Synthesis and Investigation of Electrical Properties of Strontium Metal-Doped Hexaferrite Nanoparticles

Journal of Superconductivity and Novel Magnetism - In the current work cobalt, magnesium and lithium dopant substitution is performed in series of SrFe(12-2x)(Co,Mg,Li)xO19 (for...     

Magneto-Structural Characterization of Strontium Substituted Lead Hexaferrite

In this work, the magnetic and structural properties of the system Pb_1?x Sr _x Fe₁₂O₁₉ (x=0.1,0.3,0.5,0.7 and 0.9) are reported. The samples were prepared by the traditional ceramic method. All the compounds are isostructural with the strontium hexaferrite (SrFe₁₂O₁₉). X-ray powder diffraction was used to carry out the quantitative analysis of phases and to determinate the crystallographic parameters. It was found that the compound consists of only one phase and that the coercivity, remanence and saturation increased with the strontium content. The initial susceptibility was also obtained and results are discussed in terms of the magnetization mechanisms produced by the effect of the substitution on the hexaferrite. Furthermore, Néel temperature measurements indicate a strengthening of the exchange interactions with increasing strontium content.     

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.     

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.     

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%.     

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。     

熔盐合成BaFe12O19六角铁氧体及磁性能研究

以Fe2O3、BaCO3为原料,采用熔盐法合成了BaFe12O19(BaM)六角铁氧体,研究了煅烧温度、反应时间、熔盐添加量R及Fe3+/Ba2+摩尔比对产物物相、显微结构及磁性能的影响.结果表明,熔盐合成BaM的反应温度低于750℃,中间产物为BaFe2O4及BaFe4O7.Fe3+/Ba2+摩尔比在10～11.5可得BaM单相.熔盐添加量R为1～3时,所制BaM颗粒为规则六角片状.Fe3+/Ba2+摩尔比为11.5,煅烧温度为1000℃时制得的BaM的比饱和磁化强度为71.9A.m2/kg,接近其理论值72A.m2/kg.     

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.     

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.     

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.     

含天然产物侧基的取代聚乙炔的合成与性能

将天然产物如氨基酸、甾醇、核苷和糖类引入到取代聚乙炔侧链上,利用共轭多烯主链和功能性侧链的协同作用,聚合物表现出光学活性、液晶、刺激响应性、手性识别、生物相容性等新颖性能,在化学传感、信息储存、光学显示、手性探针、药物传递、组织工程等领域具有潜在的应用价值.文中综述了含天然产物分子侧基的取代聚乙炔衍生物的合成与性能,并...     

Solvothermal Synthesis of Pure SrFe12O19 Hexaferrite Nanoplatelets

Strontium hexagonal ferrite, SrFe₁₂O₁₉, with platelet-like structure was synthesized directly by hydrothermal method without any calcination process. The product was characterized by Scanning electron (SEM), X-ray powder diffraction (XRD), Fouier transform infrared spectroscopy (FT-IR), and vibrating sample magnetometry (VSM) techniques. The optimum Fe/Sr moler atio is identified as 8:1, and the optimum weight of NaOH was 4.0 g for the synthesis of the Flake-like SrFe₁₂O₁₉ nanoparticles. The average crystallite size of the product was calculated as 28±5 nm. The low coercivities of the synthesized platelet crystals indicate soft magnetic behavior, which is a consequence of the large shape anisotropy (the platelet crystals are highly anisotropic). The reduced Ms can be explained by increasing surface area of the platelets.     

Synthesis and Characterization of Nano-crystalline Calcium Hexaferrite Particles by Mechano-Thermal Method

Calcium hexaferrite was synthesized using high-energy planetary ball milling of a mixture of CaCO₃ and Fe₂O₃ powders for 10 hours followed by calcination at 1175 ^°C for 1 h. Effects of Fe₂O₃/CaCO₃ molar ratio, mechanical activation and dopant addition on the phase evolution, morphology, and magnetic properties of the products were studied. X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM) technique equipped with an energy dispersive spectrometer (EDS), and vibrating sample magnetometer (VSM). XRD results showed that addition of La₂O₃ in the samples lead to the formation of stabilized calcium hexaferrite particles with a mean crystallite size of 54 nm. Moreover, the formation of calcium hexaferrite was acknowledged at Fe₂O₃/CaCO₃ molar ratio of 5. SEM micrographs showed agglomerated particles of calcium hexaferrite with a mean particle size of 1.5 μm. Nano-crystalline Ca_0.8La_0.2Fe₁₂O₁₆ particles show saturation magnetization of 14 emu/g and coercivity of 500 Oe.     

Preparation and Magnetic Properties of La-Substituted Strontium Hexaferrite by Microwave-Assisted Sol-Gel Method

Sr_1?x La _x Fe₁₂O₁₉ (x = 0, 0.15, 0.25, 0.5) hexaferrites were prepared by microwave-assisted sol-gel method. The thermal decomposition process, structural, and magnetic properties of the products were studied by thermal differential scanning calorimeter (DSC), thermogravimetry (TG), X-ray diffraction (XRD), and vibrating sample magnetometer (VSM). The phase of α-Fe₂O₃ appeared at x = 0.25 and x = 0.5. The coercivity of La³⁺-substituted strontium hexaferrites is improved to 5960.2 Oe at x = 0.25.     

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.     

Ferromagnetic Resonance Investigation of Hexaferrite Nanoparticles Prepared by Sol-Gel Auto-Combustion Method

In this study, the magnetic and electromagnetic wave-absorbing properties of barium and strontium ferrite nanopowders prepared by a sol-gel technique were investigated. To study the structural characteristics of hexaferrites, X-ray diffraction analysis was used. Investigation of the morphologies of nanoparticles was carried out by field emission scanning electron microscopy. A vibrating sample magnetometer was used in order to examine the magnetic properties of synthesized hexaferrites at room temperature. Ferromagnetic resonance (FMR) was used to investigate ferromagnetic resonance of the powders. Experimental results indicated that the materials had hexagonal structures with desirable magnetic properties. A low-field absorption signal was observed with the same phase as the FMR absorption in barium hexaferrites.     

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.     

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.     

低铁磁共振线宽BaFe12O19六角铁氧体的制备及其性能

本研究通过磁场成型技术制备高取向度、高剩磁比的BaFe12O19六角铁氧体;研究助烧剂对BaFe12O19六角铁氧体剩磁比、矫顽力、气孔率及铁磁共振线宽的影响;通过铁磁共振线宽测试,分析各向异性致宽、气孔致宽对铁磁共振线宽的贡献.测试结果表明,样品的最优剩磁比为0.87,铁磁共振线宽为220 Oe.分析结果表明,铁磁共振线宽主要来源于气孔致宽,且磁场成型技术和助烧剂都有利于降低材料的铁磁共振线宽.     

Hydrothermal Synthesis,Structural and Electrical Properties of Antimony (Sb3+) Substituted Nickel Ferrites

Antimony (Sb³⁺) doped nickel ferrites have been synthesized by hydrothermal route using an autoclave at 160 ^°C for 12 hours. Pure spinel phase NiSb _x Fe_2?x O₄ (x=0.0 to 0.1) with step increment of 0.035 has been prepared by sintering the precursor samples at 500 ^°C. Structural studies have been performed using X-ray Diffraction (XRD) and Fourier Transform Infrared Spectroscopy (FTIR). Lattice parameter and X-ray density found to increase with increase in the antimony concentration. Average crystallite size lies in the range of 14 to 24 nm?±?2 nm. Scanning Electron Microscopy (SEM) and Atomic Force Microscopy (AFM) have been used to characterize the morphology and sizes of nanoparticles. Electrical properties were analyzed by measuring DC-electrical resistivity, complex dielectric permittivity, AC conductivity and complex electrical modulus analysis. DC resistivity of nickel ferrites decreases due to the substitution of antimony from 6.7×10⁸ to 3.4×10⁷ Ω-cm. Dielectric permittivity and losses were studied in the frequency range of 20 Hz–5 MHz and found to increase due to addition of Sb³⁺ in nickel nanoferrites at room temperature. High dielectric permittivity and conductivity made this material a compatible option for single-layered and multilayered chip inductors.