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H. M. I. Abdallah J. Z. Msomi T. Moyo A. Lan?ok 《Journal of Superconductivity and Novel Magnetism》2012,25(8):2619-2623
We report the magnetic properties of Mn0.5Co0.5Fe2O4 and Mn0.1Mg0.2Co0.7Fe2O4 nanoferrites. The compounds were synthesized by a glycol-thermal method with average particle sizes of about 13?nm and 8?nm, respectively. The M?ssbauer measurements were done at 300?K. The distribution of cations between tetrahedral?(A) and octahedral?(B) sites is investigated. The M?ssbauer spectra indicate ferrimagnetic behavior of the compound. Field cooled (FC) and zero field cooled (ZFC) magnetizations were performed by a Superconducting Quantum Interference Device (SQUID) magnetometer from 4?C380?K. Variation of the magnetizations with the applied fields (up to 50 kOe) were recorded at isothermal temperatures 4, 50, 100, 200 and 300?K. An increase in FC magnetization is observed with increasing applied field. This is explained based on superparamagnetic behavior of the particles. 相似文献
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Jinwen Huang Peng Su Wenwei Wu Bang Liu 《Journal of Superconductivity and Novel Magnetism》2014,27(10):2317-2326
Co0.5Mn0.5La x Fe2?x O4 precursor was synthesized by solid-state reaction at low temperatures using CoSO4 ?7H2O, MnSO4 ?H2O, FeSO4 ?7H2O, La(NO 3)3 ?6H2O, and Na2 CO 3 ?10H2O as raw materials. Co0.5Mn0.5La x Fe2?x O4 was obtained by calcining carbonates precursor in air. The precursor and its calcined products were characterized by thermogravimetry and differential scanning calorimetry, X-ray powder diffraction, scanning electron microscopy, and vibrating sample magnetometer. A high-crystallized Co0.5Mn0.5La x Fe 2?x O4 with a cubic structure was obtained when the precursor was calcined at 700 °C in air for 2 h. The specific saturation magnetizations and coercivity of Co0.5Mn0.5La x Fe2?x O4 depend on the calcination temperature and composition. The thermal transformation of Co0.5Mn0.5CO3–Fe2O3?0.967H2O from 700 °C in air presented two steps. The values of the activation energies associated with the thermal transformation of Mn0.5Co0.5CO3–Fe2O3?0.967H2O were determined based on the Kissinger–Akahira–Sunose (KAS) equation 相似文献
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We analyzed nanostructured Fe60Co40 alloy obtained by mechanical alloying using a planetary ball mill. The prepared powders were characterized using X-ray Diffraction (XRD), Laser particle-measurement, scanning electron microscopy (SEM), X band waveguide and cavity resonator associated with Network analyzer. Obtained results are discussed according to milling time.XRD patterns show after 12 h of milling the formation of a disordered solid solution having body-centerd cubic (bcc) structure. After 36 h milling, morphological studies indicated that the average crystallites size is around 13 nm and the particles average diameter is about 3.6 μm. The microwave absorbing characteristic was enhanced between 0 and 54 h of milling (from ?0.8 to ?13.807 dB) with decreasing in the relative dielectric permittivity εr. 相似文献
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本文采用熔体快淬法制备了纳米微晶Nd8.5Dy0.5Fe84.5Co0.5B6合金,对不同晶化工艺条件下的合金进行了显微组织分析、X射线衍射物相分析和磁性能分析,通过研究该合金的非晶晶化法制备纳米微晶的工艺参数,确定了该材料的最佳晶化工艺:750℃下保温0.5小时,获得平均晶粒尺寸为50nm左右,磁性能优良. 相似文献
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L.F.F.P.G. Bragança R.R. Avillez C.R. Moreira M.I. Pais da Silva 《Materials Chemistry and Physics》2013
Co–Fe bimetallic samples containing 25 wt% total of metal content were prepared by incipient wetness impregnation of cobalt nitrate and iron nitrate salts over hexagonal mesoporous silica (HMS) and SBA-15 supports. Changes in the textural properties and reduction behavior were compared with monometallic cobalt/iron-based samples. The samples were characterized by N2 physisorption, X-ray diffraction (XRD), H2-temperature programmed reduction (TPR), transmission electron microscopy (TEM) and H2 chemisorption. The amount of incorporated metal was estimated by atomic absorption spectroscopy (AAS). Morphological properties revealed that after introduction of the metal to the SBA-15 support, the specific area, pore volume and pore diameter decreased to a lesser extent for bimetallic samples. XRD measurements detected the formation of Co3O4 and CoFe2O4 phases for both bimetallic samples. TPR profiles indicated similar behavior for both the bimetallic and monometallic samples. Higher temperatures were observed for the reducibility of Co–Fe/HMS as compared to Co–Fe/SBA-15. Dispersion values of the bimetallic samples were higher than Fe monometallic samples and lower than Co monometallic samples according to hydrogen chemisorption. The particle size distribution of the bimetallic samples estimated by TEM microphotographs showed a smaller fraction of larger size particles for Co–Fe/SBA-15. 相似文献
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采用传统固相反应法与两步合成法制备了PrBi4Fe0.5Co0.5Ti3O15陶瓷, 研究了Pr与Co共掺杂对Bi5FeTi3O15陶瓷的结构、磁性能以及介电性能的影响。X射线衍射分析显示, 传统固相反应法制备的样品比两步法制备的样品更容易形成单相结构。铁电和磁性测量证明样品具有多铁性, 并且Pr与Co共掺杂能大幅提高材料的磁性能, 固相反应法与两步合成法制备的样品在室温下的剩余磁化强度(2Mr)分别为0.315, 0.576 Am2/kg, 比文献报道的Bi5FeTi3O15陶瓷的2Mr ( 2.7 Am2/kg ) 高5个数量级, 比掺Co的Bi5Fe0.5Co0.5Ti3O15陶瓷2Mr ( 7.8×10-3 Am2/kg ) 高2个数量级。 相似文献
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Caiyin YOU Zhidong ZHANG Xiaokai SUN C.J.Yang Wei LIU Xingguo ZHAO 《材料科学技术学报》2007,23(4):521-524
Exchange interaction plays an important role on magnetic properties of nanocomposite magnets consisting of hard- and soft-magnetic phases. Here the exchange interaction in the Sm-Co/Co (and Fe65Co35) magnetic films was characterized by measuring static (mr(H)) and demagnetized (md(H)) remanence curves. According to conventional method: δm(H)=md(H) - [1 - 2mr(H)], the exchange interaction was evaluated. The switching fields H′p and Hp, at which static (mr(H)) and demagnetized (md(H)) remanence show the fastest change, were identified. The relative ratio η=Hp-H′p/Hp of switching fields H′p and Hp has a linear relationship with the maximum value δmmax of δm(H) curves, proposing an alternative way to characterize the exchange interaction. 相似文献
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《Advanced Powder Technology》2014,25(1):462-466
Fe1−xCox(x = 0.1, 0.15, 0.2, 0.25, 0.3 and 0.5) powders were prepared by different milling-annealing treatments, and magnetic properties were investigated based on microstructure. Elevated heating times led to an increase in crystallite size, and decrease in lattice parameter. Up to 20 min annealing, series 3 powders showed a decrease in microstrain 2.5 times more than series 2. The coercivity (HC) of 1-step milled and 60 min annealed Fe50Co50 alloys decreased rigorously from 60 Oe to 19 Oe due to strain relief (from 0.3% to 0.08%) and grain growth (from 30 nm to 40 nm). For series 2 alloys, the HC (up to 60 min heating) increased from 72 Oe to 90 Oe, and decreased (up to 100 min heating) to 70 Oe. Compared to series 1, extra milling treatment of series 2 causes an increase in magnetization saturation (MS) due to completion of alloying and grain refinement. Also, compared to series 2, extra annealing treatment for series 3 resulted in larger values of MS caused by stain relief. 相似文献
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Structural and various electrical properties of polycrystalline Ca0.05+xNd0.5-x(Ti0.5Fe0.5)O3,prepared by standard solid state reaction technique,were studied.Formation of single phase orthorhombic structure of the compositions was confirmed by X-ray diffraction study.The composition dependence of lattice parameters, density and microstructural study show that they vary significantly with Ca content.The dielectric measurements were carried out at room temperature as function of frequency and composition.The experimental results reveal that the dielectric constant(ε’) increases with increasing Ca content.Similar behavior is observed for the dielectric loss(tanδ) and ac conductivity(σac).In complex impedance analysis it is observed that the real part(Z’) vs imaginary part(Z") graph exhibits a tendency of formation of a single semicircular arc for each composition of samples.Different parameters were determined by fitting the experimental data in Cole—Cole empirical formula.A dominance of grain boundary resistance(Rgb) is observed.The Rgb decreases with increasing Ca content.The highε’ observed in present samples are suitable for fabrication of devices. 相似文献
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《International Journal of Inorganic Materials》1999,1(2):187-192
Structural investigations by X-ray powder diffraction, magnetic measurements and by Mössbauer spectroscopy, applied to a series of solid solutions formed between two mixed spinels, zinc–nickel ferrite and cadmium–nickel ferrite, indicates the difference in the cation arrangement in the solid solution obtained hydrothermally, compared to that of ferrites sintered at high temperatures. The ferrimagnetic crystalline Cd–Zn–Ni ferrite series, of a composition of Cd0.5-αZnαNi0.5Fe2O4, have been prepared by hydrothermal treatment of the coprecipitated amorphous Cd–Zn–Ni–Fe hydroxide mixtures. The hydrothermally obtained samples displaying a defected spinel structure, with clearly noticeable non-stoichiometry, may be considered as precursors for the preparation of stoichiometric products by further thermal treatment. The first approach to the Mössbauer spectra of the system (Cd0.5-αZnαFe0.5)tetr[Ni0.5Fe1.5]octO4 analysis has been undertaken. 相似文献
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《Materials Letters》2004,58(27-28):3564-3568
Iron and carbon powder were co-milled and consolidated. Investigation methods used echography and acoustic microscopy. Grain size, microstructure and mechanical properties were found to depend on milling, heating and alloy initial composition. Consolidated nanocrystalline iron hardness was found a lot lower than in formulated predictions according to results from milled powders using Petch-Hall law. This could be related to heating which reduces internal stresses and defects at grain boundaries. Observed alloys strengthening could be related to cementite precipitates or to synthesized carbide phases, and observed alloys elastic moduli reduction to residual-free carbon. 相似文献
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氢氧根共沉淀法合成了阴极材料Ba0.5Sr0.5Co0.8Fe0.2O3-δ(BSCF).利用XRD、SEM、EDX和DSC/TG等技术研究了前驱体不同温度煅烧后的晶化行为,考察了BSCF材料的电导率和热稳定性能.结果表明,前驱体在1173K下煅烧2h,产物为单一的立方型钙钛矿相结构,粒径在1mm以下;当煅烧温度升至1273K,产物的组成配比为Ba0.48Sr0.52Co0.78Fe0.19O3-δ,但粉末之间发生烧结.空气中,BSCF支撑体的电导率在773~1073K之间均在120S/cm以上.材料在1183K时发生相转变,相变焓为49.47J/g,但材料在673~1273K仍显示了较好的热稳定性. 相似文献
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用共沉淀法合成了具有单一的立方型钙钛矿结构的新型阴极材料Ba0.5Sr0.5Co0.8Fe0.2O3-δ,研究了材料的电导率和热膨胀系数与温度的关系.结果表明,前驱体在1100℃煅烧3 h后形成具有单一的立方型钙钛矿结构尺寸小于1 μm的Ba0.5Sr0.5Co0.8Fe0.2O3-δ粉末;在500~600℃致密材料的电导率高于100 S/cm,热膨胀系数随着温度的升高从13.62×10-6逐渐增大到18.75×10-6,当温度超过700℃后急剧增大.致密材料热膨胀系数在高温下剧增的主要原因是材料中比较大的氧损失. 相似文献
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V.D. Nithya R. Jacob Immanuel S.T. Senthilkumar C. Sanjeeviraja I. Perelshtein D. Zitoun R. Kalai Selvan 《Materials Research Bulletin》2012,47(8):1861-1868
The structural, electrical and magnetic properties of LaCr0.5M0.5O3 (M = Cr3+, Cu2+ and Fe3+) synthesized by a sol–gel technique were studied. The X-ray diffraction pattern shows the structure to be orthorhombic and the size of the particles is around 100 nm as seen from the TEM images. The effects of Cu2+ and Fe3+ on the electrical properties of LaCrO3 were studied using impedance spectroscopy at room temperature (RT). The properties of LaCr0.5Cu0.5O3 were studied over a wide range of temperature from RT to 533 K. A maximum conductivity of 1.7 × 10?3 S cm?1 was observed for LaCr0.5Cu0.5O3 at a measured temperature of 533 K. The impedance spectra indicate a negative temperature coefficient of resistance (NTCR) and also imply the conduction is through bulk of the material. The magnetic studies performed using a SQUID magnetometer interpret the antiferromagnetically ordered LaCrO3 to behave ferromagnetically on the addition of Cu2+ and Fe3+, and the magnetization was found to be enhanced in the LaCr0.5Fe0.5O3. 相似文献
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Wahba Adel Maher Moharam Bahaa Eldeen M. Mahmoud Aya Fayez 《Journal of Materials Science: Materials in Electronics》2021,32(11):14194-14206
Journal of Materials Science: Materials in Electronics - In this work, the impact of nonstoichiometric substitution of Fe3+ cations by Ni2+ ones on the structural and magnetic properties of... 相似文献