Influence of citric acid on the morphology and magnetic properties of barium ferrite thin films

Hexagonal barium ferrite (BaFe₁₂O₁₉) thin films were fabricated by spin coating of precursors from sol-gel methods. Different amount of citric acid was added. Weight loss and changes of chemical bonds during the heat treatment below 500 °C were recorded by thermogravity analyzer and Fourier transform infrared spectroscopy, respectively. The morphology of the films, i.e. the amount of acicular crystallites in the film, was controlled by adjusting the quantity of citric acid. The X-ray diffraction shows that the films are c-axis oriented, but the crystallization is less perfect with the increase of the citric acid. With the increase of the citric acid, the percentage of the acicular crystallites increased. At the same time, the coercivity force increased. The acicular crystallites were not exchange-coupled to the platelet crystallites. The citric acid was understood to form complex with iron ions and accelerate the exothermal auto-combustion. The c-axis oriented growth of the film was thus deteriorated.     

换能器辐射阻抗变化对匹配层参数的影响

匹配层换能器在实用中往往由于辐射阻抗的变化破坏了“最佳”匹配层参量的选取[1]。本文从反映阻抗概念给出了必要的匹配层厚度修正[2],并以实例计算证明了修正公式的实用意义。     

The structural and magnetic powders prepared by properties of barium ferrite the sol-gel method

In this paper,M-type hexagonal barium ferrite powders are synthesized using the sol-gel method.A dried precursor heated in air is analyzed in the temperature range from 50 to 1200 C using thermo-gravimetric analysis and differential scanning calorimetry.The effects of the additives and the cacinating temperature on the magnetic properties are investigated,and the results show that single-phase barium ferrite powders can be formed.After heat-treating at 950 C for 4h with 3 wt% additive,the coercivity and saturation magnetization are found to be 440 Oe and 57.9 emu/g,respectively.     

The structural and magnetic properties of barium ferrite powders prepared by the solben gel method

In this paper, M-type hexagonal barium ferrite powders are synthesized using the sol-gel method. A dried precursor heated in air is analyzed in the temperature range from 50 to 1200 ℃ using thermo-gravimetric analysis and differential scanning calorimetry. The effects of the additives and the cacinating temperature on the magnetic properties are investigated, and the results show that single-phase barium ferrite powders can be formed. After heat-treating at 950 ℃ for 4h with 3 wt% additive, the coercivity and saturation magnetization are found to be 440 Oe and 57.9 emu/g, respectively.     

Efficiency and purity control in the preparation of pure and/or aluminum-doped barium ferrites by hydrothermal methods using ferrous ions as reactants

The synthesis of hexagonal barium ferrite (BaFe₁₂O₁₉) was studied under hydrothermal conditions by a method in which a significant amount of ferrous chloride was introduced alongside ferric chloride among the starting materials. Though all of the Fe²⁺ ions in the starting material were converted to Fe³⁺ ions in the final product, Fe²⁺ was confirmed to participate differently from the Fe³⁺ used in the conventional method in the mechanism of forming barium ferrite. Indeed the efficiency of the synthesis and the quality of the product and the lack of impurities such as Fe₂O₃ and BaFe₂O₄ were improved when Fe²⁺ was included. However, the amount of ferrous ions that could be included to obtain the desired product was limited with an optimum ratio of 2:8 for FeCl₂/FeCl₃ when only 2 h of reaction time were needed. It was also found that the role of trivalent Fe³⁺ could be successfully replaced by Al³⁺. Up to 50% of the iron could be replaced by Al³⁺ in the reactants to produce Al-doped products. It was also found that the ratio of Fe²⁺/M³⁺ could be increased in the presence of Al³⁺ to produce high quality barium ferrite.     

纸质胶带胶层厚度在线测量

在纸质胶带生产过程中 ,胶层厚度及均匀性是很重要的技术指标 ,因此需要对胶层厚度进行在线测量。介绍了一种红外纸质胶带胶层厚度测量仪。它是依据胶质对一定波长的红外光具有特征吸收的原理 ,采用了能量比参考平衡技术 ,使仪器性能稳定、可靠     

First order reversal curves analysis of the temperature effect on magnetic interactions in barium ferrite with La–Co addition

First order reversal curves (FORCs) distributions are a powerful tool for investigating hysteresis and interactions in magnetic systems and have been widely applied. La–Co substitution in barium hexaferrites has also been extensively studied. The most effective substitution to improve the magnetic properties (coercive field and energy product) is given by x=y=0.2 in the formula Ba_1-xLa_xFe_12-yCo_yO₁₉. In this work, this stoichiometry is initially used to obtain a state where more than one phase is present. The magnetic behavior as a function of temperature was studied in order to have an insight into the magnetic interactions that originate a decrease in the magnetic performance of Ba hexaferrite magnets. The sample was structurally characterized by X-ray diffraction (XRD) and magnetically studied in a SQUID magnetometer. FORC distributions were used to study the dependence of the magnetic interactions with the temperature. FORC diagrams performed on the sample at different temperatures exhibit similar characteristics, such as the spread in the h_c–h_u plane and a spread out of the h_c-axes. These features are interpreted in terms of exchange-interacting particles and dipolar interactions, respectively. As the temperature decreases, stronger interactions are noticed among hard and soft phases.     

Effect of doping MnO2 on magnetic properties for M-type barium ferrite

The crystalline structure and magnetic properties of M-type barium ferrite doped with small amounts of MnO₂ (0, 0.25, 0.5, 0.75, 1.0, 1.5, and 2.0 wt%, respectively) have been investigated by means of XRD, SEM and VSM. The results show that the crystalline structures of barium ferrite are still M-type hexagonal structure and Mn ions are distributed homogeneously in both the grains and the grain boundaries. The saturation magnetization and magnetocrystalline anisotropy constants both reach the highest values when x=0.75 wt%. The displacement of Fe ions from 4f₁ to 2b site is mainly responsible for the appearance of the maximum values.     

The structural properties of Al doped ZnO films depending on the thickness and their effect on the electrical properties

In this study, the structural and electrical properties of AZO films with different film thickness deposited by r.f. magnetron sputtering were interpreted in relation with film growth process. The result shows that the grain size increases during film growth, which is accompanied by decrease of compressive stress, indicating the enhancement of crystallinity. The relationship between grain size and compressive stress follows the same tendency for the samples regardless of deposition temperature, which implies the strong dependencies between the grain size and the compressive stress. The XPS analysis shows that the defects such as chemisorbed oxygen and segregated Al₂O₃ cluster at grain boundary are reduced with increase of film thickness or deposition temperature, leading to increase of carrier concentration and mobility. The mobility increase is accompanied by grain size increase and compressive stress reduction, indicating the influences of grain boundary and crystallinity on the mobility.     

The influence of impurity on the critical thickness of the CeO_2 buffer layer for coated conductors

The lattice parameters, band structure, density of state and elastic constant of RE-doped CeO2 (RE=Sm, Gd, Dy), the buffer material for coated HTS conductors, are calculated using the plane-wave method with pseudopotentials based on the density functional theory (DFT) of first-principle. The rule and mechanism of the effect of rare earth impurity on the critical thickness of the CeO2 buffer layer are investigated. It is found that, in the range of the calculation, the changes of the lattice volume V and ela...     

Preparation, characterization and magnetic properties of the doped barium hexaferrites BaFe12−2xCox/2Znx/2SnxO19, x=0.0-2.0

A series of powders of M-typed barium hexaferrites doped with Co, Zn and Sn of general formula BaFe_12-2xCo_x/2Zn_x/2Sn_xO₁₉ (x=0-2.0) were prepared by the co-precipitation/molten salt method. The structures, particle morphology and magnetic properties of the products were characterized by X-ray powder diffraction, vibrating sample magnetometer and ESEM/EDX. The results show that the crystallinity of the samples decreases with increase in the doping amount x. When x is less than 0.6, it is possible to obtain perfectly crystallized hexagonal BaFe_12-2xCo_x/2Zn_x/2Sn_xO₁₉, where the diameters of the particles are around 500 nm. The saturation magnetization of pure barium ferrite BaFe₁₂O₁₉ produced with this method is 71.9 A m² kg⁻¹ at room temperature and the intrinsic coercivity (H_c) is 367.8 kA m⁻¹. The doped barium hexaferrite powder obtained when x is between 0.3 and 0.4 exhibits high saturation magnetization and a temperature dependence of coercivity close to zero.     

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采用三支节液态调配器使离子回旋加热(ICRH)天线系统达到阻抗匹配,在阻抗匹配的条件下结合频率调制技术来减小由天线输入阻抗变化所引起的反射功率。数值模拟了频率调制前后天线负载与反射系数的变化关系,用来验证频率调制对ICRH天线中阻抗匹配装置的影响。模拟结果表明:三支节液态调配器结合频率调制方法,能更好地降低天线传输系统的反射系数,使得发射机的功率通过天线辐射更加有效地耦合到等离子体中去。     

Studies on the activation energy from the ac conductivity measurements of rubber ferrite composites containing manganese zinc ferrite

Manganese zinc ferrites (MZF) have resistivities between 0.01 and 10 Ω m. Making composite materials of ferrites with either natural rubber or plastics will modify the electrical properties of ferrites. The moldability and flexibility of these composites find wide use in industrial and other scientific applications. Mixed ferrites belonging to the series Mn_(1−x)Zn_xFe₂O₄ were synthesized for different ‘x’ values in steps of 0.2, and incorporated in natural rubber matrix (RFC). From the dielectric measurements of the ceramic manganese zinc ferrite and rubber ferrite composites, ac conductivity and activation energy were evaluated. A program was developed with the aid of the LabVIEW package to automate the measurements. The ac conductivity of RFC was then correlated with that of the magnetic filler and matrix by a mixture equation which helps to tailor properties of these composites.     

Effect of Mg substitution on the magnetic properties of NiCuZn ferrite nanoparticles prepared through a novel method using egg white

Nanocrystalline Mg-substituted NiCuZn ferrites were successfully synthesized, for the first time, by using metal nitrates and freshly extracted egg white. The thermal decomposition process of the nitrate-egg white precursors was investigated by thermogravimetric (TG) technique. X-ray diffraction (XRD) revealed that, single-phase cubic ferrites with average particle size of 23.9-35.1 nm were directly formed after ignition at 500 °C. No noticeable variation of lattice parameters with increasing magnesium content was observed, while X-ray densities were found to decrease. This can be explained on the basis of ionic radii and atomic masses of the substituted cation. Transmission electron microscope (TEM) shows that, particles are permanently magnetized and get agglomerated. The saturation magnetization (M_s) and coercivity (H_c) as a function of Mg content were investigated using vibrating sample magnetometer (VSM). It has been found that the M_s increases firstly up to x=0.2 and then decreases, while H_c continuously decreases. Magnetic susceptibility measurements give results which agree well with those obtained by VSM. The obvious decrease in the Curie temperature (T_C) with increasing Mg indicates that the ferrimagnetic grains are widely separated and enclosed by non-magnetic magnesium ions.     

Influence of layer thickness on the structure and the magnetic properties of Co/Pd epitaxial multilayer films

Co/Pd epitaxial multilayer films were prepared on Pd(111)_fcc underlayers hetero-epitaxially grown on MgO(111)_B1 single-crystal substrates at room temperature by ultra-high vacuum RF magnetron sputtering. In-situ reflection high energy electron diffraction shows that the in-plane lattice spacing of Co on Pd layer gradually decreases with increasing the Co layer thickness, whereas that of Pd on Co layer remains unchanged during the Pd layer formation. The CoPd alloy phase formation is observed around the Co/Pd interface. The atomic mixing is enhanced for thinner Co and Pd layers in multilayer structure. With decreasing the Co and the Pd layer thicknesses and increasing the repetition number of Co/Pd multilayer film, stronger perpendicular magnetic anisotropy is observed. The relationships between the film structure and the magnetic properties are discussed.     

The influence of impurity on the critical thickness of the CeO<Subscript>2</Subscript> buffer layer for coated conductors

The lattice parameters, band structure, density of state and elastic constant of RE-doped CeO₂ (RE=Sm, Gd, Dy), the buffer material for coated HTS conductors, are calculated using the plane-wave method with pseudopotentials based on the density functional theory (DFT) of first-principle. The rule and mechanism of the effect of rare earth impurity on the critical thickness of the CeO₂ buffer layer are investigated. It is found that, in the range of the calculation, the changes of the lattice volume V and elastic constant E* of CeO₂ with the impurity are mainly determined by the increased electrons δn _e of the system. The relationship of the elastic constant E* and increased electrons δn _e is established. It is indicated that the critical thickness of the CeO₂ single buffer layer doped with Sm, Gd, and Dy may be enhanced by 22%, 43% and 33%, respectively. Supported by the Youth Scientific Research Project of Southwest Jiaotong University (Grant No. 2007Q017), the National Natural Science Foundation of China (Grant No. 50588201), and the Ministry of Science and Technology of China (Grant No. 2007CB616906)     

Cobalt ferrite nanoparticles: The control of the particle size and surface state and their effects on magnetic properties

In order to improve the efficacy of magnetic fluid hyperthermia (MFH) mediators, we synthesised cobalt ferrite nanoparticles with different sizes (between 5 and 7 nm) via successive polyol synthesis. The static and dynamic magnetic properties of the prepared particles, dispersed in a solid matrix, were investigated in order to evaluate the possibility of applying cobalt ferrite as magnetic susceptors in MFH. The effect on magnetic properties coming from the surface anchoring of the model molecule cetyl phosphate, was also investigated.     

Effect of aluminum substitution on the structural and magnetic properties of cobalt ferrite synthesized by sol-gel auto combustion process

Aluminum substituted cobalt ferrite powders (CoFe_2−xAl_xO₄) with varying composition from 0.0 to 1.0 in the step of 0.2 have been obtained by sol-gel auto combustion technique using citric acid as a fuel. The metal nitrate to fuel ratio was maintained 1:4 throughout the synthesis of CoFe_2−xAl_xO₄. The thermal analysis of as prepared samples is done by TGA technique. The compositional stoichiometry of the prepared samples is confirmed by Energy dispersive X-ray analysis technique. Single phase cubic spinel structure and nano phase structure of the synthesized powders were confirmed by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The crystallite size of 16-26 nm was obtained using Scherrer formula. SEM analysis shows the formation of uniform grain growth. The grain size obtained from SEM results is of the order of 30 nm. Maximum specific surface area was observed to be of the order of 52 m²/gm. The highest value of saturation magnetization and coercivity was observed for pure cobalt ferrite sample and it decreases as the aluminum content x increases. A strong co-relation between the saturation magnetization and aluminum content was observed. The decrease in magnetic properties is due to the substitution of aluminum ions in place of Fe³⁺.