Structural Analysis of Eu2Mn2／3Ta4／3O7 with a Pyrochlore-Related Structure

Eu2Mn2/3Ta4/3O7 specimen was synthesized from Eu2O3, MnO and Ta2O5 in a reducing atmosphere. Structure analysis was carried out by Rietveld method from X-ray diffraction data. The X-ray diffraction profile calculated with monoelinic C2/c model was in a good agreement with the observed X-ray diffraction patterns since several small peaks of super lattice could be also assigned with C2/c symmetry in addition to fundamental reflection peaks. Eu2Mn2/3Ta4/3O7 has two kinds of distorted (Mn, Ta)O6 octahedra and HTB layers, which deviates from the regular forms. Europium atoms coordinate to eight or seven oxygen atoms and lead to two kinds of polyhedra, EuO8 and EuO7 in this compound.     

Anisotropic Magnetoresistance of Perovskite La2／3Ca1／3 MnO3 ／YBa2Cu4O8／La2／3Cal／3MnO3 Trilayer Films

The anisotropic magnetoresistance (MR) of La2/3Ca1/3MnO3(LCMO)/YBa2Cu4O8 (YBCO) /LCMO sandwiches on (001) SrTiO3 were investigated. Single layer LCMO and sandwiches show in-plane anisotropy of MR. MR strongly depends on the magnetic field direction. A nearly sinusoidal dependence on the angle between the applied magnetic field and the film plane or transport current was observed. A positive MR was present with lower fields applied not only out-of-plane but also in-plane.     

Synthesis, Electrical and Magnetic Properties of Fe304 Doped by Dy^3＋

The Dy^3＋ -doped Fe3O4 samples were synthesized by sol-gel method, and the effects of dopant on the electrical and magnetic properties were investigated. According to XRD analysis, the high concentration doping of dysprosium ions in Fe3O4 can not be obtained due to the difference of ionic radius, and Fe^3 ＋ ions are replaced by only a small amount of dysprosium ions. The magnetic property was characterized by VSM. The substitution results in the change of saturation magnetization, which may be due to the complex effects of increasing magnetization resulted from Dy^3＋ substitution and decreasing magnetization resulted from the impurity. The electrical property was characterized by four-probe method. With the increasing eoped content, magnetoresistance also increases, then decreases, and increases again. The spin-polarization of doped samples is lower than that of Fe3O4. Lower spin-polarization results in lower tunneling magnetoresistance. Fortunately, barrier was obtained by the second phase at the same time when sample was synthesized. The increase of appropriate barrier height leads to the change of tunneling magnetoresistance.     

Combustion Synthesized Porous Body of Fe3O4/Al System by Controlled Microwave Heating and Heating Behavior of the Products

Microwave-induced substitutional combustion reaction was utilized to fabricate porous ceramic composite from Fe₃O₄/Al powder mixtures.The porous composite body was obtained by controlling the combustion reaction progress in a 2.45 GHz single mode applicator.Prior to the fabrication of the porous body,heating behavior of the powder mixtures were studied in the separated electric（E）and magnetic（H）fields.In addition,heating ability of the microwave fabricated porous product was also investigated.Fe₃O₄powder can be heated up easily in both maximum H and E field,but a better heating was observed in the maximum H field.Regardless of the mixtures ratio（mixing compositions）,maximum H field shows better heating characteristics.In E-field heating,temperature of the Fe₃O₄ samples decreased sharply when Al powder was added.However,the same phenomenon was not observed in the maximum H field heating.Thus,fabrication of the porous composite body was carrying out in maximum H field.Through an adequate control of the reaction progress,products with a porous structure consisting of well-distributed metal particles in the alumina and/or hercynite matrix were obtained.Consequently,heating of the fabricated porous composite body was also been successfully carried out in the maximum H field.Product phases and microstructure were the main factors influencing the heating ability of the porous composite body.     

Effect of Yb2O3 additives on structure and transport properties of YBa2Cu3O7-δ

The effects of Yb2O3 particles on the microstructure and transport properties of YBa2Cu3O7-δ(YBCO) were investigated through resistance-temperature(R-T),scanning electron microscope(SEM),X-ray diffraction(XRD) and the critical current density(Jc) versus applied magnetic field(Jc-B) measurements.YBCO powder with Yb2O3 additives was synthesized using standard solid state reaction technique.Rietveld refinements of X-ray diffraction showed that both Yb2O3 and YBCO phases coexisted in the products.The critical current density(Jc) exhibited a maximum at x=0.05 in YBCO+xYb2O3 systems.Moreover,small additions of Yb2O3 in YBCO could enhance Jc by applying the magnetic field,although the superconducting temperature(Tc) decreased monotonically with increasing additive content.The characteristic behavior of Jc might come from the counterbalance of two effects simultaneously,which was caused by the inhomogeneity of grains distribution in nano-scale and degradation on superconducting properties.     

Hydrogen Embrittlement Processes and AL／AL2O3 Hydrogen Resistance Coatings of NdFeB Magnets

After analyzing the phenomena and processes of hydrogen embrittlement of NdFeB permanent magnets, RF magnetron sputtering was used to fabricate A1 thin films and then oxidized to form the Al/Al2O3 composite films on the magnets as the hydrogen resistance coatings. SEM and EDS were used to examine the morphology and composition respectively. Hy-drogen resistance performance was tested by exposing the magnets in 10 MPa hydrogen gas at room temperature. The results show that the magnets with 8μm Al/Al2O3 coatings can withstand hydrogen of 10 MPa for 65 min without being embrittledinto powd er. The samples with and without hydrogen resistance coatings have almost the same magnetic properties.     

A Novel Structure of ZnS：Tm^3＋ TFEL Device

A novel ZnS :TmF3 TFEL device with the structure of ITO/SiO2/ZnS : TmF3/SiO2/ZnS : TmF3/SiO2/Al was prepared by e-beam evaporation method. The EL emission spectra show that the brightness of the novel structure devices greatly increases compared with that of devices with traditional double insulator structure, and the ratio of blue emission to red emission of the novel structure device is also improved. The improvement of the EL characteristics of this kind TFEL device is attributed to both of the electron acceleration and the ZnS/SiO2 interface.     

Long-lasting phosphorescence study on Y_3Al_5O_（12） doped with different concentrations of Ce~（3＋）

Long-lasting phosphorescence (LLP) was observed in Ce-doped Y3Al5O12 phosphors synthesized in reducing atmosphere. The characteristic emission of the 2D-2F5/2 and 2D-2F7/2 transition of Ce3+ in photoluminescence (PL) and LLP spectra was studied. It was interesting that the ratio between the peak areas of 2D-2F5/2 and 2D-2F 7/2 transitions in the PL spectrum was different from the ratio of that in LLP emission spectrum. And the ratios had different change regularities with increased Ce3+ concentration. The p...     

Physico-chemical properties of 3-methoxy-2-nitrobenzoates of some rare earth elements（Ⅲ）

The complexes of 3-methoxy-2-nitrobenzoates of Pr(III), Nd(III), Sm(III), Eu(III), Gd(III), Tb(III), Er(III) and Tm(III) with the formula: Ln(C8H6NO5)3·2H2O, where Ln=lanthanides(III), were synthesized and characterized by elemental analysis, Forier transform irtrared (FTIR) spectroscopy, magnetic and thermogravimetric studies and also by X-ray diffraction (XRD) measurements. The complexes had col- ours typical for Ln(III) ions. The carboxylate groups bound as bidentate chelating. On heating to 1173 K in air they decomposed in the same way, at first, dehydrated in one step to anhydrous salts, and then decomposed to the oxides of respective metals with intermediate formation of the oxycarbonates. The enthalpy values of the dehydration process changed from 133.72 to 44.50 kJ/mol. Their solubility in water at 293 K was of the order of 10-4 mol/dm3. The magnetic moments of analysed complexes were determined by Gouy’s method in the range of 76-303 K.     

Study on Modification of Sm2O3 by Ni／Sepiolite Catalyst

A series of Ni-Sm/sepiolite catalysts were prepared by impregnation. The modification of Sm2O3 for Ni/sepiolite was investigated by TPR, XPS and poisoning of CS2, respectively. The results indicate that the addition of Sm2O3 improves the activity of hydrogenation and anti-poisoning ability of Ni/sepiolite catalyst, and it also increases the dispersion of nickel atoms over support and the amount of active nickel atoms in catalyst. Effect of Sm203 on Ni/sepiolite catalyst ineludes not only electronic effect but also steric effect, whereas electronic effect seems to be principal.     

Anisotropic Magnetoresistance of Perovskite La_(2/3)Ca_(1/3)MnO_3/YBa_2Cu_4O_8/La_(2/3)Ca_(1/3)MnO_3 Trilayer Films

Magneticanisotropyhasbeenfoundinmanyex oticmaterials,suchasmetallicsuperlatticeswithgi antmagnetoresistanceeffectsandthehightempera turesuperconductingoxideYBa2Cu3O7 δ[1～4].The anisotropycouldfindnovelusesinnewdeviceappli cations.Agoodexampleisthehig…     

高能球磨对La_(2/3)Ca_(1/3)MnO_3晶体结构和磁性的影响

通过在传统的烧结工艺上加上球磨工艺制备了单相 L a2 / 3Ca1 / 3Mn O3氧化物 ,研究了球磨对氧化物的结构和磁性能的影响 ,发现晶格常数和晶胞体积增大 ,但晶体结构类型基本不变 ,仍为钙钛矿四方相结构 ,而交流磁化率、磁化强度、居里温度减小。球磨引起氧的欠缺、无序效应 ,对电阻有一定的影响     

Magnetic properties and magnetocaloric effects of manganite (La0.8Ho0.2)2/3Ca1/3MnO3 and (La0.5Ho0.5)2/3Ca1/3MnO3

We reported the magnetic properties and magnetocaloric effects (MCE) of (La_0.8Ho_0.2)_2/3Ca_1/3MnO₃ and (La_0.5Ho_0.5)_2/3Ca_1/3MnO₃ nanoparticles by sol-gel technique. With this method, we were able to obtain the samples with particle diameters ranging from 50 to 200 nm. In the (La_1-xHo_x)_2/3Ca_1/3MnO₃ compound, an external magnetic field induced a magnetic transition from an paramagnetic phase to a ferromagnetic phase above T_s=105-135 K, leading to magnetocaloric effects. The maximum value of ΔS_M was 1.19 J/(kg·K) at 100 K and 2.03 J/(kg·K) at 152 K for a magnetic field change of 5 T. Because both samples had large relative cooling power (RCP) and wide δT_FWHM, the study on systems with the (La_1-xHo_x)_2/3Ca_1/3MnO₃-related magnetic transitions may open an important field in searching good magnetic materials.     

La2/3(Ca60Ba40)1/3MnO3的磁电阻与磁化强度及其相关性

用固相反应法制备了La2/3(Ca60Ba40)1/3MnO3多晶材料,测量了77K～320K范围内的磁化曲线及在77K～350K范围内0～1.0T外磁场下的电阻率。结果表明低场磁电阻与高场磁电阻随外磁场的变化与磁化强度(M2)的变化存在着一定相关性,采用ρ(M)∝1-M2及低温隧穿磁电阻效应和逾渗模型解释了实验结果。     

Magnetic properties and magnetocaloric effects of manganite (La_0.8Ho_0.2)_2/3Ca_1/3MnO₃ and (La_0.5Ho_0.5)_2/3Ca_1/3MnO₃

We reported the magnetic properties and magnetocaloric effects(MCE) of(La0.8Ho0.2)2/3Ca1/3MnO3 and(La0.5Ho0.5)2/3Ca1/3MnO3 nanoparticles by sol-gel technique.With this method,we were able to obtain the samples with particle diameters ranging from 50 to 200 nm.In the(La1-xHox)2/3Ca1/3MnO3 compound,an external magnetic field induced a magnetic transition from an paramagnetic phase to a ferromagnetic phase above Ts=105-135 K,leading to magnetocaloric effects.The maximum value of ΔSM was 1.19 J/(kg·K) at 100 K and 2.03 J/(kg·K) at 152 K for a magnetic field change of 5 T.Because both samples had large relative cooling power(RCP) and wide δTFWHM,the study on systems with the(La1-xHox)2/3Ca1/3MnO3-related magnetic transitions may open an important field in searching good magnetic materials.     

Nd2Fe14B/Fe3B基纳米复合粘结磁体的磁特性

通过实验研究了Nd2Fe14B／Fe3B双相纳米复合磁粉分别与几种不同性能的磁粉复合成粘结磁体后磁性能的变化。通过对复合磁体的理论分析得知，由Nd2Fe14B／Fe3B与RE2Fe14B或铁氧体磁粉复合成的粘结磁体中，成分间并未发生化学反应。以Nd2Fe14B／Fe3B铁氧体复合粘结磁体为例，根据理论分析推出的剩磁Br-成分含量关系曲线与实际曲线吻合得很好，表明剩磁与成分含量间存在着近似的线性关系，从而可通过数学手段建立磁性能参数与成分含量的函数关系式，用于简化混粉工艺。另外，添加铁氧体可对该复合磁体较差的热稳定性起到补偿作用，并减少了磁不可逆损失。     

Effects of cobalt addition on microstructure and magnetic properties of PrNdFeB/Fe_7Co_3 nanocomposite

The permanent magnetic nanocomposite PrNdFeB/Fe_7Co_3 ribbons were prepared by directly quenching, and the microstructure and magnetic influence of composite materials with Co substitution were studied. The phase identification and the magnetic properties were measured by X-ray diffraction(XRD) and vibrating sample magnetometry(VSM). Microstructure observation was performed using scanning electron microscopy(SEM). The crystallization temperatures of the hard magnetic phase and the soft magnetic phase were measured using differential scanning calorimetry(DSC). The experimental results showed that Co addition improved the Curie temperature of magnets. When the ribbons were melt-spun at 35 m/s, the added content of Co was 4 at.%, and the magnetic properties were the best, which were remanence(Br) of 0.379 T, coercivity(Hci) of 344.4 kA/m, the maximum magnetic energy product(BH)max of 32.6 kJ/m~3. Besides, the activation energy of each phase was calculated by Kissinger equation, which was 310.4 kJ/mol of Fe_7Co_3 phase and 510.2 kJ/mol of 2:14:1 phase, respectively.     

Photocatalytic activity of cerium-doped mesoporous TiO2 coated Fe3O4 magnetic composite under UV and visible light

A novel kind of magnetically separable photocatalyst of cerrium-doped mesoporous titanium dioxide coated magnetite (Ce/MTiO2/ Fe3O4) was prepared and its activities under UV and visible light were reported. The catalysts with Ce/MTiO2 shell and Fe3O4 core were pre-pared by coating photoactive Ce/MTiO2 onto a magnetic Fe3O4 core through the hydrolysis of tetrabutyltitanate (Ti(OBu)4, TBT) with pre-cursors of ammonium ceric nitrate and TBT in the presence of Fe3O4 particles. The MTiO2 shell was for photocatalysis, the Fe3O4 core was for separation by the magnetic field and the doped Ce was used to enhance the photocatalytic activity of MTiO2. The morphological, struc-tural and optical properties of the prepared samples were characterized by Brunauer-Emmett-Teller (BET) surface area, transmission electron microscopy (TEM), X-ray diffraction (XRD) and UV-vis absorption spectroscopy. The effect of cerrium-doped content on the photocatalytic activity was studied and the result revealed that 0.5 mol.% Ce/MTiO2/Fe3O4 exhibited highest photoactivity. The photocatalytic activities of obtained photocatalysts under UV and visible light were estimated by measuring the degradation rate of methylene blue (MB, 50 mg/L) in an aqueous solution. The results showed that the prepared photocatalyst was activated by visible light and used as effective catalyst in photooxi-dation reactions. In addition, the possibility of cyclic usage of the prepared photocatalyst was also confirmed. Moreover, Ce/MTiO2 was tightly bound to Fe3O4 and could be easily recovered from the medium by an external magnetic filed. So, the photocatalyst can be reused without any mass loss. It can therefore be potentially applied for the treatment of water contaminated by organic pollutants.     

纳米Fe3O4应用及制备工艺研究进展

纳米Fe₃O₄是一种具有优异特性的磁性纳米材料。本文介绍了纳米Fe₃O₄的基本性质及应用, 综述了沉淀法、水热法、微乳液法、溶胶-凝胶法等纳米Fe₃O₄制备工艺的原理、研究现状、优缺点及发展趋势, 并指出将多种工艺相结合可制备出更优异的纳米Fe₃O₄。     

稀土磁性复合微球的制备及表征

以聚乙二醇磁性胶体粒子为种子 ,运用分散聚合法 ,同时掺入稀土离子 ,制备出表面配位有稀土离子的磁性聚苯乙烯微球 ,该微球粒径为 6 0～ 180 nm,考察了稀土磁性微球的形态和结构。并用电镜、原子吸收光谱、红外光谱对其性质进行了表征。