Microstructure and magnetic properties of Sn-substituted MnZn ferrites

Sn-substituted MnZn ferrites were prepared by conventional oxide ceramic process. The influences of Sn substitution on microstructure and magnetic properties of MnZn ferrites were investigated. The results indicated that with increase of Sn substitute concentration, the diffraction peaks shifted slightly towards the lower angles and the lattice parameter (a) increased. And at room temperature, the bulk density (d_m), initial permeability (μ_i), saturation magnetic induction (B_s) and electrical resistivity (ρ) of Sn-substituted MnZn ferrites all increased initially and then decreased with the further increase of Sn substitute concentration, while the power losses decreased first and then increased subsequently. Meanwhile, the temperature of secondary maximum peak of μ_i-T curve and the minimum losses moved to lower temperature while the Sn substitute concentration increased. When the content of Sn substitution was 0.3 mol%, at room temperature, the initial permeability, saturation magnetic induction, density and electrical resistivity reached their maxima, while the hysteresis loss (P_h), eddy current loss (P_e) and total losses (P_cv) achieved their minima. The P_h∼T and μ_i-T curves varied contrarily, and due to the contribution of extra eddy current loss (P_e,exc) that was proportional to P_h, the P_e-T curve did not agree with its classical expression. Finally, MnZn ferrite substituted with 0.3 mol% SnO₂ shows the highest initial permeability (3894) and lowest losses (303 kW/m³) at room temperature.     

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.     

Field dependence of magnetic susceptibility of yttrium-gadolinium ferrites

Russian Physics Journal -     

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.     

Effects of Ta2O5 addition on the microstructure and temperature dependence of magnetic properties of MnZn ferrites

MnZn ferrites with the chemical formula Mn_0.68Zn_0.25Fe_2.07O₄ have been prepared by the conventional ceramic technique. Toroidal cores were sintered at 1350 °C for 4 h in N₂/O₂ atmosphere with 4% oxygen. Then the influence of Ta₂O₅ addition on the microstructure and temperature dependence of magnetic properties of MnZn ferrites was investigated by characterizing the fracture surface micrograph and measuring the magnetic properties over a temperature ranging from 25 to 120 °C. The results show that, when the Ta₂O₅ concentration is not more than 0.04wt%, the grain size has a slight increase with the increase of Ta₂O₅ concentration, the temperature of secondary maximum peak in the curve of initial permeability versus temperature and the lowest power loss shift to lower temperature. However, excessive Ta₂O₅ concentration (>0.04wt%) results in the exaggerated grain growth and porosity increase, which make the initial permeability and saturation magnetic flux density decrease and the power loss increase at room temperature. Furthermore, the temperature of secondary maximum peak in the curve of initial permeability versus temperature and the lowest power loss shift to about 100 °C.     

Analysis of the microwave magnetic permeability spectra of ferrites with hexagonal structure

This paper presents the results of theoretical and experimental investigations of the microwave magnetic permeability spectra of polycrystalline ferrites with hexagonal crystal structure. It is shown that the observed nonmonotone frequency dependence of the permeability is due to the features of the natural ferromagnetic resonance in the presence of a domain structure. The calculations of the contribution of the rotation of the magnetization vector to the permeability performed in the approximation of independent grains adequately describe experimental data. __________ Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 9, pp. 119–124, September, 2006.     

Effects of microstructure on the temperature dependence of relative initial permeability of NiCuZn ferrites

In the present work, ferrites with compositions of (Ni_0.27Zn_0.64Cu_x)Fe_1.98O₄ (x=0.1, 0.2) were prepared by conventional ceramic methods. The relationship between the microstructure and the temperature dependence of relative initial permeability was investigated. It was found that intergranular pores in the ferrites generate large demagnetizing fields, reducing the temperature dependence of the effective anisotropy field H_eff, and decreasing the temperature dependence of the relative initial permeability accordingly. However, intragranular pores pin the movement of domain walls. Compared with the permeability induced by domain wall motion, the permeability that resulted from the spin rotation is more sensitive to temperature. As a result, the relative initial permeability of ferrites becomes more sensitive to temperature with increasing micropores within grains.     

Influence of Sn-substitution on temperature dependence and magnetic disaccommodation of manganese-zinc ferrites

In this paper, the effects of Sn-substitution on temperature dependence and magnetic disaccommodation of manganese-zinc ferrites were investigated. Toroidal cores were prepared by the conventional ceramic process and sintered at 1360 °C for 4 h in atmosphere controlled by using the equation for equilibrium oxygen partial pressure. The experimental results show that the substitution of Sn⁴⁺ in manganese-zinc ferrites can influence the thermal stability and disaccommodation remarkably. Secondly, the temperature dependence of the initial permeability μ_i and disaccommodation of Sn-substitution manganese-zinc ferrites have an internal relationship. The experimental results are explained and compared with those of Ti-substitution manganese-zinc ferrite.     

Laser damage in ferrites of MnZn spinels and other possible interactions

Pulsed laser damage of ferrites of MnZn spinels was studied. Some of the samples were treated by nuclear gamma radiation and α particles and then exposed to laser beams in different working conditions. The sample and damage quality was evaluated on the basis of X-ray, optical and SEM microscopy and micro-hardness experiments. The characteristic brittleness after nuclear gamma irradiation of ferrites and other materials was confirmed in the cases of interactions with laser beams. Characteristic cases of material cracks with CO₂ laser were found.     

Temperature dependence of the first constant for the crystallographic magnetic anisotropy for polycrystalline lithium-aluminum ferrites

Measurements by approach to saturation are reported for specimens of composition witha = 0; 0. 2; 0. 4; 0. 5; 0. 6, over the range 170 ° to 530 ° K. Modulated fields are used to examine the approach to saturation.     

Temperature dependence of spontaneous magnetization of spinel ferrites with a frustrated magnetic structure

The spontaneous magnetization of the Ni_0.4Fe_0.6[Ni_0.6Cr_1.4]O₄, Cu_0.4Fe_0.6[Ni_0.6Cr_1.4]O₄, and Zn_0.4Fe_0.6[Ni_0.6Cr_1.4]O₄ samples has been investigated. Based on the results obtained, it is concluded that the anomalous temperature dependences of spontaneous magnetization stem from the presence of a frustrated magnetic structure in at least one of the sublattices.     

The effect of sintering time and temperature on the electrical properties of MnZn ferrites

Polycrystalline samples of Zn_0.37Mn_0.58Fe_2.05O₄ have been prepared by the solid state reaction method. The structural characterization of the samples indicated that 1523 K is the most proper temperature for obtaining a single phase spinel structure. The DC electrical conductivity measurement was carried out by a two-probe method. Temperature dependent of DC electrical conductivity increases with increase in temperature ensuring the semiconductor nature of the samples. The drift mobility was estimated and found to be temperature dependant. The electrical conduction mechanism in these samples change from hopping, in the low temperature range, to polaron hopping in the high temperature range. The portion of energy Δε anticipated in hopping was determined. It decreases with increasing the sintering time and temperature. PACS 70; 71.20.Nr; 75.50.Gg     

Stress dependence of the magnetic properties of amorphous Co-Fe-Si-B alloys

For the amorphous alloys Co_75−xFe_xSi₁₅B₁₀ (x = 0, 2, 4, 4.6) and Co₇₅Si₅B₂₀, we have studied the stress depe ndence of the coercive field, the initial susceptibility, the effective anisotropy, and the reduced remanence. The experimental results are in good agreement with a model due to Vázquez, Fernengel and Kronmüller. From our measurements, we obtain the magnetostriction, as well as information about quenched-in stresses and anisotropy mechanisms in these materials.     

Monocrystalline high-saturation magnetization ferrites for video recording head application: II. MnZn ferrites with large FeII contents

Monocrystalline Fe^II-rich MnZn ferrites are considered as candidate materials for video recording heads, to be used for both writing and reading when magnetic tapes of high coercivity are applied. It is examined how saturation magnetization and magnetostriction constants vary with chemical composition within relevant areas of the ternary composition diagram MnFe₂O₄-ZnFe₂O₄-Fe^IIO₄. From the results and data known for the magnetocrystalline anisotropy a composition is selected which offers a fairly good compromise between high-saturation magnetization and suitable soft magnetic properties. A study is presented of magnetic and electrical properties of monocrystals of this composition, relevant to their use as video recording head materials. The present paper is the second in a series of three dealing with Fe^II-rich ferrites for video recording head application.     

Monocrystalline high-saturation magnetization ferrites for video recording head application: I. Zn ferrous ferrites

Monocrystalline Zn ferrous ferrites Zn_xFe_3-xO₄, with x ? 0.4, are considered as candidate materials for video recording heads, to be used for writing on magnetic tapes of high coercivity. The saturation magnetization of these ferrites can be as high as 0.7 T at 20°C. We show that because of the small dimensions of modern video recording heads, the relatively high electrical conductivity of the Zn ferrous ferrites is not an obstacle to their use at video frequencies. Measurements are reported of magnetic and electrical parameters relevant to recording head application. It is shown that some of the magnetic parameters can be influenced positively by Co^II additions. The present paper is the first of a series of three dealing with Fe^II-rich ferrites for video recording head application.     

Anomalous permeability in Polder-Smit region of ferrites

A study of the magneto-microwave Kerr effect on two samples of ferrites lying in the Polder-Smit region gives a negative value of μ', the real part of the transverse diagonal term of permeability tensor. There is a negative peak for μ' at a d.c. magnetization approximately equal to $\text{3}\text{4}$ of the saturation magnetization.