A. P. Nosov

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.

Effect of synthesis on the magnetostrictive properties of CoFe2O4 spinel ferrite

The correlation between methods of synthesis and magnetostrictive properties of ferrite materials is investigated. CoFe2O4 spinel ferrite was synthesized using three techniques: solid-phase reactions, thermal hydrolysis, and sol-gel. The effect of the method of synthesis on the magnetostrictive properties of spinel ferrite is demonstrated.

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.

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.

Crystal and Magnetic State of Multiferroic Composites (x)MFe2O4 + (1-x)BaTiO3, M = Ni, Co

Multiferroic composites of (x)NiFe2O4 + (1-x)BaTiO3 with x = 0.2, 0.3 and 0.4 and (x)CoFe2O4 + (1-x)BaTiO3 with x = 0.2, and 0.4 have been synthesized by mixing NiFe2O4 (CoFe2O4) spinel and BaTiO3 piezoelectric. Distribution of Ni (Co) ions on 8a and 16d positions of spinel lattice (space group Fd-3m) is determined by neutron powder diffraction. Wave vector of magnetic structure of the spinel is k = 0. The dielectric permittivity of the composites was measured for the frequency range 102 – 105 Hz. At low frequencies the dielectric permittivity decreased from ~940 for x = 0.2 to ~360 for 0.4.

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).

Effective generation of the harmonics of magnetic flux in a toroid made of lanthanum manganite

The nonlinear processes related to the magnetization reversal of the two-port with the magnetic core made of the lanthanum manganite doped with lead in the presence of crossed static and RF magnetic fields are studied. The effective harmonic generation is demonstrated at relatively large amplitudes of the RF excitation field and a relatively strong static magnetic field. The experiments are performed at the excitation field frequencies ranging from 5 to 150 kHz and static fields of up to 10 kOe. Both even and odd harmonics (up to the tenth harmonic) are observed.

Penetration of RF Electromagnetic Field through Thin Films of La0.67Sr0.33MnO3 Manganite

Peculiarities of penetration of electromagnetic waves through the bulk and thin film samples of the La0.67Sr0.33MnO3 manganite were investigated for the frequency range from 50 kHz to 20 MHz. Strong variations of penetration coefficient in the applied dc magnetic field were observed both for ferromagnetic and paramagnetic states. Local dynamic magnetic ordering in the paramagnetic temperature range was observed. The experimental data reveal weak dependence of electromagnetic properties on microstructure of the films. The upper frequency limit of the dynamic polaron correlations in the paramagnetic phase was estimated.