Measuring the 9-component magnetic permeability tensor of ferrites

The magnetic permeability tensor of ferrite monocrystals can, in the general case, be represented as consisting of nine components [1]. In [2] the 6-component magnetic permeability tensor was obtained for a triaxial ferrite monocrystal with low magnetic anisotropy energy magnetized by a constant field in the crystallographic plane (110). In the general case of magnetization in an arbitrary crystallographic direction the tensor becomes a 9-component tensor [3]. In the context of the increasing application of ferrite monocrystals in microwave engineering the question of measuring such a tensor is of current scientific and practical interest. In the present article we propose a method for measuring the 9-component tensor for ferrite materials at microwave frequencies.     

Effect of porosity on the magnetic behaviour of nickel ferrites

The magnetic behaviour of polycrystalline materials is closely related to their specific manufacturing process. Beside composition, the various factors that affect this behaviour and cause the particular microstructure of these materials include non-magnetic inclusions, grain size, pressing, temperature, sintering time, and cooling rate. A study has been done of magnetization curves and static hysteresis loops in a set of polycrystalline nickel ferrites. The experimental results were fitted by a second-order rational function, which easily allowed us to calculate their characteristic parameters, and analyze them according to the non-magnetic inclusions model.     

Effect of quenching temperature on the components of the permeability tensor and the complex dielectric constant of microwave magnesium ferrites

We report an investigation of the effect of the quenching temperature (from 900 °C, 700 °C, and for self-cooling) on the components of the permeability tensor and on the complex dielectric constant * of magnesium-aluminum, magnesium-chromium and magnesium-manganese, ferrites of fixed composition. The measuring apparatus and measurement procedure are described and an estimate of the errors is given. It is shown that due to quenching the gyrotropic properties of the ferrites are increased ( falls and _a increases), while the dielectric constant is unchanged. Quenching leads to an increase in the magnetic and dielectric losses.Translated from Izvestiya VUZ. Fizika, Vol. 11, No. 11, pp. 41–47, November, 1968.     

The relation between the inner demagnetizing factor of manganese magnesium ferrites and their porosity and permeability

It is shown that the simple relation of direct proportionality between the inner demagnetizing factor and the relative volume of the pores is not sufficient to explain the experimental data obtained on a system of manganese magnesium ferrites. An equation is derived in which the inner demagnetizing factor is directly proportional to the ratio of the relative volume of the pores to the permeability of the sample. The values calculated according to this equation agree well with the experimental results.

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Effect of pores and nonmagnetic inclusions on ferromagnetic resonance in polycrystalline ferrites

In this paper an account is given of the experimental results concerning the effect of pores and nonmagnetic inclusions on the ferromagnetic resonance line parameters in polycrystalline ferrites. Calculations of linewidth, resonance field, and first moment are compared with experiment in a wide range of porosity. The effect of porosity on the frequency dependence of the linewidth is discussed.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 2, pp. 112–115, February, 1982.     

Equation of the ferromagnetic resonance line in polycrystalline ferrites

Ferromagnetic resonance in polycrystalline ferrites is considered in the framework of the independent-grain model. It is shown that the ferromagnetic resonance absorption line can be obtained analytically from its moments. When a limited number of moments of the line are known explicitly, the method of Pearson curves is used to obtain the equation of the line. The obtained expression is analyzed and the resonance field and absorption line width deduced from the equation are compared with results obtained earlier.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 3, pp. 19–23, March, 1981.     

Dependence of the ferromagnetic-resonance parameters of polycrystalline ferrites on uniaxial elastic stress

Methods developed for taking into account the effect of magnetic crystallographic anisotropy on ferromagnetic resonance in polycrystalline ferrites are used to calculate the dependence of the line width of resonant ferromagnetic absorption and the magnitude of the resonant field of polycrystalline ferrites on uniaxial elastic stress.Translated from Izvestiya Vysshikh Uchetanykh Zavedenii Fizika, No. 10, pp. 49–55, October, 1970.     

Effect of grain size on TL yield of polycrystalline BaS: Bi phosphors

Effect of grain size on thermoluminescence (TL) of BaS: Bi (0.36% by wt.) phosphors was studied by X-irradiation at RT (30° C). It is observed that the the intensity of phosphorescence and TL output decrease with the decrease of the grain size of the powders, which has been attributed to the loss of incident excitation energy due to scattering.     

Effect of grain sizes on the metal-semiconductor phase transition in vanadium dioxide polycrystalline thin films

Experimental data on the effect of grain sizes on the shape and width of the hysteresis loop characterizing a metal-semiconductor phase transition in vanadium dioxide films are analyzed in terms of the classical theory of nucleation. It is shown that the factors responsible for the changes in the shape and width of the hysteresis loop with variations in the size of the grains making up a film are associated with the heterogeneous character of nucleation of a new phase, on the one hand, and with the elastic stresses arising in the phase transition, on the other.     

Stress dependence of the magnetic permeability of MnZn ferrous ferrites

In monocrystalline MnZn ferrous ferrites the magnetic permeability μ as a function of temperature T has been observed to show a striking dependence on applied stress. Stresses cause the μ(T) curve to cant around a point near its maximum arising from compensation of the magnetocrystalline anisotropy due to the ferrous ions. By grinding the surface of a monocrystalline toroid, a tensile stress was exerted on the interior of the specimen. The canting of the μ(T) curve observed when the damaged surface layer was removed step by step was employed to study the underlying physical mechanism. In the case of polycrystalline materials the maximum of μ(T) is usually strongly suppressed. Nevertheless, it proved possible to investigate the dependence of μ(T) on applied stress in a polycrystalline MnZn ferrous ferrite pot core.     

Effect of grain boundary on electrical properties of polycrystalline lanthanum nickel oxide thin films

In the present work, lanthanum nickel oxide (LNO) thin films were prepared by the sol-gel method. Microstructures of the films were tailored by changing sol concentration so as to investigate the effect of grain boundary on the transport properties of electrons in the polycrystalline LNO films. Based on the temperature dependence of the resistivity and the magnetic field dependence of the magnetoresistance (MR) at various temperatures, the factors that dominate the transport behavior in the polycrystalline LNO films were explored in terms of weak localization and strong localization. The results show that the grain boundary has a significant influence on the transport behavior of the electrons in LNO films at a low-temperature region, which can be captured by a variable-range hopping (VRH) model. The increase of metal–insulator (M–I) transition temperature is ascribed to Anderson localization in grain boundary. At a high-temperature region, electron–electron scattering and electron–phonon scattering predominates in the films. In this case, the existence of more grain boundary shows a minor effect on the transport behavior of the electrons but elevates the residual resistivity of the films.     

Tailoring the temperature characteristics of the magnetic permeability of NiZn ferrites

The effect of cobalt addition on the temperature characteristics of the magnetic permeability of NiZn ferrites was studied and a comparison to the respective behaviour of cobalt in NiCuZn ferrites was examined. Cobalt-doped NiZn and NiCuZn ferrites were manufactured by the ceramic route and sintered under various atmosphere profiles. The chemical and morphological characteristics were evaluated by X-ray diffraction (XRD), scanning electron microscopy (SEM) and thermogravimetric analysis (TGA). The evaluation of the magnetic performance of the sintered ferrites showed that N₂-rich atmosphere profiles during the top temperature and cooling time of the sintering process favour the temperature stability of the permeability in the case of NiZn ferrites, while preserving the losses at low levels. Two mechanisms that take place at the same time are proposed: the change of the Fe²⁺/Fe³⁺ ratio due to the reduction-promoting atmosphere of N₂ in combination with an increase in magnetocrystalline anisotropy and magnetostriction due to the presence of Co²⁺ suggest a useful method to tailor the temperature factor α_F of NiZn ferrites. However, the method cannot be applied in NiCuZn ferrites, as the reduction Cu²⁺-Cu⁺ taking place under N₂-rich atmospheres enhances secondary re-crystallization phenomena, causing a dramatic increase in losses.     

Dependence of photoconductivity on the crystallite orientations and porosity of polycrystalline ZnO films

Hexagonal ZnO films deposited on quartz glass, sapphire and glass substrates by sol–gel coating are found to be randomly oriented; maximum randomness is found in the film on quartz glass substrate. All the films are ultra-violet (UV) sensitive at around 360 nm sensitivity being maximum for the film with maximum randomness in the crystallite orientations. The film on quartz showed the lowest dark current and maximum photoresponse, which is related to the lowering of the barrier heights, introduced by the adsorbed oxygen at the grain boundaries. Faster decay in photocurrent is observed for the film deposited on glass, which is attributed due to the smaller crystallite sizes with porous microstructure of the film. PACS 73.61.Ga; 68.55.Jk; 73.50.Pz     

Influence of inhomogeneous exchange interaction on the moments of the ferromagnetic resonance lines in polycrystalline ferrites

From the viewpoint of the spin-wave approach to the theory of ferromagnetic resonance, the first four moments of the absorption line are calculated in this paper. It is shown that in addition to the magnetic dipole-dipole interaction, the inhomogeneous exchange interaction which has been neglected in previous papers exerts substantial influence on the asymmetry and peakedness of the ferromagnetic resonance line.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 7, pp. 75–78, July, 1979.     

On the problem of the internal effective field for ferromagnetic resonance of polycrystalline ferrites

A study was made of the ferromagnetic resonance of MnZn ferrite in the temperature region –124 °to +182 °Cin the 3 cmband. The additional internal effective field and its temperature dependence was determined. A comparison with the results of measurements of the initial permeability carried out at the same time pointed to the close relationship between magnetocrystalline anisotropy and the additional field or apparent value of the Landé factor g.