In this paper the electrical and dielectric properties of polycrystalline yttrium iron garnet, obtained by the radiation-thermal sintering technology in a fast electron beam were investigated. Spectra of complex dielectric constant, dielectric loss tangent and conductivity were measured in the frequency range 25 – 1∙106 Hz. For comparison, DC resistance measurements were also performed. The temperature dependences of the above parameters were measured at frequencies of 1 kHz, 100 kHz in the range 25 - 300 °C. It is shown, that conduction activations energy, permittivity, loss tangent and resistance vary significantly from sintering temperature in the range of 1300 to 1450 °C. It is found that with an increase in the sintering temperature to 1450 °C, dielectric properties are the same as samples made by the traditional ceramic technology.

Electrical and dielectric properties of polycrystalline yttrium–iron garnet samples grown by the technology of radiation-thermal sintering in the fast electron beam are considered. In the frequency range from 25 Hz to 1 MHz, the normal complex permittivity, dielectric loss tangent, and ac conductivity spectra are measured. For comparison, in addition to frequency measurements, dc resistivity is measured. The temperature dependences of the above parameters are also measured at frequencies of 1 and 100 kHz in the temperature range of 25–300°C. The activation energies of the ac and dc conduction processes on the Arrhenius coordinates are determined by the temperature dependences of the conductivity. It is shown that as the sintering temperature increases from 1300 to 1450°C, the electrical parameters reach values characteristic of samples grown by conventional ceramic technology.

This article considers structural and technological features, which developers encounter during the creation of microstrip ferrite devices for mm-range microwave equipment. The development results of a 8-mm range microstrip ferrite circulator and isolator are presented in the article.

Samples of polycrystalline yttrium-iron garnet synthesized using radiation-thermal sintering and ceramic processing have been studied by the Mössbauer spectroscopy method. The best decomposition of the Mössbauer spectroscopy spectra of the research objects, which is a simulation of the experimental spectrum with five sextets, has been selected. An additional fifth sextet is caused by Fe3+ ions, which are surrounded by oxygen vacancies leading to distortion of Fe-tetrahedra, which is reflected in an increase in the quadrupole splitting of Fe3+. An increase in the density of s-electrons on Fe ions in distorted tetrahedra has been found, resulting in a decrease in the isomeric chemical shift δ of Fe ions to a value close to the δ value for Fe4+ ions. It has been shown that the optimal crystal structure is realized in Y3Fe5O12 polycrystals when they are sintered for 40–60 min in the temperature range of 1350–1400°C by the radiation-thermal sintering method.

Temperature dependences of the effective magnetic anisotropy field and ferromagnetic resonance linewidth in samples of isotropic and anisotropic hexaferrite SrFe11.2Al0.1Si0.15Ca0.15O19 and anisotropic hexaferrite BaFe10.4Al1.4Si0.15Mn0.1O19, obtained by ceramic technology with wet blanks pressed in the magnetic field of 10 kOe, were studied in the frequency range from 25 to 67 GHz. The studies were carried out at temperatures from 25 to 85°C. The change in the magnetic anisotropy in this temperature range was found to be 9.8 Oe/°C for barium hexaferrite and 4.2 Oe/°C for strontium hexaferrite; the change in the ferromagnetic resonance linewidth was 12.2 Oe/°C for barium hexaferrite and 10–12.3 Oe/°C for strontium hexaferrite.

The Mössbauer spectroscopy (MS) method was used to study polycrystalline iron yttrium garnet (YIG) samples synthesized by radiation thermal sintering (RTS) technology and by standard ceramic technology (CT). The best option for decomposing the MS spectra of the objects of study was selected, which is a model of the experimental spectrum with five sextets. An additional fifth sextet is caused by Fe3 + ions, surrounded by oxygen vacancies which lead to distortion of the Fe tetrahedra which reflected by an increase in the quadrupole splitting of Fe3+. An increase in the density of s-electrons on Fe ions in distorted tetrahedra lead to a decrease in the isomeric chemical shift δ of Fe ions up to a values closed to the δ value for Fe4+ ions. It was shown that the optimal crystalline structure realizes for Y3Fe5O12 polycrystals upon sintering by RTS method in the temperature range of 1350–1400 ° C for a time from 40 to 60 min.

In the work in the frequency range 25 – 67 GHz the temperature changes of the effective magnetic anisotropy field and ferromagnetic resonance linewidth of the samples isotropic and anisotropic hexaferrite SrFe11.2Al0.1Si0.15Ca0.15O19 and anisotropic hexaferrite BaFe10.4Al1.4Si0.15Mn0.1O19 were studied. The samples obtained by ceramic technology with the pressing of the raw blanks in a magnetic field of 10 kOe. The studies were carried out in the temperature range+25 – +85 ºC. It was found that in the specified temperature range, the change in magnetic anisotropy is 9.8 Oe/ºC for barium hexaferrite and 4.2 Oe/ºC for strontium hexaferrite, and the change in ferromagnetic resonance linewidth is 12.2 Oe/ºC for barium hexaferrite and 10 – 12.3 Oe/ºC for strontium hexaferrite.

The work is purely metrological in nature. The developed methods for measuring the effective magnetic anisotropy field HAeff and the line width of ferromagnetic resonance ∆H of magnetically-axis hexagonal ferrites in the working frequency range of the microwave range of electromagnetic waves are presented. Methods allow to determine HAeff in the ranges of 10—23 kOe and 28—40 kOe and ΔН in the range of 0.5÷5 kOe. The first technique (measurement technique in free space in the three-millimeter wavelength range) is implemented in the frequency range 78.33—118.1 GHz. The second technique (the technique using the microstrip transmission line) is implemented in the frequency range from 25 to 67 GHz. Testing of the methods on polycrystalline samples of hexagonal barium and strontium ferrites (both nominal composition and complex ones) with a high degree of magnetic texture, comparison of measurement results with results obtained using standard measurement techniques on spherical samples showed their high accuracy and reliability.

This article discusses the influence of substitution with Al3+ ions on the field of the effective magnetic anisotropy HAeff and the degree of magnetic texture f of anisotropic polycrystalline hexagonal ferrites of barium and strontium. Sample batches are produced by ceramic technology, the texture is formed by compaction in a magnetic field. The preparation of test objects is described in detail. Batches of barium hexaferrites with an ion concentration of Al3+ 0.9, 1.4, 2.5, and 2.6 f.u. and batches of strontium hexaferrites with a concentration of 0.1 f.u. are synthesized. It is demonstrated that the applied procedure makes it possible to obtain barium and strontium hexaferrites with HAeff = 19–35 kE and f = 80–83%. The mentioned values of HAeff and f are sufficient for the production of substrates for microstrip UHV devices of the millimeter wave band. For the first time, it is detected that the degree of the magnetic texture of polycrystalline barium hexaferrites increases with the concentration of Al3+ ions; in addition, a moderate magnetic texture (5.5–5.8%) is observed in isotropic strontium hexaferrites. The experimental results are discussed. The formation mechanism of the magnetic texture in the considered hexaferrites during synthesis is proposed.

In this work the crystal structure and texture of isotropic and anisotropic polycrystalline hexagonal ferrites BaFe 12 O 19 obtained by the method of radiation-thermal sintering (RTS) is studied using X-ray diffraction and X-ray phase analysis. Crude blanks of both isotropic and anisotropic hexaferrites are obtained by the standard method of ceramic technology from the same raw material (Fe 2 O 3 and BaCO 3 of the analytical grade brand) and on the same equipment with the only difference being that the anisotropic blanks were pressed in the magnetic field H = 10 kOe. For sintering raw billets, a linear electron accelerator ILU-6 (electron energy E e = 2.5 MeV) is used (Budker Institute of Nuclear Physics, Siberian Branch, Russian Academy of Sciences). The samples are sintered in air for one hour at 1200, 1250, 1300, and 1350°C. It is shown for the first time that high-quality single-phase isotropic and anisotropic hexaferrites BaFe 12 O 19 can be obtained from raw blanks of a ferritized charge using the RTS technology. The properties of the crystal structure and texture of the obtained objects of the research are described. It is established for the first time that the dependence of the pref.orient.o1 predominant orientation of the crystal texture parameter on the degree of the magnetic texture f in polycrystalline hexagonal barium ferrites of type M is described by the expression pref.orient.o1 = –0.005 f + 0.6886.

Исследование особенностей получения методом шликерного литья пленок гексаферритов для подложек сверхминиатюрных микрополосковых ферритовых развязывающих приборов коротковолновой части миллиметрового диапазона длин волн

Using polyelectrolytes, ecologically safe film elements from hexaferrites have been designed for the first time with water slurry casting instead of existing processes with the use of organic solvent binders. The use of polyelectrolyte substances as binders has made it possible to reduce the energy consumption of drying by 20–30% during the process of film casting.

Исследовано влияние лимонной кислоты и изопропилового спирта на процессы мокрого измельчения смеси исходных ферритобразующих компонентов и синтезированной ферритовой шихты. Установлено, что введение добавок при мокром измельчении позволяет заметно снизить температуры синтеза феррита и спекания сырых заготовок, повысить уровень магнитных свойств постоянных магнитов из бариевых ферритов путем формирования плотной мелкозернистой структуры. Увеличение активности порошков объясняется формированием активных гелеобразных прослоек на поверхности частиц в процессе мокрого измельчения.

The effect of citric acid and isopropyl alcohol on the wet grinding of the mixture of initial ferriteforming components and synthesized ferrite charge has been analyzed. It has been established that the introduction of admixtures during wet grinding makes it possible to substantially reduce the ferrite synthesis temperature and the sintering temperature of green billets and to improve the magnetic properties of permanent magnets made of barium ferrites by the formation of a dense, fine-grained structure. The increase in the activity of powders is explained by the formation of active jelly-like interlayers on the surfaces of particles during wet grinding.

Study the influence of citric acid and isopropyl alcohol on processes of wet grinding mixture of starting ferrite constituting components and synthesized ferrite charge. Found that the introduction of additives during wet grinding allows to significantly reduce the temperature of synthesis and sintering ferrite raw blanks. Increased activity of powders is explained by the formation of active the gelled layers on the surface of particles in the process of wet grinding.

The effects of the base composition and dopants on the saturation magnetization and coercivity of hexaferrites BaAl x Fe 12– x O 19 , SrAl x Fe 12– x O 19 , BaGa x Fe 12– x O 19 , SrGa x Fe 12– x O 19 , BaSc x Fe 12– x O 19 and SrSc x Fe 12– x O 19 have been studied. Isomorphic substitutions of Al 2 O 3 , Ga 2 O 3 , and Sc 2 O 3 for Fe 2 O 3 in barium and strontium ferrites are found to increase coercivity due to increasing crystallographic anisotropy constant and to reduce the saturation magnetization value. Processes controlling microstructure formation, specifically recrystallization processes, are shown to have a noticeable effect on the level of properties of the ferrites under study with the use of dopants. The most efficient dopants are boron, calcium, and silicon oxides, which provide the formation of relatively fine-grained structures. The increased coercivity upon doping with these dopants is also due to the formation of grain-boundary interlayers of a nonmagnetic glassy phase and the associated efficient retardation of moving domain walls.

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 +2 Me +4 ) x Me y + 3 Fe 12– x – y O 19 hexagonal ferrites with thermally stable anisotropy field and coercive force are presented. It is shown that doping with metal vapors of Me +2 Me +4 = Ni +2 Ti +4 , Ni +2 Ge +4 , Ni +2 Cu +2 Ge +4 , Me +3 = Al +3 , Cr +3 allows improvement in the reproducibility of the properties and the thermal stability of barium hexaferrite.