Growth mechanism of ZnO nanorod/Fe3O4 nanoparticle composites and their photocatalytic properties

ZnO nanorods/Fe₃O₄ nanocomposites as the recyclable photocatalyst were synthesized by a co-precipitation method, with microwave assistant by dropping alkaline solution with Fe₃O₄ nanoparticles into the aqueous of zinc salt. These Fe₃O₄ nanoparticles were the nucleated centers for the ZnO nanorods growth so that these nanorods ended with aggregated Fe₃O₄ nanoparticles. The growth processes and mechanism are explained as those insoluble zinc hydroxides prefer to nucleate on the surface of Fe₃O₄ nanoparticles (heterogeneous nucleation) rather than nucleated as isolated ZnO nanostructures (homogeneous nucleation). These nanocomposites have strong photocatalytic ability to reduce RhB and moderate magnetization, which make them being good recyclable photocatalysts.     

Ultralow detection limit of giant magnetoresistance biosensor using Fe_3O_4–graphene composite nanoparticle label

A special Fe_3O_4nanoparticles–graphene(Fe_3O_4–GN) composite as a magnetic label was employed for biodetection using giant magnetoresistance(GMR) sensors with a Wheatstone bridge. The Fe_3O_4–GN composite exhibits a strong ferromagnetic behavior with the saturation magnetization M_S of approximately 48 emu/g, coercivity H_C of 200 Oe, and remanence M_r of 8.3 emu/g, leading to a large magnetic fringing field. However, the Fe_3O_4 nanoparticles do not aggregate together, which can be attributed to the pinning and separating effects of graphene sheet to the magnetic particles. The Fe_3O_4–GN composite is especially suitable for biodetection as a promising magnetic label since it combines two advantages of large fringing field and no aggregation. As a result, the concentration x dependence of voltage difference |?V| between detecting and reference sensors undergoes the relationship of |?V| = 240.5 lgx + 515.2 with an ultralow detection limit of 10 ng/mL(very close to the calculated limit of 7 ng/mL) and a wide detection range of 4 orders.     

Charge and orbital order in Fe3O4

Charge and orbital ordering in the low-temperature monoclinic structure of magnetite (Fe3O4) is investigated using the local spin density approximation with Coulomb interaction correction method. While the difference between t(2g) minority occupancies of Fe(2+)(B) and Fe(3+)(B) cations is large and gives direct evidence for charge ordering, the screening is so effective that the total 3d charge disproportion is rather small. The charge order has a pronounced [001] modulation, which is incompatible with the Anderson criterion. The orbital order agrees with the Kugel-Khomskii theory.     

原位氧化水解法制备网状结构Fe3O4薄膜

在壳聚糖膜上通过原位氧化水解反应制备了网状结构的Fe3O4薄膜.采用X射线衍射、扫描电子显微镜和热重差热分析对产物进行了分析和表征,结果表明,所制备的Fe3O4膜为纯相反尖晶石结构;网孔直径大约50～300nm,网壁厚度大约30nm;Fe3O4转化为γFe2O3的温度约为458℃.     

The magnetic hyperfine interaction of111Cd in the spinels Fe3O4 and Co3O4

The perturbed angular correlation (PAC) method was applied to study the temperature dependence of the magnetic hyperfine fields in¹¹¹In-doped polycrystalline Fe₃O₄ and Co₃O₄. The critical behaviour near the magnetic phase transitions has been investigated. The changes occuring near the Vervey transition in Fe₃O₄ and the path of the supertransferred magnetic fied in Co₃O₄ are discussed. The results are compared with results obtained from Mössbauer spectroscopy.     

Dissociation reactions of CO Gas on Fe and Fe3O4 surfaces observed by Raman-ellipsometry spectroscopy

A combined system of Raman spectroscopy and ellipsometry is developed for the study of catalyst surfaces on which a chemical reaction is taking place. The dielectric function and the thickness of a surface layer or a surface compound produced in the reaction are analyzed by ellipsometry; vibrational modes of the compound and surface species are analyzed by Raman spectroscopy, and the products in the gas phase by mass spectrometry. The system is applied to the study of the Boudouard and dissociation reactions of CO molecules on Fe and Fe₃O₄ catalysts. A surface layer produced by diffused C and O atoms, a thin oxide layer produced on the Fe by the CO dissociation reaction, and graphite layers produced by the Boudouard reaction are analyzed. Raman spectra reveal the existence of several kinds of carbon species such as defective graphite and an Fe carbide formed on the Fe and Fe₃O₄ surfaces. Specific Raman bands at 1121 and 1147 cm^-1 are tentatively concluded to be produced from microscopic clusters of surface graphite. The reaction of the defective graphite with H₂ gas is found to be stepwise on a time scale of seconds.     

Spin and orbital magnetic moments of Fe3O4

We present measurements of the spin and orbital magnetic moments of Fe3O4 by using SQUID and magnetic circular dichroism in soft x-ray absorption. The measurements show that Fe3O4 has a noninteger spin moment, in contrast to its predicted half-metallic feature. Fe3O4 also exhibits a large unquenched orbital moment. Calculations using the local density approximation including the Hubbard U method and the configuration interaction cluster-model suggest that strong correlations and spin-orbit interaction of the 3d electrons result in the noninteger spin and large orbital moments of Fe3O4.     

Chemical reactions induced by 40 keV He+ ions in Fe3O4 and α-Fe2O3

The chemical reactions induced by 40 keV He⁺ ions in α-Fe₂O₃ and Fe₃O₄ were investigated by the conversion electron Mössbauer spectroscopy(CEMS). Magnetite(Fe₃O₄) was formed upon the bombardment of α-Fe₂O₃, whereas no change was observed in Fe₃O₄. The initial G value for Fe₃O₄ formation is estimated to be 3.5×10^?4 for 100 nm depth from the surface. The application of CEMS and sputtering technique to ion bombardment chemistry is discussed.     

Fe3O4薄膜的电输运及光诱导特性研究

用脉冲激光沉积法在(111)Si衬底上成功制备了高度择优取向的Fe₃O₄薄膜.电阻-温度关系表明Fe₃O₄薄膜的Verwey转变(T_V)约在122 K,低温段(T_V)输运特征满足Mott变程跳跃模型,高温段(T>T_V)为小极化子输运.激光作用下的光电导实验发现,在整个温区表现为光致电阻率减小,而且低温段的电阻变化率比高温段要大很多.分析认为Fe₃O₄薄膜的光致电阻率变化主要与激光激发t_2g电子的转移有关. 关键词： 3O₄薄膜')" href="#">Fe₃O₄薄膜 小极化子 光诱导特性     

Monte Carlo simulation of dose distribution in water around 57Fe3O4 magnetite nanoparticle in the nuclear gamma resonance condition

In this work was proposed a new radiotherapy enhancement method consisting of the administration of magnetic nanoparticles into the cells with further irradiation with a gamma-ray beam. As a result, adjusting the energy distribution of a gamma-ray beam and ⁵⁷Fe abundance it is possible to achieve an extremely intensive electron emission because of a nuclear resonance. The produced conversion and Auger electrons can be used as an effective tool for DNA lesions production. We developed a Monte Carlo model for an electron and gamma emission by ⁵⁷Fe nucleus using the Geant4 program package. The parameters of a resonant absorption were taken from Mössbauer spectra of magnetite nanoparticles synthesized for the administration into live cells. The space distribution of the radiation dose showed an increase in the dose of 2–2.5 times in the case of the natural abundance and more than 50 times in the case of the 66 % enrichment of the nanoparticles.     

Growth and characterization of Fe3O4 nanoparticles in silica matrix

Nano-magnetic Fe₃O₄ particles coated with silica are synthesized. The study of structural and magnetic properties was carried out using X-ray diffraction, scanning electron microscopy, transmission electron microscopy, and vibrating sample magnetometer (VSM) techniques. The VSM results show that these kinds of composite particles exhibit superparamagnetic behavior with zero coercivity and remanence. The magnetic spheroid alumina carriers containing these magnetic composite particles were prepared by an internal gelation process. The SiO₂ coatings prevent the reaction between Fe₃O₄ and Al₂O₃ during the sintering process and maintain the superparamagnetic behavior of the catalyst carriers.     

Insulator-metal transition in thin films of ferrite Fe3O4

Insulator-metal transition in Fe₃O₄ is analysed on the basis of electron-electron correlation of nearest neighbour sites. A double time Zubarev Green function technique is used. It is shown that up to 120 °K system stays in a localised state and then goes into the band-state. The band-state completely disorders itself at 300 °K. Conductivity and thin film data are briefly analysed.     

Determination of the recoilless-fraction for57Fe in Fe3O4 by the Mössbauer Faraday effect

We have observed the Mössbauer Faraday effect in nonstoichiometric Fe₃O₄ by using a Mössbauer polarimeter. Experimental results demonstrated that electronic hopping above the Verwey temperature between Fe²⁺?Fe³⁺ ions on the octahedral sites is a localized phenomenon only and the recoilless fractions of⁵⁷Fe nuclei in Fe_3?vO₄ (v=0.02) are 0.71 for A sites and 0.62 for B sites, respectively.     

The structure-tunable synthesis and magnetic properties of Fe3O4 nanocrystals

Magnetite nanocrystals with tunable crystalline structures (orthorhombic and cubic) were synthesized via a simple oxidation-coprecipitation approach basing on the reaction of FeSO₄·7H₂O with C₆H₁₂N₄. The average diameter of prepared orthorhombic Fe₃O₄ nanorods were 15 nm while their lengths were approximately 150~200 nm. As-prepared cubic counterparts were composed of 10 nm sized nanoparticles. XRD, FESEM, TEM, SAED and HRTEM were then used to characterize our samples. In addition, magnetic measurements showed the saturation magnetization of orthorhombic magnetite was lower than that of cubic ones. Mössbauer spectroscopy verified the samples possessed the nature of cubic magnetite. Finally, a possible growth mechanism for orthorhombic nanorods and cubic nanoparticles was also discussed.     

Fe3O4@Au纳米材料的制备和光谱性质

采用共沉淀法制备了Fe3O4纳米颗粒,并以其为晶种利用晶种生长法制备了Fe3O4@Au磁性复合纳米粒子。吸收光谱显示Au壳层成功包覆在了Fe3O4纳米核的表面。以结晶紫为探针分子的表面增强拉曼散射（SERS）光谱展示了Fe3O4@Au良好的SERS活性。     

磁场下合成Fe3O4粉体的隧道磁阻

通过在半金属Fe3O4合成过程中外加磁场的方法,改变样品粒子的表面结晶状态和晶格缺陷,研究了由此引起的Fe3O4输运性质的变化.合成的Fe3O4粉体的主要导电机理均为自旋极化隧穿和高阶跃迁电导,电阻随温度升高成指数降低,电阻与电压显示了非线形相关性,磁阻与磁场的关系为蝴蝶形,是典型的隧道磁阻特征.与没有外加磁场时合成的样品比较,外加磁场合成的样品显示了更低的电阻和更高的磁阻.由于Fe3O4具有高的居里温度,引起Fe3O4粉体的磁阻随温度升高而降低缓慢.     

Micromagnetic model of the Richter-type relaxation in vacancy-doped Fe3O4

Isothermal disaccommodation curves in vacancy-doped magnetite at room temperature show a typical Richter-type behaviour. Magnetic susceptibility decreases asymptotically according to a relaxation time of about 10² s, which is analyzed in terms of a progressive stabilization of the domains walls. The relaxation strength, vacancies and the restoring pressure on the Bloch walls are closely related.     

新型螯合磁性纳米Fe_3O_4的制备及其性能研究

采用共沉淀法制备了磁性四氧化三铁(Fe3O4)纳米粒子,并通过硅烷偶联剂对其表面进行改性,进一步在其表面偶联修饰氨基硫脲,制备了螯合磁性纳米Fe3O4粒子。利用广角X射线衍射仪(WAXD)、红外光谱仪(FTIR)、分光光度计等对磁性纳米粒子的结构和性能进行了表征。结果表明,纳米Fe3O4为反尖晶石结构,通过偶联修饰可以实现氨基硫脲在纳米粒子表面的化学改性。螯合磁性纳米粒子具有良好的分散性和磁响应性,且对多种金属离子(Pb2+、Hg2+、Zn2+、Cd2+)具有良好的螯合效果。     

有机盐制备的Fe3O4-葡聚糖纳米粒子的磁性能及表征

利用葡糖酸铁(C12H22FeO14·2H2O)和柠檬酸铁(C6H5O7Fe·5H2O)参与的化学共沉积法制备出单分散核心氧化铁的平均粒径为4.1nm,葡聚糖厚度约为11nm,总体平均粒径为26nm的Fe3O4葡聚糖复合纳米粒子.研究结果表明,复合粒子Fe3O4葡聚糖具有超顺磁性.制备过程中没有N2保护,得到的Fe3O4无机粒子的晶体结构几乎没有发生变化,证明了有机盐的抗氧化性,合成的Fe3O4葡聚糖复合纳米粒子具有较好的磁性能.其在室温下(300K)的饱和磁化强度为52emu/g,低温下(5K)的饱和磁化强度为63emu/g.并利用TEM、XRD、DLS和VSM(振动样品磁强计)等手段对其粒结构、形态、粒径和磁性能进行了表征.