M?ssbauer and Magnetic Studies of Co0.5Mn0.5Fe2O4 and Mn0.1Mg0.2Co0.7 Fe2O4 Nanoferrites

We report the magnetic properties of Mn_0.5Co_0.5Fe₂O₄ and Mn_0.1Mg_0.2Co_0.7Fe₂O₄ 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.     

Co0.5Mn0.5La x Fe 2−x O4 Magnetic Particles: Preparation and Kinetics Research of Thermal Transformationof the Precursor

Co_0.5Mn_0.5La _x Fe_2?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. Co_0.5Mn_0.5La _x Fe_2?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 Co_0.5Mn_0.5La _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 Co_0.5Mn_0.5La _x Fe_2?x O₄ depend on the calcination temperature and composition. The thermal transformation of Co_0.5Mn_0.5CO₃–Fe₂O₃?0.967H₂O from 700 °C in air presented two steps. The values of the activation energies associated with the thermal transformation of Mn_0.5Co_0.5CO₃–Fe₂O₃?0.967H₂O were determined based on the Kissinger–Akahira–Sunose (KAS) equation     

Structural and microwave absorption properties of nanostructured Fe–Co alloys

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 ε_r.     

Nd8.5Dy0.5Fe84.5Co0.5B6合金的晶化工艺

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.     

Synthesis and characterization of Co–Fe nanoparticles supported on mesoporous silicas

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.     

PrBi4Fe0.5Co0.5Ti3O15多铁陶瓷的性能研究

采用传统固相反应法与两步合成法制备了PrBi₄Fe_0.5Co_0.5Ti₃O₁₅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(2M_r)分别为0.315, 0.576 Am²/kg, 比文献报道的Bi₅FeTi₃O₁₅陶瓷的2M_r ( 2.7 Am²/kg ) 高5个数量级, 比掺Co的Bi₅Fe_0.5Co_0.5Ti₃O₁₅陶瓷2M_r ( 7.8×10^-3 Am²/kg ) 高2个数量级。     

Ce2Fe16.5Co0.5合金的磁熵变研究

在氩保护气氛中用熔炼法制备了 Ce2Fe16.5Co0.5合金,通过粉末 X射线衍射和 SQUID 磁强计研究了样品的结构和磁熵变。结果表明 Ce2Fe16.5 Co0.5合金具有菱方Th2Zn17型结构,且存在不同组分的2个相,主相Ce2(Fe,Co)17和次相 Ce(Fe,Co)7。在 242~285K宽温区出现一个磁熵变平台,从而能够满足磁Ericsson型磁致冷机的要求,这对实际磁致冷应用具有现实意义。     

Characterizing the Exchange Interaction of Sm-Co/Co （and Fe65Co35） Magnetic Films

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.     

La3+掺杂Co0.5Ni0.5(Fe0.5Cr0.5)2O4尖晶石红外辐射材料的研究

用固相合成法制备La3+掺杂Co0.5Ni0.5(Fe0.5 Cr0.5)2O4尖晶石体系红外辐射材料,并通过DTA-TG、XRD和IRE-2型红外辐射测试等方法研究了材料的结构特征与红外辐射性能的关系,结果表明:随着La3+含量的增加,La3+以不同的形式进入Co0.5Ni0.5(Fe0.5 Cr0.5)2O4体系中,当La2O3掺杂浓度为5%(质量分数)时,样品的法向全波段辐射率达到0.91.     

Microstructure and magnetic properties of nanostructured Fe–Co powders prepared by series of milling and annealing treatments

Fe_1−xCo_x(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 (H_C) 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 H_C (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 (M_S) due to completion of alloying and grain refinement. Also, compared to series 2, extra annealing treatment for series 3 resulted in larger values of M_S caused by stain relief.     

Structural, Dielectric and Complex Impedance Spectroscopy Studies of Lead Free Ca0.5 ＋xNd0.5-x（Ti0.5 Fe0.5）O3

Structural and various electrical properties of polycrystalline Ca_0.05+xNd_0.5-x(Ti_0.5Fe_0.5)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(σ_ac).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(R_gb) is observed.The R_gb decreases with increasing Ca content.The highε’ observed in present samples are suitable for fabrication of devices.     

X-ray powder diffraction and Mössbauer studies on the formation of Cd0.5Ni0.5Fe2O4/Zn0.5Ni0.5Fe2O4 spinel solid solutions

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 Cd_0.5-αZn_αNi_0.5Fe₂O₄, 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 (Cd_0.5-αZn_αFe_0.5)_tetr[Ni_0.5Fe_1.5]_octO₄ analysis has been undertaken.     

Determination of mechanical properties of consolidated nanocrystalline iron–carbon alloys Fe–0.5%C and Fe–4.5%C by means of echography and acoustic microscopy

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.     

Ba0.5Sr0.5Co0.8Fe0.2O3-δ阴极材料的制备与性能

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.     

阴极材料Ba0.5Sr0.5Co0.8Fe0.2O3-δ的制备和性能

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.     

聚合物协助燃烧法合成La0.8Sr0.2Co0.5Fe0.5O3-δ纳米粉体

为开发新型高性能中温固体氧化物燃料电池阴极材料,以La、Sr、Co和Fe的硝酸盐、葡萄糖和丙烯酰胺为原料,在pH=8-10的碱性条件,通过聚合物协助燃烧法制备了La0.8 Sr0.2 Co0.5 Fe0.5 O3-δ(LSCF)钙钛矿相纳米粉体.用XRD、SEM和TEM表征了LSCF粉体的相结构和微观形貌,结果显示,在...     

Studies on the structural,electrical and magnetic properties of LaCrO3, LaCr0.5Cu0.5O3 and LaCr0.5Fe0.5O3 by sol–gel method

The structural, electrical and magnetic properties of LaCr_0.5M_0.5O₃ (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 LaCr_0.5Cu_0.5O₃ 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 LaCr_0.5Cu_0.5O₃ 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 LaCr_0.5Fe_0.5O₃.     

The impact of cation distribution on the structural and magnetic properties of nonstoichiometric Co0.5Ni0.5+xFe2−xO4 nanoferrites

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...