Magnetic Properties Of MnZn Ferrites Research Articles

Influence of ${\hbox{Fe}}_{2}{\hbox{O}}_{3}$ Stoichiometry on Initial Permeability and Temperature Dependence of Core Loss in MnZn Ferrites

We investigated the relationship between magnetic properties of MnZn ferrites and Fe2O3 stoichiometry by measuring magnetic properties, electrical resistivity, and density. We used a scanning electron microscope to observe the fractured surface of sintered samples. MnZn ferrites were prepared by adapting the conventional ceramic technique. Toroidal cores were sintered at 1355degC for 4 h with 4% oxygen. The results show that the initial permeability and power losses of MnZn ferrites strongly depend on the content of Fe2O3. And there is an obvious secondary maximum peak in the curve of mui versus T at about 100degC. The initial permeability mui reaches a maximum value and the power loss is lowest over a wide temperature ranging from 20degC to 180degC when the content of Fe2O3 is 52.5 mol%.

Influences of Bi 2O 3 on microstructure and magnetic properties of MnZn ferrite

MnZn ferrites were prepared by conventional oxide ceramic process. The effects of Bi 2O 3 on microstructure and magnetic properties of MnZn ferrites were investigated by means of characterizing the fracture surface micrograph, composition of grain boundary, magnetic properties and density by scanning electron microscope (SEM), energy dispersive X-ray spectroscope (EDS), B-H analyzer and Archimedes method, respectively. The results indicate that Bi 2O 3 mainly segregates and concentrates in the grain boundary regions, promotes solid-state reaction and grain growth, reduces porosity and enhances density. Optimum addition of Bi 2O 3 increases the permeability and saturation magnetic induction, meanwhile ensures the well frequency stability of permeability.

Development of MnZn ferrites by combinatorial synthesis and high throughput screening method

In this paper, the application of combinatorial synthesis and high throughput screening method to prepare low loss MnZn ferrite is investigated. The combinatorial synthesis and high throughput screening method is regarded as a novel technical method to develop new materials. It seems to be an attractive approach to fabricate MnZn ferrite, for it can accelerate rapid development, shorten research periods and save research funds. We analyze the technical route of the development of low power loss MnZn ferrite by this method in detail. Meanwhile, the influence of different dopants combination and sintering temperatures on magnetic properties of MnZn ferrites are discussed. Using this method, the prepared samples display higher magnetic performance, which can be applied in wider frequencies and temperatures range.

Controlling the Properties of Manganese-Zinc Ferrites by Substituting In3+ and Al3+ Ions

The effect of substitution of In3+ and Al3+ ions on the electrical and magnetic properties of Mn-Zn ferrites has been investigated. The substitution of In3+ ions for Fe3+ ions resulted in an increase of lattice parameter, owing to the larger size of In3+ ions, whereas lattice parameter was found to decrease on substituting Al3+ ions in place of the Fe3+ ions, owing to the smaller size of Al3+ ions. The dc resistivity was found to increase with the substitution of In3+ and Al3+ ions in the Mn-Zn ferrite system. The improvement in the dc resistivity has been observed at the expense of deterioration in the magnetic properties of Al3+ substituted Mn-Zn ferrites. A significant reduction in the values of initial permeability, saturation magnetization and Curie temperature was observed with successive increase of Al3+ ions. The saturation magnetization and initial permeability were found to increase with incorporation of In3+ ions. A marked increase in the value of initial permeability was found for the Mn0.4Zn0.6In0.5Fe1.5O4 ferrite. Curie temperature was found to decrease with an increase of In3+ ion concentration. These changes in the properties are explained on the basis of their magnetic interactions, a modified cation distribution and various models.

Magnetic properties and microstructures of SnO 2 doped Mn-Zn ferrites

The effects of additive SnO 2 (0.4wt. %), with and without SiO 2 (0.02wt. %) and/or CaO (0.04wt. %), on the microstructure and magnetic properties of Mn-Zn ferrites were reported. The results reveal that SnO 2 on its own increases the initial permeability (μi) slightly, but SnO 2 with SiO 2 and/or CaO decreases the values of μi. However, ferrites with SnO 2 additions have reduced power losses. The separate contributions of hysteresis loss and eddy current loss to the total power loss show that SnO 2(with or without SiO 2 and/or CaO) doping increases the hysteresis loss slightly, but SnO 2 doping alone reduces the eddy current loss significantly (∼ 14%). The additions of SiO 2 or CaO further decrease the eddy current loss, and by interaction of SnO 2-CaO-SiO 2, the eddy current loss is reduced by more than 20%. These magnetic and microstructural effects were discussed in terms of the additive-impurity interaction, the existence of grain boundary phases, and the effective bulk and grain boundary resistivities of the ferrites.

Microstructure and magnetic performance of Ni-substituted high density MnZn ferrite

The effects of NiO on microstructure and magnetic properties of Mn-Zn ferrite with a nominal composition of Zn 0.32Mn 0.60 -x Ni x Fe 2.08O 4 were investigated. The calcined powder of Mn-Zn ferrite was characterized by X-ray diffraction (XRD), the fracture surface of Mn-Zn ferrite was checked by scanning electronic microscope (SEM), and then the magnetic properties were measured. As a result, the substitution of Ni can cause the crystal lattice constant of MnZn ferrite to decline, and the grain size to decrease, therefore improve the magnetic performance of MnZn ferrite whose density exceeds 5.0 g·cm -3.

Effects of calcining and sintering parameters on the magnetic properties of high-permeability MnZn ferrites

For asymmetric digital subscriber line (ADSL) technology applications, new MnZn ferrites are required with not only high initial permeability, but also with low hysteresis material constant /spl eta//sub B/. The effects of calcining and sintering temperatures and oxygen equilibrium partial pressure on the magnetic properties of MnZn ferrites are studied in this work. It was found that raising the calcining temperature required a rise in the sintering temperature to simultaneously achieve maximum permeability and the lowest /spl eta//sub B/ value. Both grain size and porosity had an effect on the initial permeability of the samples. Porosity had an even larger effect on the /spl eta//sub B/ value than the initial permeability. Oxygen equilibrium partial pressure also had an important effect on the initial permeability and /spl eta//sub B/ value. In our testing range, both the initial permeability and the /spl eta//sub B/ value decreased with increasing value of A (oxygen parameter). In order to optimize synthesis conditions for the high initial permeability and low /spl eta//sub B/ value, it was best to calcine the sample at 950/spl deg/C and sinter it at 1370/spl deg/C, with A=7.55.

Neutron diffraction and ferromagnetic resonance studies on plasma-sprayed MnZn ferrite films

The magnetic properties of MnZn ferrites are affected by the plasma spray process. It is found that improvements can be made by annealing the ferrite films at 500°C–800°C. The annealing induced magnetic property changes are studied by neutron diffraction and ferromagnetic resonance techniques. The increase of the saturation magnetization is attributed to the cation ordering within the spinel lattice, which increases the magnetic moment per ferrite formula. The refinements on the neutron diffraction data suggest that the redistribution of the cation during annealing neither starts from a fully disordered state nor ends to a fully ordered state. The decrease of the coercivity is analyzed with the domain wall pinning model. The measurements on the magnetostriction and residual stress indicate that coercive mechanisms arising from the magnetoelastic energy term are not dominant in these ferrite films. The decrease of the coercivity for annealed ferrite films is mainly attributed to the decrease of the effective anisotropic field, which may result from the homogenization of the film composition and the reduction of the microstructural discontinuity (e.g., cracks, voids, and splat boundaries).

Effects of zinc loss on the magnetic properties of plasma-sprayed MnZn ferrites

Energy dispersive X-ray analysis performed on plasma-sprayed MnZn ferrite (MZF) single `splats' shows a variation in zinc content within splats of different sizes after the spray process, even though the powder has the same starting stoichiometry. A simple model indicates that smaller particles have a higher zinc evaporation rate during the in-flight time. However, the significant decrease of zinc in smaller ferrite particles is mainly attributed to their large surface-to-volume ratio. Compositional differences due to a random cation distribution condition results in magnetic property variations among MZF splats. The coating inhomogeneity due to zinc loss increases the coercivity of the plasma-sprayed MnZn ferrites. The magnetic properties of the MnZn ferrites can be improved through long-range (diffusion) and short-range (ordering) cation redistribution upon low temperature annealing.

Structure related magnetic properties of MnZn ferrite with ultra-fine grain structure

Nanostructured ferrites have been prepared by milling starting from commercial ferrite powders. Subsequent compaction and sintering were applied to obtain cylindrical pieces. The magnetization as a function of the grain size follows the non magnetic grain boundary (NMGB) model. The boundary thickness is estimated as about 1.5 nm, which is consistent with that calculated from the Mossbauer absorption areas. Due to the high lattice distortion, the small exchange length impedes the averaging of the anisotropy.

Magnetic properties of MnZn ferrite with ultra-fine grain structure

Nanostructured ferrites have been prepared by milling starting from commercial ferrite powders. Subsequent compaction and sintering were applied to obtain cylindrical pieces. The magnetization as a function of the grain size follows the non-magnetic grain boundary model. The boundary thickness is estimated as about 1.5 nm, which is consistent with that calculated from the Mössbauer absorption areas. Due to the high lattice distortion, the small exchange length impedes the averaging of the anisotropy.

The effect of Nb 2O 5 dopant on the structural and magnetic properties of MnZn-ferrites

In the present work, the role of Nb 2O 5 additions on the structural and electromagnetic properties of MnZn-ferrites has been investigated. Nb 2O 5 additions at a concentration of about 200 ppm are found to lower the losses by almost 17%. At higher concentrations Nb 2O 5 segregates at the grain boundaries, promotes grain growth and affects negatively the microstructure development. At concentrations up to 200 ppm, where a gradual improvement of the magnetic properties is observed, Nb 2O 5 is found to precipitate together with CaO homogeneously along the grain boundaries and participates in the formation of glassy phases. Those phases act as buffers between the grains, smoothening the transition from one grain to the other. Moreover they also reduce Zn-evaporation at the grain boundary area. Both effects are in favour of low electromagnetic power losses and of high relative magnetic permeabilities.

Microstructure dependence of AC magnetic properties in Mn-Zn ferrites

A correlation between microstructure and frequency dependent magnetic properties of Mn-Zn ferrites was established using the inductance spectroscopy method. Several atmosphere conditions and dwell times and temperatures were used during sintering to obtain a variety of microstructures in samples of different compositions. Results show that initial permeability (/spl mu//sub i/) strongly depends on the atmosphere composition during sintering, it increases, while relaxation frequency (f/sub r/) slightly decreases as oxygen content decreases. On the other hand, dwell times longer than three hours led to a slight decrease in permeability (/spl mu/) and an increase in f/sub r/. For the compositions prepared, a systematic decrease in /spl mu/ was observed as zinc content decreases, regardless of the sintering conditions used. For each composition a maximum in /spl mu/ was obtained for the same sintering conditions, which also correspond to the highest density values.

Magnetic properties of MnZn ferrites prepared by soft chemical routes

MnZn ferrites with different composition have been synthesized by soft chemistry routes using oxalate precursors with the partial replacement of water by acetone as the solvent. Toroids were sintered at 1250 °C for 3 h in O2/N2 atmosphere. Sintering conditions significantly changed macroscopic characteristics as density and initial permeability for different composition. Variation of the complex permeability with frequency have been measured over a wide range of frequency, up to 1.8 GHz where dispersion is attributed to spin resonance. No additives for increasing densification were employed. Samples exhibit the highest permeability values for Mn0.8Zn0.2Fe2O4. An anomalous effect is observed when copper is added to MnZn ferrites. The initial permeability (μi) values do not exhibit much variation with temperature, except near Tc where it falls sharply. Curie point and magnetic losses are related with composition.

ＴｉＯ２を添加したＦｅ‐ｐｏｏｒ組成Ｍｎ‐Ｚｎフェライトの周波数特性

It has been difficult to use Mn-Zn ferrite at a frequency range beyond 1 MHz due to its low electrical resistivity. We have been trying to improve the resistivity and magnetic properties of Mn-Zn ferrite by alterations of the composition and additives. We found that the combination of Fe-poor composition (less than 50 mol % of Fe2O3) and the addition of TiO2 to Mn-Zn ferrite produced a remarkable increase in resistivity and an improvement in initial permeability at high frequencies. In addition, this ferrite unexpectedly could be sintered in air, unlike the conventional Fe-rich ferrite. The representative Fe-poor ferrite (48.5F2O3-30.3MnO-20.2ZnO-1.0TiO2) showed a very high permeability of μi = 200 at 10 MHz. The manufacturing process and the attractive magnetic properties at high frequency of the Fe-poor Mn-Zn ferrite are discussed.

High‐Resistivity Grain Boundaries in CaO‐Doped MnZn Ferrites for High‐Frequency Power Application

The microstructural development and magnetic properties of MnZn ferrites doped with various amounts of CaO and sintered in atmospheres containing various oxygen concentrations were investigated. The results indicate a strong link among the amount of CaO segregated in the grain boundary, the oxygen concentration during sintering, the average grain size, and the magnetic properties of the MnZn ferrites.

亜鉛浸出残さの脱鉄処理で得られる酸化鉄の精製と磁化特性に及ぼす事前水洗とＮａ２Ｂ４Ｏ７フラックス添加量低減の影響

The purification of raw iron oxide obtained from iron precipitation of the zinc leach residue using the recrystallization method with Na2B4O7 flux and their magnetic properties has been investigated. The main purpose of present study are to examine the effect of the prior water washing and decrease of amounts of Na2B4O7 flux on the purification of raw material. As a result, it was recognized that the prior water washing of raw material are undesirable, because of decrease of desulfurization in the purification by the sub-sequent recrystallization method,and the elimination of Zn, S and As in raw material is the best, when raw material/flux ratio is 70/30 and the prior water washing is not carried out. The magnetic properties is similar to that of α-Fe2O3 single crystal. The synthesis and magnetic properties of Mn-Zn ferrite from purified iron oxide were also examined.

Atmosphere Controlled Roller Hearth Kiln for High Performance Mn-Zn Ferrites

A new roller hearth kiln(RHK) has been developed, which satisfies not only the highest quality of Mn-Zn ferrites, but also large quantity of production. Using the RHK (the length is 50m), the total sintering time is reduced to less than 11 hours, that is shorter than the half of the case of pusher kiln. Then the productive capacity of the RHK achieved 100 ton per month. Moreover, the control of oxygen content during sintering and the subsequently cooling is performed precisely, so that two different types of Mn-Zn ferrite, i.e. high-permeability and low power loss materials, can be sintered simultaneously in the RHK. The electromagnetic properties of these materials reach to the highest level in mass production. This paper describes the basic structure and the characteristics of the new RHK, and shows the magnetic properties of Mn-Zn ferrites which are sintered by the RHK.

The Effect of V2O5 Addition on the Microstructure and Magnetic Properties of Mn-Zn Ferrites

In response to the need for the improvement of low-loss core materials used for high-frequency power transformers, microstructures and magnetic properties of Mn-Zn ferrite have been investigated with the addition of CaO, SiO 2 and V 2 O 5 . The specimens of (Mn 0.72 Zn 0.22 O) 0.94 (Fe 2 O 3 ) 1.06 composition are prepared from the powders synthesized by SHS (Self-propagation High-temparture Synthesis) process. The presence of V 2 O 5 in the addition to the CaO SiO 2 results in a fine grain structure and suppress the abnormal grain growth. The electrical resistivity increases with the addition of V 2 O 5 , which is believed to he attributed to the melting of V 2 O 5 and formation of liquid phase at grain boundaries. The eddy-current loss is, therefore, lowered with addition of V 2 O 5 . However, if V 2 O 5 is over-weighted above an optimum value, the hysteris loss becomes dominant and therefore, the total core-loss increases.

Electric and Magnetic Properties of Ta-Doped Polycrystalline Mn-Zn Ferrite

The effect of Ta2O5 additive on the electric and magnetic properties of MnZn ferrites with fine grain size was studied A adding small amounts of Ta2O5 to the MnZn ferrite increased electric resistivity, while an excessive addition of Ta2O5 caused decrease in resistivity without significant grain growth. In a small amount of Ta2O5 the change in the electric resistivity can be explained by Ta 5+ substitution for Fe 3+ entailing disappearance of the oxygen defects. The excessive addition of Ta2O5 created the oxygen defects and the electrons which are promoted by the metallic ion defects and the thermal dissociation of oxygen.