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.

Structure and magnetic properties of Zn ferrite nanoparticles

A series of ZnxFe3-xO4（x = 0, 0. 15, 0. 30, 0o 40, 0. 48, 0. 60, 0. 70 ） nanoparticles prepared by hydrothermal method are studied by use of transmission electron microscope, X-ray diffraction, vibrating sample magnetometer, superconducting quantum interference device magnetometer and Mossbauer spectrometer. All samples present a spinel structure. The lattice constant increases with the increase in the Zn content while the grain size decreases from 18 nm to 9 nm. Moreover, the saturation magnetzafion at 5 K and 293 K increases initially when x ≤ 0. 40 and subsequently decreases when x 〉 0. 40. At room temperature, Mossbauer spectra exhibit a change from a well-defined sextet spectrum to a doublet spectrum as the Zn content increases. The doublet spectrum begins to appear when x = 0. 6, while it begins when x = 0. 80 for the bulk materials. The results of magnetization and Curie temperature measurements indicate that the doublet spectrum is due to the surperparamagnetic state of the nanoparticles. Furthermore, the relationship between the hyperfine field variation and the cation distribution is discussed. The variation of magnetic properties is interpreted by the three-sublattice Yafet-Kittel （Y-K）model.

Effects of Mg substitution on the structural and magnetic properties of Co0.5Ni（0.5-x）MgxFe2O4 nanoparticle ferrites

In this study, nanocrystalline Co-Ni-Mg ferrite powders with composition Coo.5Nio.5-xMgxFe2O4 are successfully synthesized by the co-precipitation method. A systematic investigation on the structural, morphological and magnetic properties of un-doped and Mg-doped Co-Ni ferrite nanoparticles is carried out. The prepared samples are characterized using x-ray diffraction （XRD） analysis, Fourier transform infrared spectroscopy （FTIR）, field emission scanning electron microscopy （FESEM）, and vibrating sample magnetometry （VSM）. The XRD analyses of the synthesized samples confirm the formation of single-phase cubic spinel structures with crystallite sizes in a range of - 32 nm to - 36 nm. The lat- tice constant increases with increasing Mg content. FESEM images show that the synthesized samples are homogeneous with a uniformly distributed grain. The results of IR spectroscopy analysis indicate the formation of functional groups of spinel ferrite in the co-precipitation process. By increasing Mg2- substitution, room temperature magnetic measurement shows that maximum magnetization and coercivity increase from - 57.35 emu/g to - 61.49 emu/g and - 603.26 Oe to 684.11 Oe （l Oe = 79.5775 A.m-l）, respectively. The higher values of magnetization Ms and Mr suggest that the opti- mum composition is Co0.5Ni0.4Mg0.1Fe204 that can be applied to high-density recording media and microwave devices.

Effect of Zn^(2+) Content on the Microstructure and Magnetic Properties of Nanocrystalline Ni_(1-x)Zn_xFe_2O_4 Ferrite by a Spraying-coprecipitation Method

Nanocrystalline Ni1-xZnxFe2O4 ferrites with 0≤x≤1 were successfully prepared by a spraying-coprecipitation method.The microstructure was investigated by using XRD and TEM.Magnetic properties were measured with vibrating sample magnetometer（VSM） at room temperature.The results show that the grain size of nanocrystalline Ni1-xZnxFe2O4 ferrite calcined at 600 ℃ for 1.5 h is about 30 nm.Lattice parameter and specific saturation magnetization Ms of nanocrystalline Ni1-xZnxFe2O4 ferrite increase with the Zn^2＋ ions content at room temperature,and maximum Ms is 66.8 A·m^2·kg^-1 as the Zn^2＋ ions content is around 0.5,and coercivity Hc of the nanocrystalline Ni1-xZnxFe2O4 ferrite decreases with Zn^2＋ ions content.

Preparation, Characterizations and Magnetic Properties of Doped Barium Hexaferrites BaFe_(12-2x)Mn_xSn_xO_(19) (x = 0.0-1.0)

A series of doped barium hexaferrites BaFe12-2xMnxSnxO19 （x = 0.0-1.0） particles were prepared by the co-precipitation/molten salt method. The particle size and crystalline of the samples BaFe12-2xMnxSnxO19 decrease with an increase in the doping amount x. When x is less than 0.8, the pure BaFe12-2xMnxSnxO19 particles with hexagonal plate morphology are obtained. The effects of substitution on magnetic properties were evaluated and compared to nomal BaFe12O19. The specific magnetizations （Ms） of doped materials have been significantly improved. Among all these compositions, the BaFe10.4Mn0.8Sn0.8O19 sample has the highest Ms value of 81.8 A？m2？kg-1 at room temperature and its intrinsic coercivity （Hc） is 44.5 kA？m-1. The as-prepared doped barium ferrites exhibit a low temperature coefficient of coercivity close to zero. The coercivity is independent of temperature when x is in the a range 0.5-0.7.

Effect of High-Energy Ball Milling on the Magnetic Properties of NiZn Ferrite Ceramics Synthesized by Spark Plasma Sintering

High-density fine-grained Ni0.5Zn0.5Fe2O4 ferrite ceramics were synthesized by spark plasma sintering (SPS) in conjunction with high energy ball milling. The precursor powders were milled for 20 h, 40 h, and 60 h, respectively, and the milled powders were all sintered for 5 min at 900&degC. All the samples exhibit a single spinel phase. With increasing of the ball milling time, the relative density of the samples increases (up to 97.7%), however, the grain size decreases (down to ~200 nm). At room temperature, the sample from the 40 h-milled powder has the best combination of saturation magnetization and coercivity (83 emu/g and 15 Oe). These outstanding magnetic properties may be associated with high density and uniform microstructure created by SPS on the basis of fine precursor powders produced by high-energy ball milling.

Review of recent advances in ferrite-based materials:From synthesis techniques to electromagnetic wave absorption performance

With the booming development of electronic information science and 5G communication technology,electromagnetic radi-ation pollution poses a huge threat and damage to humanity.Developing novel and high-performance electromagnetic wave(EMW)ab-sorbers is an effective method to solve the above issue and has attracted the attention of many researchers.As a typical magnetic material,ferrite plays an important role in the design of high-performance EMW absorbers,and related research focuses on diversified synthesis methods,strong absorption performance,and refined microstructure development.Herein,we focus on the synthesis of ferrites and their composites and introduce recent advances in the high-temperature solid-phase method,sol-gel method,chemical coprecipitation method,and solvent thermal method in the preparation of high-performance EMW absorbers.This review aims to help researchers understand the advantages and disadvantages of ferrite-based EMW absorbers fabricated through these methods.It also provides important guidance and reference for researchers to design high-performance EMW absorption materials based on ferrite.

Synthesis of nickel ferrite precursors from low grade nickel matte

Fine nickel ferrite precursors NiFe2（C204）3·6H2O were obtained via co-precipitation method with low grade nickel matte as the raw material. Thermodynamic analysis of NiClz-FeC12-（NH4）2C204-H20 system for precipitation identified that the theoretical optimum co-precipitation pH value is 2, and C2O2 has strong complexation with Ni2＋ and Fe2＋ ions. Based on these theoretical considerations, the effects of parameters on the precipitation rates and precursors size were investigated systematically. The results show that the optimum co-precipitation conditions are pH=2, temperature 45 ℃, 1.2 times theoretical amount of （NH4）2C204 dosage and 3% PEG400 addition. Under these conditions, the precipitation rates of Ni2＋ and Fe2＋ are both over 99.8%, with the precursors size of 1-2 urn. Furthermore, X-ray diffraction （XRD） and thermogravimetry-differential thermal analysis （TG-DTA） demonstrate that the precursors are single-phase solid solution, wherein the nickel/iron atoms are replaced by the iron/nickel atoms reciprocally.

Growth of monodisperse nanospheres of MnFe_2O_4 with enhanced magnetic and optical properties

Highly dispersive nanospheres of MnFe204 are prepared by template free hydrothermal method. The nanospheres have 47.3-nm average diameter, narrow size distribution, and good crystallinity with average crystallite size about 22 nm. The reaction temperature strongly affects the morphology, and high temperature is found to be responsible for growth of uniform nanospheres. Raman spectroscopy reveals high purity of prepared nanospheres. High saturation magnetization （78.3 emu/g）, low coercivity （45 Oe, 10e = 79.5775 A.cm-1）, low remanence （5.32 emu/g）, and high anisotropy constant 2.84 × 10^4 J/m3 （10 times larger than bulk） are observed at room temperatures. The nearly snperparamagnetic behavior is ~ spin due to comparable size of nanospheres with superparamagnetic critical thameter Dcr spm The high value of Keff may be due to coupling between the pinned moment in the amorphous shell and the magnetic moment in the core of the nanospheres. The nanospheres show prominent optical absorption in the visible region, and the indirect band gap is estimated to be 0.98 eV from the transmission spectrum. The prepared Mn ferrite has potential applications in biomedicine and photocatalysis.

Texture and self-biased property of an oriented M-type barium ferrite thick film by tape casting

In this paper, the oriented M-type barium ferrite （BaM） thick films with different thicknesses are prepared by tape casting. It is found that the crystallographic alignment degree （f）, the pore and the squareness ratio （Mr/Ms） are not affected by the thickness of the film. XRD and SEM results show that the thick film has hexagonal morphology with a crystal texture of c-axis grains perpendicular to film plane. The hysteresis curve indicates that the BaM thick film exhibits a self-biased property with a remanent magnetization of 3.30 T, a squareness ratio （Mr/Ms） of 0.81, and a coercivity of 0.40 T. The results show that the BaM thick film has potential for use in self-biasing microwave devices, and also proves that the tape casting technique is capable of fabricating high-quality barium ferrite films, thus providing a unique opportunity to realize the large area production of thick film.

Direct Preparation of the Nanocrystalline MnZn Ferrites by Using Oxalate as Precipitant

Oxalate was generally used as a precipitant for synthesis of MnZn ferrites during the co-precipitation process. However, the MnZn ferrite couldn’t be directly obtained and a calcination process was needed. In this research, we reported a direct preparation of the MnZn ferrite nanoparticles by using co-precipitation method, together with refluxing process. XRD measurements proved that crystallite size of the obtained samples increased with an increase in pH value of the co-precipitation solution, and that the crystallite size of about 25 nm was obtained for the sample at a pH of 13. This sample showed the maximum Ms of 58.6 emu/g, which was about one times larger than that of 12 (pH value). Calcination to the obtained samples result in an enlargement in their crystal size and an improvement in their magnetic properties with an increase in temperatures. The samples calcinated in CO2 + H2 atmosphere presented good stability, and the maximum Ms value of 188.2 emu/g was obtained for the 1100。C-heated sample. Unfortunately, precipitation of some Fe2O3 at 800。C suggested poor stability of the nanocrystalline MnZn ferrite in N2 atmosphere.

Synthesis of Nanocrystalline Barium Ferrite in Ethanol/Water Media

Nanocrystalline particles of barium ferrite magnetic material have been prepared by co-precipitation route using aqueous and non-aqueous solutions of iron and barium chlorides with a Fe/Ba molar ratio of 11 and subsequent drying-annealing treatment. Water and ethanol/water mixture with volume ratio of 3：1 were used as solvents in the process. Coprecipitated powders were annealed at various temperatures for 1 h. FTIR （Fourier transform infrared spectroscopy）, XRD （X-ray diffraction）, DTA/TGA （differential thermal analy- sis/thermogravimetric analysis） and SEM （scanning electron microscopy） techniques were used to evaluate powder particle characteristics. DTA/TGA results confirmed by those obtained from XRD indicated that the formation of barium ferrite occurs in sample synthesized in ethanol/water solution at a relatively low temper- ature of 631℃. Nano-size particles of barium ferrite with mean particle size of almost 75 and 100 nm were observed in the SEM micrographs of the samples synthesized in ethanol/water solution after annealing at 700 and 800℃ for 1 h, respectively.

Synthesis and Properties of Tubular Polyaniline-Barium Ferrite Composite

The polyaniline-barium ferrite composite was synthesized by in situ polymerization of aniline in the presence of BaFe12019 nanoparticles. The structure, morphology, and magnetic properties of samples were characterized by powder X-ray diffraction （XRD）, Fourier transform infrared （FTIR）, scanning electron microscopy （SEM） and vibrating sample magnetometer （VSM）. The testing results showed that the composite exhibited the ferromagnetic and electric behaviors, which benefit for the application of electromagnetic interfence.

Nd-Fe-B永磁体材料的金刚石工具套料加工

对Nd-Fe-B烧结永磁体材料的金刚石工具套料钻削加工进行了比较详细的研究。实验结果表明,在选择合适的进给压力和充分冷却的条件下,应尽量提高金刚石工具的转速,以便获得较高的加工效率、加工精度和加工表面质量。如果套料加工的工件厚度较大,必须认真考虑排屑问题。

Nd-Fe-B烧结永磁体材料的超声加工机理

对Nd-Fe-B烧结永磁体材料超声振动加工过程中的材料去处机理进行了理论研究,研究结果对实际生产具有一定的指导作用,并进行了加工实验研究。

软磁不锈钢环样和棒样磁性能测量结果差异及其机理分析

随着自动控制领域对软磁不锈钢磁性能和综合性能的要求越来越高,软磁不锈钢的磁性能检测变得越来越重要。首先介绍了软磁材料的起始磁化曲线和正常磁化曲线,然后对软磁不锈钢磁性能检测中标准规定的环样法和棒样法(磁导计法)的磁性能测试结果进行比较和分析,对存在差异的原因进行了探讨,并对以后在测量中可能采取的措施进行了介绍。实验证明,环样法和棒样法间磁性能的差异是普遍存在的一种现象。受测试方法的限制,只有采取合理的措施,才能得到供需双方都能认可的测量结果。

隐身纳米吸波材料的研究进展

纳米吸波材料作为武器装备的重要隐身技术,对于提高其作战能力有着重要的作用。本文重点阐述了磁纳米、石墨烯、生物质碳基和碳纳米管等复合材料在吸波领域研究的最新进展,简要总结了不同类型吸波材料对电磁波的吸收机制。

In^(3+)取代对NiZn微波多晶铁氧体材料电磁性能的影响

采用普通陶瓷工艺制备微波多晶尖晶石NiZnIn铁氧体材料,研究了In^(3+)取代对材料微观结构、电磁性能的影响。结果表明,当In^(3+)取代量x在0~0.2范围时,材料的饱和磁化强度4πMs变化很小,气孔率p略有降低,铁磁共振线宽ΔH以各向异性致宽ΔHa为主;当x>0.2后,材料的饱和磁化强度4πMs明显降低,气孔率p增大,铁磁共振线宽ΔH以气孔致宽ΔHp为主。In^(3+)取代NiZn铁氧体使材料的铁磁共振线宽ΔH明显降低,介电损耗角正切tanδε降低至0.5×10^(-4)以下,居里温度近似线性下降。In^(3+)取代NiZn铁氧体烧结温度范围宽,在1200~1240℃温度下烧结,材料的4πMs、ΔH、tanδε变化均较小,工艺实现容易。

Ga^(3+)替代Fe^(3+)对BaW铁氧体纤维微结构和磁性能的影响

本文采用高压静电纺丝法成功合成了BaZn_(2)Fe_(16-x)Ga_(x)O_(27)(x=0.0,0.3,0.6,0.9,1.2,1.5)系列W型铁氧体样品。X射线衍射结果表明所合成系列样品均为纯相,空间群为P63/mmc。扫描电子显微镜结果显示烧结后样品呈六角片状,直径约为10μm,厚度约为2μm。红外光谱测试表明波数420 cm^(-1)和580 cm^(-1)分别对应W型铁氧体八面体位和四面体位的Fe^(3+)-O^(2-)键振动产生的特征吸收峰。磁滞回线显示随着Ga^(3+)替代量x的增加,饱和磁化强度先增大后减小,在x=0.6时达到最大值52.84 emu/g。矫顽力经历了先降低再升高后降低的过程。

微量Co^(2+)-Si^(4+)取代对多晶石榴石铁氧体材料旋矩磁性能的影响

采用传统陶瓷工艺制备了多晶石榴石铁氧体,研究了微量Co^(2+)-Si^(4+)联合取代对GdCaSnV-YIG、GdCaZrV-YIG、GdCaInV-YIG和GdAl-YIG材料旋矩磁性能的影响。结果表明,Co^(2+)-Si^(4+)联合取代GdAl-YIG可使其矫顽力显著增高,而Co^(2+)-Si^(4+)取代GdCaSnV-YIG、GdCaZrV-YIG和GdCaInV-YIG,可调节其矫顽力和剩磁比。当Co^(2+)-Si^(4+)取代量为0.015时得到GdCaSnV-YIG的矫顽力为0.17 Oe,取代量为0.025时得到GdCaZrV-YIG的矫顽力为0.23 Oe,取代量大于等于0.035时三者的剩磁比均能达到0.79或以上。