Starch vermicelli template for synthesis of magnetic iron oxide nanoclusters

A novel method for fabricating magnetic iron oxide nanoparticles was achieved by using transparent vermicelli template as a new stabilizing material. The morphology of the as-prepared magnetic iron oxide deposited on the surface of vermicelli was observed as nanoclusters. The magnetization of the magnetic iron oxide nanoparticles at room temperature was decreased after carbonization at 200 °C. Therefore the thermal decomposition of iron oxide nanoparticles stabilized by starch vermicelli template yielded iron oxide/carbon nanocomposites with the soft magnetic behavior which are useful for biomedical applications.     

Interplay of iron and rare-earth magnetic order in rare-earth iron pnictide superconductors under magnetic field

The magnetic properties of iron pnictide superconductors with magnetic rare-earth ions under strong magnetic field are investigated based on the cluster self-consistent field method. Starting from an effective Heisenberg model, we present the evolution of magnetic structures on magnetic field in RFeAsO(R = Ce, Pr, Nd, Sm, Gd, and Tb) and RFe_2As_2(R =Eu) compounds. It is found that spin-flop transition occurs in both rare-earth and iron layers under magnetic field, in good agreement with the experimental results. The interplay between rare-earth and iron spins plays a key role in the magneticfield-driven magnetic phase transition, which suggests that the rare-earth layers can modulate the magnetic behaviors of iron layers. In addition, the factors that affect the critical magnetic field for spin-flop transition are also discussed.     

Invar effect in iron based fcc alloys

A model of interacting virtual bound states is used to calculate the atomic magnetic moments in iron based fcc alloys. This clearly shows that the magnetic moment not only depends on environment but on magnetic order too. Consequently there is a change in magnetic moment between 0 K and the ordering temperature which leads to a change in cohesive energy. If the iron–iron exchange coupling constant is negative the Invar effect arises from iron atoms surrounded by iron atoms whose magnetic moments are parallel to this of the central atom.     

Magnetoelectric and magnetoelastic interactions in NdFe3(BO3)4 multiferroics

Complex experimental and theoretical investigations of the magnetic, magnetoelectric, and magnetoelastic properties of neodymium iron borate NdFe₃(BO₃)₄ along various crystallographic directions have been carried out in strong pulsed magnetic fields up to 230 kOe in a temperature range of 4.2–50 K. It has been found that neodymium iron borate, as well as gadolinium iron borate, is a multiferroic. It has a much larger (above 300 μC/m²) electric polarization controlled by the magnetic field and giant quadratic magnetoelectric effect. The exchange field between the rare-earth and iron subsystems (～50 kOe) has been determined for the first time from experimental data. The theoretical analysis based on the magnetic symmetry and quantum properties of the Nd ion in the crystal provides an explanation of the unusual behavior of the magnetoelectric and magnetoelastic properties of neodymium iron borate in strong magnetic fields and correlation observed between them.     

The effect of aluminum overlayers on the magnetization of iron and iron-nickel alloys

Iron and iron-nickel films 2 to 10 nm thick were prepared in a high vacuum magnetometer. The magnetic moment of each iron or iron nickel film was measured in situ, then an aluminum overlayer (2–30 nm thick) was deposited on the ferromagnetic film, and the magnetic moment was again measured in situ. The aluminum overlayer decreases the magnetic moment as if the iron film or iron-nickel film thickness decreases by about 0.3 to 0.5 nm.     

Effect of a pulsed magnetic field on the diffusion of aluminum in iron and the fine-structure parameters of iron

The effect of a pulsed magnetic field with a strength in the range 0–557.2 kA m^?1 and a frequency in the range 0–8 Hz at a temperature of 730°C on the diffusion of aluminum in iron, the microhardness of iron, and the dislocation density in iron has been experimentally investigated by metallography and X-ray diffraction. It is established that a pulsed magnetic field significantly affects the diffusion coefficient of aluminum and the dislocation density in iron. Possible mechanisms of the influence of a pulsed magnetic field on the characteristics measured are discussed.     

Stabilizing oxide layers on iron particles

Pyrophoric iron powders at different stages of stabilization by oxygen (0–8% by weight) were annealed at 255 or 500°C up to 571 h. During this procedure the magnetic moments first decreased by some per cent and then increased above the initial values. The shape of the magnetic moment versus oxygen uptake curves remained unchanged. The increase of the magnetic moments as a function of time is correlated with a decrease of the specific surface area of the powders. The Mössbauer spectrum of partially stabilized powders is different from that observed on completely stabilized powders and shows a hitherto unknown magnetic iron oxide while X-ray investigations suggest this oxide to be a special iron deficient Fe₃O₄ (spinel) containing vacancies on the octahedral sites distributed at random. The spins in the oxide should then be coupled in an antiparallel way to the underlying iron core in order to explain the measured magnetic moments.     

Magnetic Ordering Dependence on Iron Ions Distribution in Cu<Subscript>2</Subscript>FeBO<Subscript>5</Subscript> Ludwigite

A comparative analysis of the copper and iron ions bonds exchange energies was conducted for various variants of orderings and distributions of iron ions among crystallographic positions in ludwigite Cu₂FeBO₅. Analysis showed that the exchange bonds of iron ions play a key role in the formation of magnetic order. The magnetic ordering strongly depends on the distribution of iron ions among the positions. In the case when the Fe³⁺ is in the same position as in Fe₃BO₅, the most favorable magnetic structure is similar to the magnetic structure of ludwigite Fe₃BO₅. In other cases, the type of magnetic ordering is different.     

Biological tissue magnetism in the frame of iron overload diseases

The conspicuous magnetic properties of iron, paradoxically, rarely participate in the methods routinely employed in the clinical environment to detect iron containing species in tissues. In the organism iron is just a trace metal and it mostly occurs as part of haemoproteins or ferritin, which show paramagnetic, diamagnetic or antiferromagnetic behaviour, hence resulting in a very low contribution to the tissue susceptibility. Detailed magnetic measurements make it nowadays possible to identify such species in tissues that correspond to individuals with iron overload pathologies. Since, as alternatives to the conventional biopsy, magnetism-based noninvasive techniques to diagnose and manage such diseases are recently under development, the deep knowledge of the magnetic properties of the different forms of iron in tissues is of high applied interest.     

Effect of the number of iron oxide nanoparticle layers on the magnetic properties of nanocomposite LbL assemblies

Aqueous colloidal suspension of iron oxide nanoparticles has been synthesized. Z-potential of iron oxide nanoparticles stabilized by citric acid was −35±3 mV. Iron oxide nanoparticles have been characterized by the light scattering method and transmission electron microscopy. The polyelectrolyte/iron oxide nanoparticle thin films with different numbers of iron oxide nanoparticle layers have been prepared on the surface of silicon substrates via the layer-by-layer assembly technique. The physical properties and chemical composition of nanocomposite thin films have been studied by atomic force microscopy, magnetic force microscopy, magnetization measurements, Raman spectroscopy. Using the analysis of experimental data it was established, that the magnetic properties of nanocomposite films depended on the number of iron oxide nanoparticle layers, the size of iron oxide nanoparticle aggregates, the distance between aggregates, and the chemical composition of iron oxide nanoparticles embedded into the nanocomposite films. The magnetic permeability of nanocomposite coatings has been calculated. The magnetic permeability values depend on the number of iron oxide nanoparticle layers in nanocomposite film.     

Growth and magnetic properties of the sandwich structure Fe/magnetic silicide/Si(100) obtained from in situ optic and magneto-optic data

It is demonstrated by the Surface Magneto-Optic Kerr Effect and Differential Reflectance Spectroscopy methods that structures free of magnetically dead layers can be created by the deposition of iron at room temperature onto a prefabricated magnetic silicide layer. The magnetic silicide can be formed by the deposition of iron at 70 ^°C onto a layer of amorphous silicon prefabricated on Si(100). Both in the silicide and the iron film, magnetism onsets after the iron amount deposited reaches some critical value. The spontaneous magnetization vector in the iron film changes its direction twice during the film growth. Sufficiently thick iron films persist being ferromagnetic in air for years.     

Structure and magnetic properties of the oxide layers on iron ultrafine particles

5 . The γ-Fe particles, because of their paramagnetic nature, are very convenient for investigation on the attributes of iron oxide layers formed on the particle surfaces. Structures, morphologies and magnetic properties of the oxide layers covering the iron ultrafine particles have been studied using transmission electron microscopy observation, magnetic property measurement, X-ray diffraction and annealing treatment. Convincing evidences established that the iron oxide layers are not continuous and consist of very fine crystallites, and that these layers are non-ferromagnetic and have no contribution to the saturation magnetization of the iron particles. The iron oxide layers formed at room temperature was determined to be Fe₃O₄. Additionally, a brief annealing of the iron particles in air were performed to examine magnetic properties of the formed iron oxide layers and ultrafine oxide particles. Received: 30 April 1996/Accepted: 5 November 1996     

Onset of magnetization in monolayer films

Correlations between structural and magnetic properties for ultra-thin iron films are discussed. Some selected methods of structural and magnetic analysis are reviewed. The onset of magnetism for submonolayer Fe(110) film on W(110) is explained based on STM (scanning tunneling microscopy) imaging. Hyperfine magnetic fields in iron films sandwiched between Cr show unusual temperature behavior due to the influence of magnetic ordering in Cr. Magnetic properties of metastable iron phases on Cu and Ru are discussed, based on CEMS measurements.     

Mössbauer effect in iron and dilute iron based alloys

Fifteen years of Mössbauer Effect (ME) studies have significantly widened the insight into the physical properties of iron and iron based alloys. In this review article the various contributions to the hyperfine interactions as measured with the ME technique, namely the isomer shift, the magnetic hyperfine interaction and the quadrupole interaction are summarized. Further the impurity effects as the Friedel type oscillations in the charge and the RKKY type oscillations in the spin density distribution are discussed. Special attention is paid to the peculiar magnetic properties of metallic iron and its alloys. From a comparison of the magnetic hyperfine fields and bulk magnetizations as a function of the impurity concentration and from the temperature dependence of the magnetic hyperfine fields at the various sites in iron alloys, it is concluded that the 3d magnetic moments in iron are largely localized. Further the exchange interaction is provided by the remaining small percentage of itinerant 3d electrons. Finally, from a comparison of magnetic hyperfine field and isomer shift data in alloys an overall picture of the electronic changes involved in alloying has been developed.     

Fabrication and characterization of iron oxide nanoparticles filled polypyrrole nanocomposites

The effect of iron oxide nanoparticle addition on the physicochemical properties of the polypyrrole (PPy) was investigated. In the presence of iron oxide nanoparticles, PPy was observed in the form of discrete nanoparticles, not the usual network structure. PPy showed crystalline structure in the nanocomposites and pure PPy formed without iron oxide nanoparticles. PPy exhibited amorphous structure and nanoparticles were completely etched away in the nanocomposites formed with mechanical stirring over a 7-h reaction. The thermal stability of the PPy in the nanocomposites was enhanced under the thermo-gravimetric analysis (TGA). The electrical conductivity of the nanocomposites increased greatly upon the initial addition (20 wt%) of iron oxide nanoparticles. However, a higher nanoparticle loading (50 wt%) decreased the conductivity as a result of the dominance of the insulating iron oxide nanoparticles. Standard four-probe measurements indicated a three-dimensional variable-range-hopping conductivity mechanism. The magnetic properties of the fabricated nanocomposites were dependent on the particle loading. Ultrasonic stirring was observed to have a favorable effect on the protection of iron oxide nanoparticles from dissolution in acid. A tight polymer structure surrounds the magnetic nanoparticles, as compared to a complete loss of the magnetic iron oxide nanoparticles during conventional mechanical stirring for the micron-sized iron oxide particles filled PPy composite fabrication.     

Transformation of the magnetic structure of FeBO<Subscript>3</Subscript> under high pressures

The transformation of magnetic structure under hydrostatic and quasi-hydrostatic pressures up to 4 GPa was studied for iron borate FeBO₃ by the neutron diffraction method. Under quasi-hydrostatic conditions, the orientation of iron magnetic moments changes at pressures P≥1.4 GPa. Under hydrostatic conditions, no changes in the magnetic structure of iron borate were observed up to 2.1 GPa. This behavior is caused by the influence of the inhomogeneity (in magnitude and direction) of elastic stresses on the configuration of magnetic sublattices.     

Nanoparticles: Implication of Ligand Choice on Surface Properties,Crystal Structure,and Magnetic Properties of Iron Nanoparticles (Part. Part. Syst. Charact. 3/2013)

The behavior of iron nanoparticles is heavily influenced by their highly reactive surfaces. A better understanding of organic ligand/particle interactions must be achieved in order to synthesize iron nanoparticles with magnetic saturations (σ _sat) equivalent to bulk iron. Even when synthesized using careful, air‐free chemistry techniques and ligands more weakly interacting than those often reported in the literature, the magnetic saturation of iron nanoparticles generally only approaches, but not equals, the magnetic saturation of bulk iron. Here, iron nanoparticles are synthesized using Schlenk line chemistry methods and two different weakly interacting ligands: 2,4‐pentanedione and hexaethylene glycol monododecylether. These particles have saturation magnetizations slightly lower than bulk iron, which is believed to be caused by interactions between the passivating ligands and the surface of the nanoparticles. Using X‐ray absorption fine structure studies, it is shown that oxidized species of iron exist at the nanoparticles’ surface and can be attributed to iron/ligand interaction. The percentage of oxidized species scales with the surface to volume ratio of the nanoparticles, and therefore appears limited to the nanoparticle surface. X‐ray absorption fine structure analysis also shows that the nanoparticles have an expanded crystalline lattice, which can further impact their magnetic properties.     

铁芯托卡马克中二维和三维极向磁场计算模型的对比分析

为方便计算托卡马克磁场分布,建立了一些二维解析铁芯模型。由于前提假设的不同而给磁场分布的计算带来了不同的边界条件,因而得到的磁场分布计算结果与实际情况有所偏差。为了获得铁芯托卡马克的极向磁场三维分布,建立了带铁芯的极向磁场线圈三维数值模型,计算铁芯托卡马克的三维磁场,与不同铁芯模型的磁场计算结果进行比较,并且研究铁芯托卡马克的三维磁场的极向分量在环向上的不对称性。     

��о�п�����ж�ά����ά����ų�����ģ�͵ĶԱȷ���

For simplifying the calculation the magnetic distribution on tokamak, some two-dimensional analytic models including the effect of the iron core were established, such as the infinite long iron core model and the spool model. The assumptions of these two-dimensional analytic models lead to different results with the actual magnetic field due to the distinctive boundary condition. In order to accurately calculate the three-dimensional magnetic field distribution in the tokamak with iron core, a three-dimensional numerical finite element model was established based on J-TEXT tokamak. In two conditions, where the total toroidal current is nonzero or zero respectively, more comparison were carried out between the derived results of two-dimensional models and the results at different toroidal positions in three-dimensional models. Furthermore, the toroidal asymmetry of the magnetic field distribution of the three-dimensional model of tokamak with iron core was investigated. The results indicate that the three-dimensional construction of iron core causes the toroidal asymmetric poloidal magnetic field and the difference between the two- and three-dimensional models in the condition with total current of nonzero. However, in the condition with total current of zero, the intensity of toroidal asymmetric is reduced and the difference between the two- and three-dimensional models is smaller.     

Relaxation effects in Fe17 and Fe19 oxo-bridged iron clusters

The magnetic properties of a new type of iron clusters are studied by means of Mössbauer spectroscopy in an applied magnetic field. The results obtained agree with the ones obtained from magnetic susceptibility measurements. They are well explained in terms of relaxation determined by fluctuations in the hyperfine field due to spin-spin interaction. The triangular arrangement of the iron ions plays an essential role in this mechanism giving rise to spin frustration effects.