V.G. Kostishyn

Influence of technological factors and chemical composition on the thermal stability and electromagnetic properties of M-type hexaferrites

The possibility of increasing the coercive force of barium hexaferrite by the isomorphous substitution of iron oxide with alumina, gallium and scandium oxides, and by impurity doping is shown. The results of the synthesis and study of new a (Me+2Me+4)xMey + 3Fe12–x–yO19 hexagonal ferrites with thermally stable anisotropy field and coercive force are presented. It is shown that doping with metal vapors of Me+2Me+4 = Ni+2Ti+4, Ni+2Ge+4, Ni+2Cu+2Ge+4, Me+3 = Al+3, Cr+3 allows improvement in the reproducibility of the properties and the thermal stability of barium hexaferrite.

Tunable microwave electric polarization in magnetostrictive microwires

In this work, the induced electric dipole moment of ferromagnetic microwires dependent on the wire magnetic structure is investigated with the aim of sensing applications. The wire behaves as micro antenna exhibiting a resonance at half wavelength condition. At the vicinity of the resonance the wire polarization is sensitive to all the losses including magnetic losses. The transfer mechanism is based on the magnetoimpedance effect (MI) which requires a specific magnetic structure of a helical type. We demonstrate that scattering from a ferromagnetic microwire showing large MI effect at microwaves can be modulated with a low frequency magnetic field and the amplitude of this modulation near the antenna resonance can sensitively change in the presence of the external stimuli such as a dc magnetic field. The modelling is based on solving the scattering problem from a cylindrical wire with the impedance boundary conditions. The modelling results agree well with the experimental data.

Study of the features of the magnetic and crystal structures of the BaFe12-Х ALXO19 AND BaFe12-Х GaXO19 substituted hexagonal ferrites

The mechanism of formation of polycrystalline hexagonal barium ferrite with diamagnetic substitution with Al and Ga ions is considered. The localization of the dopants (Al and Ga) in hexagonal and spinel blocks is shown. It is found that the main Al – Fe and Ga – Fe substitutions occur in the 12k sublattice. The substitutions break the Fe–O–Fe exchange couples of the 12k sublattice with other sublattices, which leads to the emergence of non-equivalent positions of Fe3+ions, on the basis of which in the Mossbauer spectra with isomorphic aluminum, 7 sextets are identified and with isomorphic gallium – 6. This leads to a decrease in the magnetic parameters of ferrites, such as specific and residual magnetization, Curie temperature. It is shown that aluminum (x=2.1) entry increases the coercive force, magnetic hardness of the hexagonal ferrite, and gallium (x=0.6) entry lowers the coercive force and magnetic hardness. The angles θ between the magnetic moment and the γ-radiation direction in isotropic substituted hexagonal ferrite polycrystals and foil are determined.

Obtaining Hexagonal Ferrites for Substrates Microstrip Microwave Devices of mm-Range of LTCC-technology

In the work by the method low temperature co-fired ceramics (LTCC) obtained samples of isotropic and anisotropic polycrystalline hexaferrite BaFe12O19 and SrFe12O19. Using in the LTCC-technology the pressing operation for samples (tablets) in a magnetic field produces anisotropic hexaferrites, pressing without a magnetic field isotropic hexaferrites. Application in the LTCC-technology molding process tape produces exclusively isotropic samples.

Effect of Corona Treatment on Magnetic Properties of Nanoscaled Multiferroic Films BiFeO3, (BiLa)FeO3 and (BiNd)FeO3

Multiferroic films of BiFeO3, (BiLa)FeO3 and (BiNd)FeO3 with various concentration of ions of Bi, La and Nd in dodecahedral sublattice utilising were fabricated on monocrystalline substrates of (001) SrTiO3, (100) MgO and (100) Al2O3 by a number of technological methods: rf sputtering, vacuum laser ablation and metal-organic chemical vapor deposition (MOCVD). The film thickness varied in the range of 30-300 nm. The magnetic and magnetoelectric properties of the obtained films were investigated. The saturation magnetization of BiFeO3 was about 9 emu/cm3 which is typical of strained films of this composition. Doping BiFeO3 films by rear earth ions La (Nd) increases both the magnetisation saturation and Neel temperature, as well as magnetoelectric effects, which is explained by increase in magnetic crystal anisotropy and suppression of spatially modulated magnetic structure. It was demonstrated that the corona discharge treatment resulted in a substantial growth of the magnetisation saturation up to 35% whereas the changes in the Neel temperature were not noticible. This is explained by the induced electret state and giant magnetoelectric effect.

Synthesis of hexagonal BaFe12O19 and SrFe12O19 ferrite ceramics with Multiferroic Properties

The possibility of obtaining by ceramic technology barium and strontium hexagonal ferrites of the M type with multiferroic properties is considered. For the first time, samples of BaFe12O19 and BaFe12O19 with intense multiferroic properties at room temperature are obtained using a modified ceramic technology (particularly clean feedstock, B2O3 additives, sintering in an oxygen atmosphere). A comparison of the characteristics of the obtained multiferroic samples with the characteristics of the classical high-temperature multiferroic BiFeO3 as well as with the characteristics of ferrite ceramics BaFe12O19 and SrFe12O19 obtained by the technology of polymer precursors is performed. A mechanism to explain the properties of multiferroic hexagonal ferrite ceramic samples is proposed; the important practical significance of the results is noted.

Distribution of magnetization in microwire magnetoimpedance elements

An important prerequisite for successfully developing highly sensitive magnetic field sensors based on amorphous ferromagnetic microwires is to study the conditions of excitation and the effect external magnetic fields on magnetoimpedance in amorphous ferromagnetic microwires. The distribution of magnetization is considered a function of the magnetic properties of a wire material, the bias current, and the strength and orientation of the external magnetic field.