Fabrication and performance optimization of Mn-Zn ferrite/EP composites as microwave absorbing materials

Magnesium-substituted Mn0.8Zn0.2Fe2O4 ferrite is synthesized by the sol–gel combustion method using citrate acid as the complex agent. The electromagnetic absorbing behaviors of ferrite/polymer coatings fabricated by dispersing Mn–Zn ferrite into epoxy resin （EP） are studied. The microstructure and morphology are characterized by X-ray diffraction and scanning electron microscope. Complex permittivity, complex permeability, and reflection loss of ferrite/EP composite coating are investigated in a low frequency range. It is found that the prepared ferrite particles are traditional cubic spinel ferrite particles with an average size of 200 nm. The results reveal that the electromagnetic microwave absorbing properties are significantly influenced by the weight ratio of ferrite to polymer. The composites with a weight ratio of ferrite/polymer being 3：20 have a maximum reflection loss of –16 dB and wide absorbing band. Thus, the Mn–Zn ferrite is the potential candidate in electromagnetic absorbing application in the low frequency range （10 MHz–1 GHz）.

Development and application of ferrite materials for low temperature co-fired ceramic technology

Development and application of ferrite materials for low temperature co-fired ceramic （LTCC） technology are dis- cussed, specifically addressing several typical ferrite materials such as M-type barium ferrite, NiCuZn ferrite, YIG ferrite, and lithium ferrite. In order to permit co-firing with a silver internal electrode in LTCC process, the sintering temperature of ferrite materials should be less than 950 ℃. These ferrite materials are research focuses and are applied in many ways in electronics.

Microwave left-handed composite material made of slim ferrite rods and metallic wires

This paper reports on experimental study of the microwave properties of a composite material consisting of ferrite and copper wires. It finds that the slim ferrite rods can modify the magnetic field distribution through their anisotropy, so that the ferrite＇s negative influence on the copper wires＇ plasma will be reduced. Left-handed properties are observed even in the specimen with close stuck ferrite rods and copper wires.

Preparation and Sinterability of Mn-Zn Ferrite Powders by Sol-Gel Method

Mn-Zn spinel ferrites were synthesized by sol-gel method. Effects of calcined temperature on structure and particle size of MnZnFe2O4 were investigated by X-ray diffraction (XRD) and scanning electron microscopy (SEM). XRD patterns indicate that the ultra fine Mn-Zn ferrite exhibits a spinel crystal structure. SEM images show that the powder fired at 900℃for 2 h has an average diameter of 60 ~ 90 nm. The particle size becomes larger with the increasing of calcined temperature and the distribution of particle becomes even more homogeneous. Sintering behaviors of synthesized ferrite powders depend on the powder characteristics and high temperatures have induced the good crystallization of particles.

Effects of Ce^(3+) doping on the structure and magnetic properties of Mn-Zn ferrite fibers

Ce3+-doped Mn-Zn ferrite fibers were successfully prepared by the organic gel-thermal decomposition method from metal salts and citric acid. The composition,structure,and magnetic properties of these ferrite fibers were characterized by X-ray diffraction (XRD),scanning electron microscopy (SEM),and vibrating sample magnetometer (VSM). The results show that Mn0.2Zn0.8Fe2-xCexO4 (x = 0-0.04) fibers are featured with an average grain size of 11.6-12.7 nm,with diameters ranging between 1.0 to 3.5 μm and a high ...

Effects of Heating Processing on Microstructure and Magnetic Properties of Mn-Zn Ferrites Prepared via Chemical Co-precipitation

The fine powders of Mn-Zn ferrites with uniform size were prepared via chemical co- precipitation method. X-ray diffraction analysis （XRD）, scanning electron microscopy （SEM）, vibrating sample magnetometer （VSM）, frequency dependence of permeability and metallographical microscope were used to investigate the crystal structure, surface topography and magnetic properties of the powders and the sintering samples. The experimental results demonstrate that the precursor powders have formed a pure phase cubic spinel MnxZn1-xfe2O4 while in the reactor and show definite magnetism, which can solve the difficult issue in washing process effectively. When calcined beneath 450 ℃, the powders have intact crystal form and the crystallite size is less than 20 nm. Comparison tests of sintering temperatures show that 1 300 ℃ is the ideal sintering temperature for Mn-Zn ferrites prepared by using the chemical co-precipitation.

Preparation and Magnetic Properties of Mn-Zn Ferrites by the Co-precipitation Method

Mn-Zn ferrites （Mn1-xZnxFe2O4） with different compositions were prepared by the coprecipitation method, and the influences of such synthesis conditions as pH value, composition and volume ratio （R） of the mixed solution and NH4HCO3 solution on their microstructures and magnetic properties were discussed. The samples were characterized by X-ray diffraction （XRD） and magnetization measurement instrument. Lattice parameters and average crystalline size of the synthesized materials were calculated from the corresponding XRD patterns with the related software Jade.5. For samples of different pH values, only one phase was found when pH values were 7.0, 8.0 and 9.0. The sample with pH value of 7.0 exhibited the highest saturation magnetic induction, the lowest coercive force, and crystallized best. For samples of different R values with pH value of 7.0, only one phase was observed in all samples, and the sample with R value of 2.3 exhibited the highest saturation magnetic induction and the lowest coercive force. The composition has mainly afected the magnetic properties, and the saturation magnetic induction increases with the increase of the content of Zn （x）, but decreases when x is beyond 0.6. The trend of coercive force is on the contrary. However, no magnetism is exhibited when the x value is up to 0.8.

Magnetic properties and microstructures of SnO_2 doped Mn-Zn ferrites

The effects of additive SnO2 (0.4wt.%), with and without SiO2 (0.02wt.%) and/or CaO (0.04wt.%), on the microstructure and magnetic properties of Mn-Zn ferrites were reported. The results reveal that SnO2 on its own increases the initial permeability (μi) slightly, but SnO2 with SiO2 and/or CaO decreases the values of μi. However, ferrites with SnO2 additions have reduced power losses. The separate contributions of hysteresis loss and eddy current loss to the total power loss show that SnO2 (with or without SiO2 and/or CaO) doping increases the hysteresis loss slightly, but SnO2 doping alone reduces the eddy current loss significantly (～14%). The additions of SiO2 or CaO further decrease the eddy current loss, and by interaction of SnO2-CaO-SiO2, 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.

Effect of V2O5-CaCO3-Nb2O5 Contents on Properties of Low Power Loss Mn-Zn Ferrites

Effect of the content of dopants in the manganese-zinc ferrites on the low power loss is studied by measuring magnetic properties and observing the grain boundary structures. The Mn0.738Zn0.206Fe2.066O4 composition powders were prepared by using conventional ceramic powder processing technique. The microstructure of grain boundary was observed by scanning electron microscope （SEM）. It has been found that power loss is greatly dependent upon the content of the additives.

Magnetic Hysteresis and Complex Initial Permeability of Cr³⁺Substituted Mn-Zn Ferrites

The impact of Cr3+ ion on the magnetic properties of Mn0.50Zn0.50CrxFe2-xO4 (with x = 0.0, 0.1, 0.2, 0.3, 0.4 and 0.5) has been studied. Ferrite samples were synthesized by combustion method and sintered at various temperatures (1250°C, 1300°C and 1350°C). The structural properties were investigated by means of X-ray diffraction patterns and indicated that the samples possess single phase cubic spinel structure. The lattice parameter decreases with the increase in Cr3+ content, as the ionic radius of Cr3+ ion is smaller than that of Fe3+. The average grain size (D), bulk density (ρB) and initial permeability (μi’ )decreases with increase in Cr3+ content whereas porosity follows its opposite trend. The ρB was found to increase with increase in Cr3+ content as the sintering temperature (Ts) is increased from 1250°C to 1350°C. The Ts affects the densification, grain growth and (μi’ ) of the samples. The (μi’ ) strongly depends on average grain size, density and intragranular porosity. The B-H loops of the compositions were measured at room temperature. The saturation magnetization (Ms), coercivity (Hc) and hysteresis losses were studied as a function of Cr3+ content. The Ms was found to decrease with the increase of Cr3+ content, which is attributed to the dilution of A-B interaction.

Effect of Nd Doping on Nanosized Mn-Zn Ferrite

Nanosized Mn-Zn ferrite doped with Nd (Mn_ 0.6Zn_ 0.4Nd_xFe_ 2-xO_4) were fabricated by hydrothermal precipitation route and studied by XRD, TEM, DSC and VSM. The effects of Nd doping on manganese zinc ferrites were discussed. The results show that the samples with a small amount of Nd doping are spinel crystal structure and uniformly nanosized particles with little aggregation. DSC analysis of Mn_ 0.6Zn_ 0.4Fe_2O_4 and Mn_ 0.6Zn_ 0.4Nd_ 0.06Fe_ 1.94O_4 samples both present two exothermic peaks ascribed to the redistribution of Mn 2+, Zn 2+ and Fe 3+ ions in the two sub-lattices (tetrahedral (A) and octahedral (B) sites), and the oxidation of Mn 2+-ions at higher temperatures respectively. The saturation magnetization (M_s) for Mn_ 0.6Zn_ 0.4Nd_xFe_ 2-xO_4 ferrites increase with (x) up to 0.06 and decrease for higher concentrations. And supermagnetic behavior was observed at 25 ℃ in the M-H loops of Mn_ 0.6Zn_ 0.4Fe_2O_4 and Mn_ 0.6Zn_ 0.4Nd_ 0.06Fe_ 1.94O_4 samples for their extremely small sizes.

Sintering process and grain growth of Mn-Zn ferrite nanoparticles

The density, microstructure and magnetic properties of non-doped Mn-Zn ferrite nanoparticles sintered compacts were investigated. The compacts of non-doped Mn-Zn ferrite nanoparticles were sintered by segmented-sintering process at lower sintering temperature. The density of sintered samples was measured by Archimedes method, and the phase composition and microstructure were examined by XRD and SEM. The sintered Mn-Zn ferrite magnetic measurements were carried out with Vibrating Sample. The results show that the density of sintered compacts increases with the rising of sintering temperature, achieving 4.8245 g·cm-3 when sintered at 900 ℃, which is the optimal density of Mn-Zn functional ferrite needed and from the fractured surface of sintered samples, it can be seen that the grain grows well with small grain size and homogeneous distribution.

Effect of Sintering Temperature on Microwave Absorbing Behaviour of Mn-Zn Ferrite

The microwave absorbing behaviour of Mn-Zn ferrite sintered at 1100,1200,1300,1400 and 1500℃ has been investigated.The phase constitution of the ferrite was analyzed by X-ray diffraction.The results show that the ferrite sintered at 1 500℃ has better microwave absorbing prop- erty than those prepared at other temperatures,due to the increase of turbulent loss generated by the formation of excessive Fe^(2+) in deoxidizing of Fe_2O_3 at high temperatures.

Influence of Processing Parameters on the Magnetic Properties of Mn-Zn Ferrites

Pure MnO2, ZnO and Fe2O3 were used to prepare a Mn-Zn Ferrite sample of the nominal composition Mn0.64Zn0.29Fe2.07O4. These oxides were mixed firstly for 1hr, and then were milled for 20 and for 40 hrs. The as-mixed and the milled powders were examined by XRD and ME spectroscopy. The investigated samples were further mixed with PVA, granulated, cold pressed and sintered at different temperatures (1000, 1300 and 1400 oC) for 2 hrs and were then reinvestigated again. The magnetic properties of all samples before and after sintering were characterized using VSM at a field of 15 k Oe. When the powder oxides were milled for 20 hrs, detectable diffusion reaction was observed where the centers of all XRD peaks (due to Fe2O3 and MnO2) shifted to higher 2? angles, suggesting that Zn2+ cations had diffused through Fe3+ and/or Mn4+ lattices. The observed increase in the width of the XRD peaks can be attributed to the refinement of the powders by milling. Milling of the powder for 40 hrs resulted in the formation of spinel phase of (Zn, Fe), but MnO2 was disappeared probably due to the formation of amorphous structure. Sintering at 1000, 1300, and 1400 oC resulted in the formation of different spinel (Mn-Zn) ferrites. The ME measurements followed the gradual formation the manganese zinc ferrite until complete formation which observed in the sample that milled for 40 hrs followed by sintering at 1300 oC for two hrs. However, it can be concluded that, the processing conditions of such sample represent are the best conditions for obtaining a soft manganese zinc ferrite (single phase).

The Influence of Zn²⁺Ions Substitution on the Microstructure and Transport Properties of Mn-Zn Nanoferrites

The effect of Zn2+ ions on the microstructure and electrical properties of Mn1-xZnxFe2O4 (0.0 ≤ x ≤ 0.5 in steps of 0.1) through a solid state reaction has been investigated. The structural properties have been investigated using X-ray diffraction (XRD) technique. The XRD analysis confirms that all samples are in a single-phase cubic spinel structure. The experimental lattice parameter (aexp) was decreased with increasing Zn2+ ions substitution due to the smaller ionic radius of zinc content. The crystallite size (t) of samples was estimated by Scherrer’s formula and found in the range (90 - 115 nm). Dc electrical resistivity and Seebeck voltage coefficients were measured as a function of temperature using the two probe methods. The temperature variation of resistivity exhibits two breaks, each break referring to a change in the activation energy. The Curie temperature estimated from dc resistivity measurement decreases with increasing Zn2+ ions. Seebeck voltage coefficient measurements reveal n-type conduction for all samples.

Research progress of permanent ferrite magnet materials

Permanent ferrite magnet materials are extensively employed due to their exceptional magnetic properties and cost-effectiveness.The fast development in electromobile and household appliance industries contributes to a new progress in permanent ferrite materials.This paper reviews the deveolpement and progress of permanent ferrite magnet industry in recent years.The emergence of new raw material,the advancement of perparation methods and manufacturing techniques,and the potential applications of permanent ferrite materials are introduced and discussed.Specifically,nanocrystallization plays a crucial role in achieving high performance at a low cost and reducing reliance on rare earth resources,and therefore it could be a promising development trendency.

Electromagnetic and microwave absorbing properties of W-type barium ferrite doped with Gd^(3+)

W-type barium ferrites doped with Gd^3＋,Ba1-xGdx（Zn0.3Co0.7）2Fe16O27（x = 0,0.05,0.10,0.15,0.20）,were prepared by a sol-gel method.The effects of Gd^3＋ substitution on their microstructure,electromagnetic properties and microwave absorptive behavior were analyzed.The XRD patterns showed the single phase of W-type barium ferrite when x ≤ 0.15.Microwave electromagnetic properties of samples were studied at the frequency range from 2 GHz to 18 GHz using a network analyzer（Agilent 8722ET）.The complex permittivity ε（ε＇,ε＇＇） increased gradually when x ≤ 0.10,but it decreased as x = 0.15.The real permeability（μ＇） decreased with the increase of Gd^3＋ content,while the imaginary permeability（μ＇＇） increased when x ≤ 0.10.All these reasons were discussed using the electromagnetic theory.Furthermore,the ferrite-epoxy compound coating materials with 80 wt.% of Ba0.9Gd0.1（Zn0.3Co0.7）2Fe16O27 were prepared to measure the microwave absorbing properties.The maximum of reflection loss（RL） reached about-27 dB and RL was below-10 dB in the frequency range of 8-18 GHz when the thickness was 1.92 mm.

High Efficiency ELID Grinding of Garnet Ferrite

Hard and brittle materials such as ferrite, optical glass and ceramics have been widely used in many fields because of their good characteristics and still gain more attentions. However, it is difficult to machine and get good surface quality. Some parts made of these materials have large machining allowances and need to be produced with large batch, but the machining efficiency is very low with usual grinding method. So it is of great importance to research the high efficiency grinding technology of hard and brittle materials. Electrolytic in-process dressing (ELID) grinding is a new grinding technology which has been adopted to the ultra-precision machining of hard and brittle materials. With the function of in-process dressing of metal bond diamond and CBN wheel, ELID grinding has the ability to keep the sharpness of the wheel surface and is widely used in fine abrasive grinding, but it also has the potentialities to high efficiency grinding. In this paper, the mechanism of ELID grinding and its grinding performance are analyzed, then the cast iron bond diamond wheels and ELID grinding device are used on a surface grinder to research the feasibility of ELID grinding to high efficiency grinding. To make comparison, the garnet ferrite (YAG) work piece has been machined in plunge grinding both by ELID grinding and by the resin bond diamond wheel. The grinding force and surface quality are tested and analyzed. It has been found that the grinding force of the cast iron bond diamond wheel with ELID grinding is apparently smaller than that of the resin bond diamond wheel. Under the same conditions, it is about 2/5～3/5 as the force using the resin bond diamond wheel. So with the same grinder and machining conditions, ELID grinding can machine work piece with greater depth of cut. Because of the smaller grinding force, it is also beneficial to avoid the edge collapse of the work piece and keep the integrity of the grinding surface. This experiment shows that the grinding efficiency can be highly improved and the surface quality be ensured by applying ELID grinding technology and adopting large grinding depth. The results indicate that the ELID grinding technology can be effectively used in the high efficiency machining of garnet ferrite and other hard and brittle materials.

CoFe_2O_4-Graphene Nanocomposites Synthesized through An Ultrasonic Method with Enhanced Performances as Anode Materials for Li-ion Batteries

Co Fe2O4-graphene nanosheets(Co Fe2O4-GNSs) were synthesized through an ultrasonic method, and their electrochemical performances as Li-ion battery electrode were improved by annealing processes. The nanocomposites obtained at 350 °C maintained a high specific capacity of 1,257 m Ah g-1even after 200 cycles at 0.1 A g-1. Furthermore,the obtained materials also have better rate capability, and it can be maintained to 696, 495, 308, and 254 m Ah g-1at 1, 2,5, and 10 A g-1, respectively. The enhancements realized in the reversible capacity and cyclic stability can be attributed to the good improvement in the electrical conductivity achieved by annealing at appropriate temperature, and the electrochemical nature of Co Fe2O4 and GNSs during discharge–charge processes.

Synthesis and Characterization of Gadolinium Doping M-type Hexagonal Barium Ferrite Ultrafine Powders

The hexagonal BaGd x Fe 12- x O 19 ( x =0.1～1.0) nano sized powders with M type structure were synthesized by the sol gel auto combustion high temperature synthesis method. The effects of pH of the solution, the molar ratio of nitrate/citric acid and the calcination temperature on the synthesis of the ferrites were investigated. The crystal structure, grain size, shape and magnetic properties were studied by means of XRD, TEM and vibrating sample magnetometer.The results show that under the conditions of pH 7.0 or so, mole ratio of citrate/nitrate (1～3) and calcination temperature of 850 ℃ for 1 h, M type BaGd x Fe 12- x O 19 ultrafine powders with a particle size of less than 100 nm can be obtained, and the coercive force reaches 430 kA·m -1 at x =1.0, which is far greater than that of barium ferrite (BaFe 12 O 19 ).