E. V. Vladimirova

Glycine-nitrate combustion synthesis of finely dispersed alumina

The possibility of synthesizing different crystalline modifications of alumina Al2O3 by combustion reactions of a mixture of aluminum nitrate with glycine has been analyzed. Aggregated powders of γ-Al2O3 that do not transform into the corundum structure after annealing at a temperature of 1000°C have been prepared. The influence of the synthesis conditions on the specific surface area, bulk density, porosity, and morphology of alumina particles has been investigated.

Synthesis of ferrite spinel NiFe2O4 by thermal hydrolysis and its magnetic properties

A new thermal hydrolysis technique is proposed for synthesis of complex oxide ferrite spinels with the general formula MFe2O4, where M = Ni, Co, Cu, Mn, Zn, etc. The structural, morphological, and magnetic properties of powdered nickel ferrite NiFe2O4 obtained by the proposed technique are investigated.

Synthesis of La1 − xSrxMnO3 + δ manganites by pyrohydrolysis of nitrates

Single-phase finely dispersed perovskite-like manganites La1 − xSrxMnO3 + δ (0 ≤ x ≤ 0.33) with an average particle size of approximately 3μm were synthesized by the pyrohydrolytic method from a stoichiometric mixture of the corresponding metal nitrates at a temperature of 500°C in a water vapor atmosphere. The parameter δ was changed as a result of the subsequent heat treatment. It was established that the manganite La0.67Sr0.33MnO3 + δ synthesized by the pyrohydrolytic method is characterized by a more pronounced change in the magnetoresistance as compared to the manganite that had the same composition but was synthesized according to the conventional ceramic technique.

Penetration of high-frequency electromagnetic field through bulk samples of La1−xSrxMnO3 (0.33 ≤ x ≤ 0.60) manganites

Penetration of radio-frequency electromagnetic field through bulk samples of La1−xSrxMnO3 (0.33 ≤ x ≤ 0.60) manganites has been studied in the frequency range from 20 kHz to 30 MHz at temperatures from 300 to 400 K, which includes the temperature of the magnetic phase transition of some investigated compositions. It has been shown that, in spite of the differences in the static properties, the dynamic properties of the investigated compositions of these manganites are similar; the differences are mainly pronounced at frequencies higher than 1 MHz. In the ferromagnetic range, significant changes in the transmission coefficient have been observed for all compositions upon magnetization. The magnitudes of the initial dynamic magnetic permeability have been estimated. The changes in the transmission coefficient in the ferromagnetic region are mainly caused by changes in the dynamic magnetic permeability rather than by magnetoresistance. It is shown that in the paramagnetic temperature range the magnitude of the dynamic reversible permeability exceeds unity for all compositions, which supports the assumption on the retention of local magnetic ordering.

Stochastic oscillations of magnetic flux in the toroid sample of lead-doped lanthanum manganite

The dynamics of magnetic flux variations in a toroidal sample of the La0.6Pb0.4MnO3 manganite was investigated. Experiments were carried out when the ac magnetic field was applied perpendicular to the dc one. It is shown that under some conditions, several regimes of complex oscillations of magnetic flux can be excited. Evolution of these oscillations as a function of frequency of ac and magnitude of dc magnetic fields was investigated. The signs of existence of the stochastic regime of oscillations were found.

Magnetoresistive Properties of Bulk Polycrystalline Manganites

The paper presents investigations of magnetic transport properties of prospective materials for fabricating magnetic field transducers, namely, bulk polycrystalline manganites La1 – xAxMnO3 (here A = Sr, Ba, or Pb, and 0.15 < x < 0.55) over a temperature range of 260–300 K. The nonlinearity of the magnetoresistance of these materials as a function of magnetic field intensity has been studied at room temperature. Among the materials investigated in the given temperature range, the composition La0.60Sr0.40MnO3 is most susceptible to the applied magnetic field, and the nonlinearity of its characteristic is minimal.

Thermal hydrolysis as a new method of synthesis of the CoFe2O4 spinel ferrite

A new method has been proposed for synthesizing spinel ferrites, i.e., thermal hydrolysis, which makes it possible to obtain a single-phase product of high purity for a short time. A polycrystalline sample of the CoFe2O4 composition has been prepared. The phase composition and morphology of the sample have been investigated and its crystal structure has been refined. The static magnetic characteristics have been measured.

Structure of buffer CeO2 and LaNiO3 layers prepared by method of pulsed laser deposition on textured Ni-Cr-W substrates

The results of an investigation of the structure, composition, and topography of the surface of buffer layers of CeO2, LaNiO3, and CeO2 + LaNiO3 on nonmagnetic textured NiCr9.2W2.4 substrates with a cube texture, which were prepared by pulsed laser deposition, are presented. The substrates with a buffer layer of this composition can be of interest for growing thin films and heterostructures of a wide class of oxide compounds, including superconductors of composition YBa2Cu3O7 − δ (123).

Magnetic-field sensors based on lead-doped lanthanum manganites

The possibility of using lead-doped lanthanum manganites as materials for magnetically sensitive elements of sensors is considered. Measurements of the penetration coefficient of a radio-frequency electromagnetic field as a function of the strength of a stationary magnetic field have been performed. Two variants of using cores made from lanthanum manganites are analyzed. It is shown that cores made from lead-doped lanthanum manganites allow measurements of magnetic fields to be performed in the range 80−4 × 106 A/m. A sensitivity of up to 2.5 × 10−2%/A/m can be achieved for fields of 80−8 × 103 A/m.