Manganese Zinc Ferrite Research Articles

Improved domain-wall model of static hysteresisfor power ferrites

An improved domain-wall surface function R(m) is suggested for the static domain-wall hysteresis model proposed by Basso and Bertotti to better characterise the very soft saturation behaviour of manganese-zinc (MnZn) ferrites. The improved model is verified against experimental data for the major and minor hysteresis loops of three commercial MnZn ferrites.

磁場配向で作製したＭｎ‐Ｚｎフェライトの磁気特性

Acicular manganese zinc ferrite fine particles were made from the as raw materials of acicular α-FeOOH, Mn(C5H7O2)3, and Zn(C5H7O2)2. These fine particles were oriented with the long axis in parallel to the magnetic flux direction by a magnetic field of 7 kOe. The fine particles were then formed into thin, multi-layered toroidal cores. The green bodies were sintered at 1200°C for 6 hours in air, then cooled in a nitrogen atmosphere. The crystals of sintered manganese zinc ferrites were strongly oriented to the direction of the (110) plane of the spinel; this plane was formed along the upper plane of toroidal cores. The crystal growth behavior was similar to that of a manganese zinc ferrite single crystal of the (110) plane. The initial permeability of crystal-oriented manganese zinc ferrites was 2120. The sample exhibited good high-frequency magnetic properties.

磁性材料 小粒径針状α‐ＦｅＯＯＨから作製した配向性Ｍｎ‐Ｚｎフェライトの磁気特性

Acicular manganese zinc ferrite fine particles were made from small acicular α-FeOOH, Mn(C5H7O2)3, and Zn(C5H7O2)2. The long axis of these fine particles was oriented in parallel to the external magnetic field of 557kA/m, and then formed into multi-layered toroidal core. The green compact was sintered at 1200°C for 6 hours in air, and then cooled in a nitrogen atmosphere. The relative bulk density of the sintering body was improved from 87.0% to 90.2%. Crystallites consisted of the {110} plane were aligned along the upper plane of toroidal core of crystal-oriented manganese zinc ferrite. The initial permeability of crystal-oriented manganese zinc ferrite was 2240 at 0.1 MHz. The sample exhibited excellent high frequency magnetic properties.

Effect of sintering enclosures and sintering parameters on the magnetic properties of a high permeability manganese-zinc ferrite

Manganese-zinc ferrite (Mn/sub 0.52/Zn/sub 0.41/Fe/sub 2.07/O/sub 4/) has been prepared by the mixed-oxide route. Specimens were in the form of toroids, pressed in the green state to 11.9 mm outside diameter and 5.9 mm inside diameter. To assess the effect of zinc loss, a variety of circular local sintering enclosures were employed. All specimens were initially sintered in air at 1390/spl deg/C for times of 7.5-16 h. After cooling to 1200/spl deg/C they were held for 4 h in atmospheres containing 0.0125-0.05% oxygen. Sintered products were single-phase, with density greater than to 95% theoretical and a grain size of about 20 /spl mu/m. Use of a partial sintering enclosure led to a 45% increase in initial permeability /spl mu//sub i/, but use of a full enclosure led to a reduction in /spl mu//sub i/. Firing the samples at 1200/spl deg/C in an atmosphere containing initial permeability was maximized (about 10200) over a wide range of temperatures 25-90/spl deg/C. The eddy current losses in such samples were twice as high as for samples sintered in an oxygen atmosphere containing 0.05% oxygen.

Direct current-induced bonding between single- and polycrystalline manganese-zinc ferrites

The application potential of dc electric fields to promote and optimize the ferrite bonding between single- and polycrystalline manganese-zinc ferrite was investigated. The ferrite bonding process was accelerated under the application of a dc electric field. The degree of bonding increased as the bonding time and bonding temperature were increased. It was also found that the direction of an applied current from the poly- to single-crystalline ferrite regions enhances bonding.

Ceramic innovations in the 20th century

Ceramic innovations in the 20th century

The role of the dispersed-phase remnant magnetization on the redispersibility of magnetorheological fluids

The influence of the remnant magnetization of the soft magnetic particulates, used as a dispersed phase, on the redispersibility of magnetorheological (MR) fluids is discussed. Calculations of the magnetic interaction energy showed that for 33-vol% MR fluids based on particles of iron (∼6 μm), manganese zinc ferrite (∼2.3 μm), and nickel zinc ferrite (∼2.1 μm), the ratios of the magnetic interaction energy to the thermal energy were 161,000, 6400, and 3900, respectively. These calculations showed that even the seemingly small levels of remnant magnetization, associated with particulates employed in MR fluids, introduced significant dipole–dipole interparticle interactions. It is proposed that this interaction causes most MR fluids to show a tendency for “cake formation,” which makes it difficult to redisperse these fluids. Our modeling presented here also suggests practical strategies to enhance the redispersibility of MR fluids.

NMR investigations of ion distribution in real structure of manganese-zinc ferrites

Using the nuclear magnetic resonance, X-ray and electromagnetic methods we investigated structure and properties of the single- and polycrystalline manganous and manganese-zinc ferrites: MnFe2O4, Mn0.8Zn0.2Fe2O4, Mn0.6−xCuxZn0.3Fe2.1O4 (0 ≤x ≤ 0.3). The real structure of the manganous and manganese-zinc ferrites is found to contain simultaneously vacancies in cationic and anionic sublattices. The analysis of the NMR spectra of55Mn,57Fe,63,65Cu and67Zn ions allowed us to find the magnetic and valence states of all ions and their distribution in the real spinel structure. It was shown that the Fe3+ paramagnetic ions, Zn2+ diamagnetic ions and cationic vacancies in tetrapositions are distributed statistically. The Mn3+ and Cu2+ Jahn-Teller ions and presumably Fe2+ in octahedral positions are distributed nonstatistically forming cluster-type mesoscopic inhomogeneities. The correlation between distribution of ions and vacancies in the real structure of manganese-zinc ferrites and their functional electromagnetic properties was found.

シナジー磁石と磁性材料 針状α‐ＦｅＯＯＨを用いたＭｎ‐Ｚｎフェライトの配向性および磁気特性

Crystal oriented manganese zinc ferrites were made from acicular α-FeOOH, Mn(C5H7O2)3 and Zn(C5H7O2)2 as raw materials. The materials were mixed and calcined at 800°C for 4 hours in nitrogen atmosphere. The calcined acicular manganese zinc ferrite fine particles were formed into a thin troidal cores, consist of multi-layered. The green bodies were sintered at the range of 1100 to 1250°C for 4 to 8 hours in air, thereafter cooled in nitrogen atmosphere.The crystals of sintered manganese zinc ferrites were strongly oriented to the direction of {111} plane of the spinel, which was all formed along the upper plane of troidal cores. The behavior of crystal growth was similar to that of manganese zinc ferrite single crystal. The initial permeability of crystal oriented manganese zinc ferrites was 1380 at 0.1MHz and it was not allowed to decay up to 2.2 MHz at the operating condition of the 3dB decrease of the initial permeability. The high crystal orientation and suitable grain size has greatly contributed to the improvement of magnetic properties.

Epitaxial growth of [111] oriented manganese zinc ferrite thin films and their magnetic properties

Manganese zinc ferrite (MnZn ferrite) thin films were prepared on quartz substrates buffered by a ZnO underlayer by rf magnetron sputtering. The ZnO underlayers exhibited preferentially [001] orientation for any thickness. When Mn-Zn-Fe oxide layers as-deposited on the ZnO underlayers were annealed in reduced atmosphere at 800/spl deg/C for 5 hours, single-phase spinel type ferrites were formed. The films were preferentially oriented to the [111] direction normal to the film plane. Thin ZnO underlayers successfully induced [111] orientation in plane because of good lattice matching between the ZnO and the spinel phase. Films with a composition of Mn:Zn:Fe=23:9:68 had a saturation magnetization value of 410 emu/cm/sup 3/. The relationship between the composition and the magnetization for the films was similar to that for the bulk material.

Bonding between single-crystal manganese-zinc ferrites using electric field

Bonding between single-crystal manganese-zinc ferrites using electric field

Composition dependence of elastic behaviour of mixed manganese–zinc ferrites

Mixed Mn–Zn ferrites are prepared by the double sintering ceramic method. The ultrasonic compressional velocity ( V l) and shear velocity ( V s) in these ferrites are measured at room temperature by the ultrasonic pulse transmission technique. The elastic moduli of the specimens are computed and corrected to zero porosity. The variation of the elastic moduli with composition is interpreted in terms of binding forces between the atoms of the spinel lattice. The lattice parameters of the specimens are evaluated from the X-ray diffraction studies. The linear variation of these parameters with composition has been explained on the basis of the tetrahedral ionic radius.

Synthesis of Novel Magnetorheological Fluids

This article focuses on the synthesis and processing of novel magnetorheological (MR) fluids. The process for preparing MR fluids typically involves introducing magnetic particles into base liquid under low shear conditions. This is followed by ball milling in the fluid with zirconia (ZrO2) grinding media for about 24 h. High-purity carbonyi iron (Fe) powders have been used for the synthesis of ironbased MR fluids while the ferrite-based MR fluids used magnetic manganesezinc ferrite and nickel-zinc ferrite powders.Typical volume fractions of the magnetic phase that lead to MR fluids with respectable yield stresses tend to be about 0.3–0.5. Higher volume fractions, in principle, can lead to higher strength MR fluids. However, higher volume fractions tend to cause a significant, and often undesirable, increase in the “off-state” viscosity of the MR fluids. The rationale for selection and the role of different components of MR fluids are briefly discussed in the following sections.

Manganese-zinc ferrites with improved properties

Mn-Zn ferrites play an important role for the design of inductors in the frequency range from 10 kHz to 100 MHz. Important intrinsic properties such as crystalline anisotropy, magnetostriction, and their dependence on chemical composition are well known. All properties can be improved regarding the present state of the art. The experiments are related to the optimization of microstructure, esp. the control of grain growth in the range of I to 50 μm with a narrow distribution of the grain size, the insulation of the grain boundary and the control of defects. SEM and TEM was used to investigate the microstructure, amorphous interfaces and triple points of different additive systems. The following properties have been strongly influenced: Increase of initial permeability from 10.000 up to 20.000. Improvement of insertion loss for frequencies of up to 5 MHz for EMC applications. Decrease of power loss in the frequency range from 0.5 to I MHz for power applications. Therefore the use of optimized technology was necessary in order to obtain better homogenity of raw material and good densification of green bodies and optimum sintering. The sol-gel route gives a better chemical homogeneity, especially for sintering additives. The gained experiences hold out the prospect of improving the above mentioned properties furthermore.

Characteristics of the excitation of ultrasonic waves by thin wafers of manganese zinc ferrite single crystals

It is suggested that thin wafers of a magnetostrictive material may be used as emitters of rf ultrasound. Single crystals of manganese zinc ferrite, which have high magnetostriction constants and low Foucault current losses, were used to investigate the orientational field dependences of the efficiency of excitation of acoustic waves having different polarizations. Some distinguishing features of the excitation of sound by single-crystal wafers compared with polycrystalline samples were observed, and the direction of propagation and polarization of the sound wave and its polarization relative to the crystallographic axes of manganese zinc ferrite with the highest conversion efficiency was identified.

Hydrothermal synthesis and sintering of nickel and manganese-zinc ferrites

The influence of the starting materials on the crystalline phases observed after hydrothermal synthesis of nickel and manganese-zinc ferrites was investigated. The combination of sulfates and sodium hydroxide showed the best results for the conditions studied. The morphological parameters of MnZn ferrites produced at different hydrothermal conditions (110–190 °C, 4–30 h) were analyzed. Changes in lattice parameter, particle size, density, size and total volume of pores, and in the surface area of the particles were analyzed as a function of temperature and processing time. The sintering process was employed in order to verify the reactivity of the hydrothermal powders at controlled atmosphere. High density and surface homogeneous ceramic bodies were obtained, without zinc volatilization. Lattice parameter variations were associated with changes in the cations distribution of the spinel during sintering.

Control of a Segregation during Directional Solidification of the Manganese-Zinc Ferrite

The composition of the Znfe 2 O 4 - MnFe 2 O 4 , ferrite has been determined on the basis of pseudobinary phase diagram calculated on the assumption that chemical potential of both components are equal for both liquid and solid solutions. A single crystal has been produced applying method of the directional solidification. The open Bridgman system with oxygen atmosphere of a proper pressure, a positive temperature gradient, constant growth rate and continuous addition of an alloy of the nominal concentration has been applied. The chemical segregation along the longitudinal axis of obtained single crystal has been examined by means of scanning electron microscopy. The possibly small distances between analysed areas has been applied. Some obtained results of measurements have been compared with those of calculations. The improved Brody - Flemings' theory worked out for linear and parabolic movement of the local s/1 interface has been used for the calculations. The obtained micrographs have allowed to control considered segregation via theoretical prediction and decrease an inhomogeneity. For that reason three features of both theoretical and experimental curves have been differentiated and analysed.

Microemulsion processing of manganese zinc ferrites

Nanosized precursor particles of manganese zinc ferrites, Mn 0.45Zn 0.55Fe 2O 4, have been synthesized from inverse microemulsions of metal nitrates and aqueous ammonia solution. Two processing routes, namely, a single-microemulsion route and a double-microemulsion route, were studied and compared. The double-microemulsion-derived precursor led to the formation of ultrafine manganese zinc ferrite particles when calcined at 600 °C, although particle agglomeration had occurred.

Effects of MoO/sub 3/ addition on manganese zinc ferrites

We examined the effect of added MoO/sub 3/ on the initial permeability and other material characteristics in order to develop Mn-Zn ferrites with a high permeability. It was found that although MoO/sub 3/ addition could expand the diameters of crystalline grains, it could also promote porosity, thereby impeding grain growth. When the amount of MoO/sub 3/ was increased, the grain diameter expanded, peaked, and then gradually declined under the influence of porosity. However, by prolonging the top-temperature sintering period to curb porosity, it was possible to realize the grain-growth-promotion effect of MoO/sub 3/. Thus, we confirmed that high-permeability Mn-Zn ferrites could be obtained using a sintering technique which would enhance ferrite density.

Tailoring the microwave permittivity and permeability of composite materials

The microwave permittivity (ɛr) and permeability (µr) of composite materials are tailored by adding various loading agents to a host plastic and are subsequently modeled using the Maxwell Garnett theory and second order polynomials. With the addition of manganese zinc ferrite, strontium ferrite, nickel zinc ferrite, barium tetratitanate and graphite powders, materials with values of ɛ′, e″, µ′, µ″ as high as 22, 5, 2.5 and 1.7 have been obtained. Permittivity and permeability data are calculated at 2.0245 GHz from reflection and transmission measurements performed in a 7 mm coaxial test line. The Maxwell Garnett (MG) theory successfully models ɛr if the filling factor is less than 0.30 and ratio |ɛ1| (host)/ |ɛ2| (powder) is greater than 0.04. As this ratio decreases, the MG theory is shown to be independent of ɛ2 and second order polynomials are used to effectively model the dielectric constant. Polynomials are also used for the ferrite composites because it was determined that the MG theory was unable to model µr. This deficiency is attributed to the difference of domain structures that exist in powdered and sintered ferrites.