing at certain values of oxygen partial pressure. The value of oxygen nonstoichiometry is determined by the mass of oxygen emitted from the sample during the decomposition of samples of NdSr2Mn2O7 + δ to simple oxides. We have determined oxygen nonstoichiometry in NdSr2Mn2O7 + δ when recording external parameters such as pressure and temperature. The study of samples of NdSr2Mn2O7 + δ using thermogravimetry and X-rays revealed phase separation—two phases with the same cation composition, having different oxygen content. By example of a sample of NdSr2Mn2O7 + δ tempered from 1000°C and having oxygen nonstoichiometry of +0.09, we have proposed a crystallographic criterion of manifestation of phase separation in Ruddlesden–Popper (R–P) phases—a sharp change in the manganese-oxygen bond lengths. Measurements of the electrical dc resistance in the samples of NdSr2Mn2O7 have been performed in the temperature range of 5–300 K and magnetic fields up to 7 T using the standard 4-probe method. A magnetoresistive effect up to 400% was found in the studied oxides, which is nonlinearly dependent on their oxygen nonstoichiometry.

Magnetic and structural transitions in NdBaMn2−xTixO6 (x = 0, 0.2) samples obtained by the topotactic procedure at 1373 K and lgPO2=−19 atm are studied by low-temperature X-ray diffraction and magnetometry in 1–5 T fields. Undoped double manganite undergoes a reversible ferromagnet—antiferromagnet magnetic phase transition at ТN = 278 K without changing symmetry. The 20 mol.% titanium substitution for manganese causes a decrease in symmetry from the tetragonal space group P4/mmm to the orthorhombic space group Pmmm and a shift of magnetic transitions to lower temperatures. Oxide NdBaMn2O6 demonstrates high values of the magnetocaloric effect in the temperature range 250–315 K.

An amorphous-nanocrystalline Gd2O3 powder with a specific surface area of 155 m2/g has been prepared using pulsed electron beam evaporation in vacuum. The nanopowder consists of 20- to 500-nm agglomerates formed by crystalline nanoparticles (3-12 nm in diameter) connected by amorphous-nanocrystalline strands. At room temperature, the Gd2O3 nanopowder exhibits a paramagnetic behavior. The phase transformations occurring in the powder have been investigated using differential scanning calorimetry and thermogravimetry (40-1400°C). The amorphous phase of the nanopowder is thermally stable up to a temperature of 1080°C. It has been found that the amorphous phase has an inhibitory effect on the temperature of the polymorphic transformation from the cubic phase into the monoclinic phase. It has been revealed that, compared with the microcrystalline powder, the Gd2O3 nanopowder is characterized by a complete quenching of photoluminescence. © 2013 Pleiades Publishing, Ltd.

This work was supported by the Russian Foundation for Basic Research, project no. 10-03-96043-r_Urals_a. Temperature dependencies of density (by the gamma-penetrating method), electrical resistivity (by the contact-less method in rotating magnetic field), and magnetic susceptibility (by the Faraday method) of Sn-Bi alloys with near-eutectic compositions are investigated. The alloy with eutectic composition, Sn -58% (mass) Bi, is shown to differ significantly in the electron structure from hypo- and hypereutectic ones. The melt overheating above the given temperature provides the hysteresis of the properties sensitive to electron structure.

This study was supported by the Russian Foundation for Basic Research (grant no. 07-02-01049). Results are given of an investigation of magnetic susceptibility, electrical resistance, and density of Al62Cu25.5 5Fe(12.5) alloy in the solid and liquid states. It is found that the behavior of the investigated properties at temperatures above the melting point is abnormal. The results are discussed assuming the existence of long-lived (metastable) microregions in the melts.

In this work, we present experimental data of physical properties (viscosity, surface tension, magnetic susceptibility and electroresistivity) studies for Al–R (R = Ce, Pr, Sm, Gd, Dy, Ho, Yb and Y) alloys and first intermetallic compounds from aluminum side, Al 11 R 3 (Al 3 R). All properties were measured during heating up to 2000 K and the following cooling down under helium atmosphere. The main results are: (1) the electronic characteristics of the objects are in good correlation with R positions in the periodic table, but rather lower than for pure elements. The conclusion is that through all investigated temperature range, the rare-earth elements have partly covalent but not only metallic states; (2) all the melts remain strongly microheterogeneous even at high overheatings above liquidus. The existence of associations with Al 2 R type is highly probable here. Some destruction of these associations takes place with increasing temperature above melting point at the composition of Al 2 R compound. However, the transformation into true solution state is somewhere above 1900 K. To check the idea, the thermodynamic modeling of the melts was performed. It was shown that associates with Al 2 R type are stable up to 2000 K.

This work was supported by the Russian Foundation for Basic Research (project no. 11-03-00469-a) and the Ministry of Education and Science of the Russian Federation (state contract no. 16.552.11.7017) using the equipment of the Center of Collective Use "Ural-M" of the Institute of Metallurgy, Ural Branch, Russian Academy of Sciences. The results of measurement of the magnetic susceptibility of the Al86Ni8La6, Al86Ni8Ce6, Al87Ni6Y5, Al86Ni6Co2Gd4Y2, and Al86Ni6Co2Gd4Tb2 alloys in a wide temperature range (T = 290-1900 K) are presented. The effect of the time exposure at different temperatures on the studied property has been investigated. Results have been discussed under the assumption about the existence of microinclusions of Al2REM associates in these alloys.

This work was supported in part by the Special Federal Program NK-255-P/1 and Russian Foundation for Basic Research (grant No. 09-03-90450-Ukr). The magnetic susceptibility of Al2REM (REM = Gd, Dy, and Ho) intermetallic compounds is experimentally investigated by the Faraday method in a wide temperature interval (290-2000 K) in different magnetic fields (0.3-1.3 T). In the crystalline state, the temperature dependences of the susceptibility follow the generalized Curie-Weiss law. In the liquid phase, the magnetic susceptibility of these intermetallic compounds above the melting point increases for all examined samples. The parameters of the electronic structure of the compounds are calculated based on the experimental data. It is established that the effective magnetic moment per rare-earth metal atom is smaller than that characteristic of the free REM+ ion.

This study was supported by the Russian Foundation for Basic Research (grant nos. 07-02-01049, 07-03-96102) and by the Federal Target-Oriented Program (NK-255P/1). The magnetic susceptibility of Al-Co-Ce and Al-Co-Dy amorphous alloys is investigated in a wide range of temperatures (t = 20-1700 A degrees C) and magnetic fields (B = 0.3-1.3 T). A weak gC(B) dependence in the entire temperature range and an anomalous increase in susceptibility beginning above the melting temperature of Al(2)R compound are revealed for all investigated compositions. The experimental data are used to calculate the parameters of the electronic structure of alloys and to estimate the size of super-paramagnetic inclusions. It follows from the experimental data that cobalt atoms are present in these alloys in the nonmagnetic state. It is found that the values of effective magnetic moments on cerium and dysprosium atoms are significantly lower than those for R(3+) ions and independent of the chemical composition of alloys. The results are discussed assuming the existence in melts of microregions formed by quasi-molecules of Al(2)R.

The magnetic susceptibility of Bi100 − x Mn x (x = 5, 7.5, 10, 12.5, 15, 17.5, 20, 25) alloys is experimentally studied by the Faraday method in the temperature range T = 300−1200°C and the magnetic-field range B = 0.6−1.3 T. To calculate the electronic characteristics of the Bi-Mn alloys, the experimental results are approximated by the generalized Curie-Weiss law. The calculated parameters of the electronic structure of the alloys demonstrate that manganese is present in the melt in an ionic state with an effective magnetic moment μeff ≈ 5μB, all Bi-Mn alloys have negative paramagnetic temperatures (which indicate the antiferromagnetic character of the exchange between transition 3d element atoms), and the density of states near the Fermi level n(E F) is low. Therefore, the Fermi level is outside the d band of manganese and its position is controlled by the sp band of bismuth.

This work is partially supported by RFBR (grants 06-08-01290, 07-02-01049). Magnetic susceptibility of dilute Al-Ce and Al-Dy alloys is investigated in wide temperature and field ranges including liquid and amorphous phases. The abnormal behavior of susceptibility above melting point of Al2R compound is discovered. ne concentration curves (chi vs %REM) have oscillating shape similar in solid and liquid states. The existence of Al2R quasimoleculars is highly probable in these alloys and their destruction starts only above melting point of Al2R compound. Magnetic properties of the alloys depend on behavior of such quasimoleculars - creation of chains, nets etc. The estimation of some parameters for such chains and nets is given.