Effect of Barium on the Properties of Lead Hexaferrite

An analysis of the properties of a family based on lead-barium substitution in the M-type hexaferrite is presented. The samples were prepared by the ceramic method according to the general formula Pb _x Ba_1?x Fe₁₂O₁₉. The barium content was varied with x=0.1, 0.3, 0.5, 0.7, and 0.9; no secondary phases were detected in any composition. Rietveld refinement analysis was done in order to determinate crystallographic parameters, content of phases and degree of substitution. The effects of the barium on the morphological and magnetic properties were studied. Iron Mössbauer spectroscopy was used for determining the hyperfine parameters of the iron nucleus and their environment; also, the cationic occupancy was evaluated and the results were checked with X-ray refinement results.     

Effect of Microwave Processing on Polycrystalline Hard Barium Hexaferrite

The present paper describes our results on the phase transformation (from crystalline to amorphous) of M-type hard barium hexaferrite, and consequently its conversion into soft ferrite by the application of magnetic energy at microwave frequency (2.45 GHz). The rapid volumetric heating of the conventionally prepared polycrystalline hexaferrite by microwave energy at a temperature of 950?°C in a short duration of only 5 min resulted in a decrystallized phase. The magnetic studies (M?CH loops) of the resistively heated and MW processed samples have revealed a lowering in coercivity (from 188 to 2 mT) in the latter samples, thereby establishing the formation of soft ferrite. An attempt has also been made to understand the observed transformation from hard to soft ferrite.     

Microwave Charecterization of Co-Doped Barium Hexaferrite Absorber Metarial

Co-doped BaFe₁₁CoO₁₉ barium hexaferrites were prepared with the standard sintering technique generally used for microwave absorber materials. In this work, XRD was used to identify the structure of the synthesized sample, vibrating sample magnetometer was used to obtain magnetic hysteresis loop of sample, and scanning electron microscopy was used to study its surface morphology. The complex permeability and complex permittivity were measured with an automated commercial measurement set up in the 18–26.5-GHz frequency range using the Nicolson-Ross-Weir (NRW) method. A domain wall resonance was detected around 19 GHz, and the maximum reflection loss value in the domain wall resonance region was found to be 18.3 dB, the minimum reflection loss value was found to be 14.5 dB. Co-doped BaFe₁₁CoO₁₉ barium hexaferrites seem to be a good candidate as a microwave absorber. The synthesis procedure and the measurement results are presented below.     

Modeling of Magnetic Properties of Nanocrystalline La-doped Barium Hexaferrite

In this paper an artificial neural network (ANN) has been developed to compute the magnetization of the pure and La-doped barium ferrite powders synthesized in ammonium nitrate melt. The input parameters were: the Fe/Ba ratio, La content, sintering temperature, HCl washing and applied magnetic field. A total of 8284 input data set from currently measured 35 different samples with different Fe/Ba ratios, La contents and washed or not washed in HCl were available. These data were used in the training set for the multilayer perceptron (MLP) neural network trained by Levenberg–Marquardt learning algorithm. The hyperbolic tangent and sigmoid transfer functions were used in the hidden layer and output layer, respectively. The correlation coefficients for the magnetization were found to be 0.9999 after the network was trained.     

单相钡铁氧体磁性材料的制备及磁性能研究

以硝酸钡、硝酸铁和柠檬酸为原料,采用溶胶-凝胶法制备了单相钡铁氧体(BaFe12O19)纳米粉体,并进一步研究了n(Fe)/n(Ba)、热处理温度对产物组成、形貌以及磁性能的影响。用X射线衍射仪(XRD)、扫描电子显微镜(SEM)和振动样品磁强计(VSM)分别对样品的组成、形貌和磁性能进行了表征。实验结果表明,当煅烧温度不变时,样品的晶粒尺寸随着n(Fe)/n(Ba)的增大而变大,磁性能随n(Fe)/n(Ba)的增大而增强;当n(Fe)/n(Ba)不变时,样品的晶粒尺寸随着煅烧温度的升高而变大。当n(Fe)/n(Ba)=12时,在800℃煅烧2h得到单一晶型的钡铁氧体粉体。1000℃时样品的磁性能最佳,饱和磁化强度(Ms)为70.88A.m2/kg,矫顽力(Hc)为372.89kA/m。     

Collapse of the Magnetic Hyperfine Structure of Barium Hexaferrite by Mechanochemical Activation

The collapse of the magnetic hyperfine structure of barium hexaferrite as an effect of mechanochemical activation was investigated. The various inequivalent sites and phases present in the milled material were studied by transmission Mössbauer spectroscopy. Barium hexaferrite nanoparticles were obtained after only 2 h of milling time and were found to coexist with iron oxide particles for longer times of exposure to mechanochemical activation. The milled samples were then subjected to thermal annealing, in order to test the reversibility of the collapse of the hyperfine structure. The thermal annealing performed (700°C, 1 h) was partly successful in restoring the magnetic hyperfine structure of milled hexaferrite. Complementary information was obtained using transmission electron microscopy (TEM) and electron diffraction (ED).     

Structural, Magnetic and Microwave Properties of Eu-doped Barium Hexaferrite Powders

Eu-doped M-type barium ferrite powders (Ba_1−x Eu _x Fe₁₂O₁₉) with x=0.0, 0.1, 0.2 and 0.25 were prepared by sol-gel method. The synthesized samples are characterized by thermo gravimetric analysis (TG-DTA), X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, scanning electron microscopy (SEM), vibrating sample magnetometer (VSM) and vector network analyzer. All the synthesized samples have the nearly single-magnetoplumbite phase. The results show that the crystallite size of doped samples is smaller than pure one. The saturation magnetization of doped ferrites decreases by the increase in Eu doping, while the coercivity increases. Maximum coercivity achieved in this study is 6.12 KOe for x=0.25 sample. The enhancement of coercivity by Eu doping is mainly due to the higher magnetocrystalline anisotropy, which is attributed to the partial change of Fe⁺³ ion to Fe⁺² ion. The maximum reflection loss (RL) of −43 dB at frequency range of 12–18 GHz for the x=0.1 sample was obtained. The increase in reflection loss at higher frequency suggests that the Eu-doped sample can be used for the application in microwave devices.     

工业产品制备纳米级钡铁氧体及其微波性能的研究

以相对分析纯试剂杂质含量较高、价格较低的工业级产品为原料,利用柠檬酸溶胶-凝胶法合成了六角晶系M型钡铁氧体,采用XRD、原子力显微镜对其晶型、粒径分布及显微结构进行了研究,并与分析纯试剂制备的纳米钡铁氧体进行了对比,利用网络分析仪在1～6GHz范围对铁氧体的微波性能进行了分析,结果表明:实验制得粉体为纯净的M型钡铁氧体,其粒度在60nm左右,所含杂质对工艺没有影响,可以用该原料代替分析纯试剂进行制备,并且实验所制备的纳米M型钡铁氧体具有较大的介电损耗和磁损耗,在磁导率虚部随频率变化曲线上出现了一个由自然共振引起的共振吸收峰.     

The Effect of Condensation on the Morphology and Magnetic Properties of Modified Barium Hexaferrite (BaFe12O19)

Nano-Micro Letters - We present a comparison for the effect of condensation on the morphology and magnetic properties of oleic acid modified BaFe12O19 nanoparticles. Two different samples of...     

Synthesis and Magnetic Properties of Barium Hexaferrite Powders Using Organic Acid Precursor Method

An investigation of the synthesis of BaFe₁₂O₁₉ powders by the organic acid precursor method is reported by acidic and neutral media. X-ray diffraction (XRD), scanning electron microscopy (SEM), and vibrating sample magnetometer (VSM) are utilized to study the effect of organic precursor type and annealing temperature on the crystal structure, crystallite size, microstructure and magnetic properties of the formed powders. The XRD analysis showed that the crystalline BaFe₁₂O₁₉ phase was obtained at 1200 °C for 2 h using different carboxylic acids in acidic medium. However, pure BaFe₁₂O₁₉ was achieved at low annealing temperature 1000 °C in neutral medium. SEM micrographs showed that the particles were strongly influenced by type of carboxylic acid and the annealing temperature. VSM study indicated that the saturation magnetization was increased with increasing annealing temperature to 1200 °C as the result of formation of single barium hexaferrites phase. High saturation magnetization (M _s =66.5 emu/g) was achieved for the formed powders in neutral medium using tartaric acid as organic precursor. Wide coercivities of the formed powders (H _c =259–5114 Oe) were obtained.     

钡过量非化学计量M型铁氧体的合成与表征

采用并加共沉淀工艺在900℃热处理2h的条件下合成了单相钡过量非化学计量M型铁氧体Ba_1+xCoTiFe₁₀O_19+x(x=0.00、0.05、0.10、0.15、0.20), 并用XRD、SEM、TEM和VSM表征了这种新的非化学计量M型铁氧体的结构和磁学特性. 结果表明: 当0c和剩余磁化强度σ_r均随x增大而显著增大(Δσ_r=5.36A·m^2·kg^-1, ΔH_c=16.99 kA·m^-1, 但比饱和磁化强度σ_s基本不变; 0.053+离子被稀释导致σ_s、H_c和σ_r均随x增大而持续降低. 同时证实钡过量并不会导致晶体对称性破坏, 02+离子分布于平行于a轴方向的大孔隙位?置, 不仅具有助熔剂作用, 而且对磁畴壁产生了钉扎效应.     

W型钡铁氧体的溶胶-凝胶法制备及吸波性能研究

利用溶胶-凝胶法制备了W型BaZn1.5Co0.5Fe16O27钡铁氧体.在1000℃得到了单一W相纳米晶,晶粒大小为38nm,在1100℃完全形成了大小均匀的平面六角片状结构,其长度为1～3μm,横向尺寸为143～286nm.对其吸波性能进行了测量,发现有2个强吸收峰:0.9GHz和2.4GHz.吸收性能随烧结温度的升高而下降,在0.9GHz的能量吸收率:1000℃为68%,1100℃为48%;在2.4GHz的能量吸收率:1000℃为94%,1100℃为88%.     

二价铁过量M型钡铁氧体的放电等离子体烧结合成

在氩气保护下用化学共沉淀工艺制备了名义组成为BaFe³⁺_11.8Fe²⁺_0.3O₁₉的Fe²⁺过量M型钡铁氧体（BaM）前驱体,采用XRD、SEM和Archimedes法研究了前驱体在放电等离子体烧结（SPS）条件下的物相组成、显微结构和致密度. 结果表明,合成高致密度的单相Fe²⁺过量BaM材料的优化SPS工艺为850℃、保温30min和压力10MPa,其结晶机制为低温下前驱体分解形成α-Fe₂O₃和Fe₃O₄或γ-Fe₂O₃,高温下Fe²⁺过量BaM结晶,整个结晶过程中没有BaFe₂O₄中间相形成. 单相Fe²⁺过量BaM材料的饱和磁化强度为58.2A·m²·kg^-1,矫顽力为255kA·m^-1, 说明Fe²⁺占据自旋向上的2a磁晶位.     

微波辅助溶胶凝胶自燃烧一步合成六角铁酸钡纳米晶及其磁性能

以乙二胺四乙酸柠檬酸+乙二醇为复合络合剂, 冷冻干燥去除溶胶中水分, 提高凝胶中金属离子与氧化剂的分布均匀性, 并利用微波辅助溶胶凝胶自燃烧一步合成了六角铁酸钡纳米晶. 所得纳米晶近于球形, 尺寸在50~100nm, 其饱和磁化强度为338.5kA/m, 矫顽场仅为20.7kA/m. 分析表明, 富氧条件有利于避免自燃烧过程中由于有机物还原引起的铁元素分布不均匀, 从而有利于铁酸钡的相形成.     

Influence of Al Substitution on Structural,Dielectric and Magnetic Properties of M-type Barium Hexaferrite

Polycrystalline Al-substituted BaFe₁₂O₁₉ samples were synthesized and investigated in order to study their structural, dielectric, and magnetic properties. Analysis of powder X-ray diffractions by Rietveld refinement shows the single-phase nature of samples with hexagonal structure. The magnetic properties of the samples were investigated by measuring temperature and field variations of magnetization using vibrating sample magnetometer. The temperature variation of magnetization measurement shows that all samples exhibit ferrimagnetic transition, and the transition temperature is found to decrease from 720 K for x = 0 to 709 K for x = 0.08. The saturation magnetization value at room temperature is found to decrease with increase in Al concentration, and on the other hand, the coercivity is found to increase. The dielectric spectrum of pure and Al-doped samples shows the typical exponential fall in dielectric constant with increase in frequency. The magnitude of dielectric constant at 100 Hz falls from 2000 for x = 0 to 400 for x = 0.10. The permeability spectrum of Al-doped samples is found to be almost independent of frequency for f>100 MHz.     

Nonvolatile Memory via Spin Polaron Formation

A nonvolatile memory is explored theoretically by utilizing the magnetic exchange interaction between localized holes and an adjacent ferromagnetic (FM) material. The active device consists of a buried semiconductor quantum dot (QD) and an FM insulating layer that share an interface. The hole population in the QD is controlled by particle transfer with a reservoir of itinerant holes over a permeable barrier. A theoretical model based on the free energy calculation demonstrates the existence of a bistable state through the mechanism of a collective spin polaron, whose formation and dissolution can be manipulated electrically via a gate bias pulse. The parameter space window suitable for bistability is examined along with the conditions that support maximum nonvolatility. The limitation of QD size scaling is analyzed in terms of the bit retention time.      

Synthesis and Study of the Lanthanum Substitution in the Lead M-Type Hexaferrite

In this work we investigated the best conditions to obtain the lanthanum-substituted lead M-type hexaferrite using the ceramic method. In order to survey the solubility of lanthanum in the structure of the hexaferrite, we varied the molar fraction from 0.1 to 0.9. We performed a structural characterization using X-ray diffraction and used the Rietveld method to refine the crystal structure. The magnetic properties were obtained using vibrating sample magnetometry, and the microstructural characteristics were analyzed using scanning electron microscopy. The results indicate that the crystal structure of the hexaferrite is preserved with a substitution up to 70 %?mol of lanthanum. Moreover, the magnetic characterization exhibits a complicated behavior of parameters when lanthanum concentration increases, which can be attributed to the change of valence state of some iron cations that arises from lanthanum substitution in the hexaferrite; even more, the coercivity presents a drastic fall leading to consider these hexagonal ferrites as magnetically soft.     

Investigations and Correlations of Structural,Magnetic, and Dielectric Properties of M-Type Barium Hexaferrite (BaFe12O19) for Hard Magnet Applications

Journal of Superconductivity and Novel Magnetism - Barium hexaferrite is an essential, prudent, and promising material for the permanent magnet, ceramic, and modernized magnet industry. In the...