Magnetic Properties of Ball-Milled Nanocrystalline Alloys Fe78B13Si9

Summary.  Magnetic properties of nanocrystalline Fe₇₈B₁₃Si₉ alloys are studied for three series prepared by ball milling starting from amorphous ribbons, crystallized ribbons, and elemental powders. Temperature variation of static magnetization results in strong ferromagnetic interaction which is weakly dependent on the initial material. Magnetic hysteresis loops show that saturation magnetization, magnetic remanence, and coercive field increase with frequency for both series of ribbon samples, whereas they decrease for alloys prepared from elemental powders. Power losses raise faster for the alloys prepared from elemental powders than for the two other alloys. Received October 5, 2001. Accepted (revised) November 12, 2001     

Microstructure and Magnetic Behaviour of Nanosized Fe<Subscript>3</Subscript>O<Subscript>4</Subscript> Powders and Polycrystalline Films

Summary.  The object of investigation were the magnetic interactions in nanostructured Fe₃O₄ assemblies of two kinds (powder and film) where particles of similar size present nearly uniform domains in a close to planar arrangement with spacings sufficient for magnetic interactions. We discuss the use of the soft-chemistry method, i.e. the modified ‘ferrite plating’ (MFP) technique, for the synthesis of polycrystalline films of magnetite with nanosized crystallites. Received October 22, 2001. Accepted January 21, 2002     

Self-Organization of Magnetic Nanoparticles and Inclusion of Hydrogen by Borohydride Reduction

Summary.  Different structures of the interglobular space or voids between self-organized nanoparticles lead to differences in the measurable magnetic properties of single-domain particle chains of similar composition, grain size, and amorphous structure of the single globules. The volumes and radii of nanoparticles obtained by application of a magnetic field (3 to 15 nm) are larger than those determined without application of a magnetic field during the borohydride reduction process. Two types of hydrogen containing nanotubes with diameters of up to 2 (small-size containers) and 5 nm (large-size containers) are produced using as a driving force the domain wall formation energy between ferromagnetic nanoparticles with quantum size effected dimensions prepared by this reduction method at room temperature and ambient atmosphere. Nanoscale hydrogen containers can be used instead of MeH nanoparticle electrodes as perfect energy charge transfer media of high efficiency (close to 100%) using Li ion electrolytes. No influence on the electrode temperature and no participation of OH⁻ and H₂O in the main charge/discharge transfer reactions were observed. Received October 25, 2001. Accepted (revised) January 3, 2002     

Electronic Structure and Size of TiO2 Nanoparticles of Controlled Size Prepared by Aerosol Methods

Summary.  A complete characterization of nanostructures has to deal both with electronic structure and dimensions. Here we present the characterization of TiO₂ nanoparticles of controlled size prepared by aerosol methods. The electronic structure of these nanoparticles was probed by X-ray absorption spectroscopy (XAS), the particle size by atomic force microscopy (AFM). XAS spectra show that the particles crystallize in the anatase phase upon heating at 500°C, whereas further annealing at 700°C give crystallites of 70% anatase and 30% rutile phases. Raising the temperature to 900°C results in a complete transformation of the particles to rutile. AFM images reveal that the mean size of the anatase particles formed upon heating at 500°C is 30 nm, whereas for the rutile particles formed upon annealing at 900°C 90 nm were found. The results obtained by these techniques agree with XRD data. Received October 5, 2001. Accepted (revised) December 6, 2001     

Influence of Al2O3 Nanoparticles on the Thermal Stability of Ultra-Fine Grained Copper Prepared by High Pressure Torsion

Summary.  Ultra-fine grained (UFG) Cu (grain size 80 nm) containing 0.5 wt.% Al₂O₃ nanoparticles (size 20 nm) was prepared by high pressure torsion (HPT). Positron lifetime spectroscopy was employed to characterize the microstructure of this material, especially with respect to types and concentration of lattice defects. The evolution of microstructure with increasing temperature was studied by positron lifetime spectroscopy and X-ray diffraction measurements. The thermal stability of the Cu + 0.5 wt.% Al₂O₃ nanocomposite was compared with that of pure UFG Cu prepared by the same technique. The processes taking place during thermal recovery of the initial nanoscale structure in both studied materials are described. Received October 5, 2001. Accepted (revised) December 20, 2001     

Influence of Nanoporosity and Roughness on the Thickness-Dependent Coercivity of Iron Nanonetworks

Summary.  We have studied the coercivity of magnetic nanonetworks as a function of thickness, nominal pore diameter, and surface/interface roughness in the thickness range of approximately 2 to 45 nm where a Néel-type domain wall has been theoretically predicted. Such magnetic nanonetworks have been prepared by sputtering iron on the walls of commercially available porous nano-channel alumina (NCA) membranes. The thickness dependence of coercivity has also been studied on films deposited on surface-oxidized Si and glass subtrates. These substrates are essentially non-porous and much smoother than NCAs. Our investigation shows that the coercivity of films deposited on Si and glass depends on the spatial fluctuation of thickness which arises from the roughness of the apparently smooth substrates. On the other hand, NCAs are found to be inherently quite rough, and films on NCAs show a complex thickness dependence which arises from the interplay between surface/interface roughness, domain pinning due to porosity, surface anisotropy, surface torques, and oxidation of the iron films. It was found that the growing films on NCA substrates led to partial filling up of the pore entrance, thereby reducing its effective diameter. The film growth also affects the roughness of the film, which in turn affects its coercivity. We propose a model for the thickness dependence of coercivity based on the pore fill-up geometry considering the effective pore diameter and the critical thickness at which the pore will be completely filled up. Experimental results on coercivity with thickness variation of iron network deposited on NCA generally agree with the suggested model. Received October 16, 2001. Accepted (revised) January 11, 2002     

Structure and Magnetic Properties of Nickel–Zinc Ferrite Nanoparticles Prepared by Glass Crystallization Method

Summary. The magnetic and microstructure properties of Fe₂O₃–0.4NiO–0.6ZnO–B₂O₃ glass system, which was subjected to heat treatment in order to induce a magnetic crystalline phase (Ni_0.4Zn_0.6-Fe₂O₄ crystals) within the glass matrix, were investigated. DSC measurement was performed to reveal the crystallization temperature of the prepared glass sample. The obtained samples, produced by heat treatment at 765°C for various times (1, 1.5, 2, and 3 h), were characterized by X-ray diffraction, IR spectra, transmission electron microscopy, and vibrating sample magnetometer. The results indicated the formation of spinel Ni–Zn ferrite in the glass matrix. Particles of the ferrite with sizes ranging from 28 to 120 nm depending on the sintering time were observed. The coercivity values for different heat-treatment samples were found to be in the range from 15.2 to 100 Oe. The combination of zinc content and sintering times leads to samples with saturation magnetization ranging from 12.25 to 17.82 emu/g.     

Magnetic Co3O4 nanowires,preparation and properties

The Co₃O₄ nanowires have been successfully synthesized via modified template method.The as-prepared products have been characterized by EDS,TEM and HRTEM analysis.The magnetic behavior of it is investigated by a magnetic property measurement system.The nanowires exhibit some novel magnetic properties,which are different from its bulk material.The temperature dependence curves of magnetization in zero-field-cooling and field-cooling exhibit two peaks of antiferromagnetic at blocking temperature of～23 K and～31 K,respectively.The field dependent M（H） curves of the Co₃O₄ nanowires at T = 5 and 300 K both exhibit PM properties.Moreover,the diameter of nanowires is hence determined according to the finite size effect as approximately 7-11 nm,in consistent with the characterizations by HRTEM.     

磁性纳米颗粒在生物医学领域中的应用

磁性纳米颗粒作为一种新型纳米材料,在许多领域,特别是在生物医药、生物工程等方面具有广阔的应用前景.本文着重论述了近年来磁性纳米颗粒在生物分离、靶向给药、热疗以及磁共振成像对比剂等方面的应用,并对其应用前景进行了展望.     

Preparation of Nanostructured Magnetic Films by the Plasma Jet Technique

Summary.  Magnetic films were prepared by the plasma jet technique from Fe, mumetal, and Fe/Hf or Fe/Ta nozzles. Two different plasma jet systems with different vacuum pumps were used to compare the quality of the produced films. The films prepared from a Fe nozzle in the two different equipments shows that oxygen in the residual atmosphere of the low vacuum reactor leads mainly to the formation of iron oxides. The Fe and mumetal films prepared in the high vacuum system contain only a very small amount of oxygen, as proved by chemical analysis and ferromagnetic resonance. The mumetal film, moreover, shows good soft magnetic properties and low magnetic damping. For the reactive plasma jet deposition of nanogranular Fe–Hf–O and Fe–Ta–O films, the low vacuum system was used. The films with higher oxygen content exhibit tunneling-type conductivity. In some films, superparamagnetic behaviour and spin-dependent tunneling magnetoresistance were observed. Received October 5, 2001. Accepted November 22, 2001     

EXAFS Investigations on Nanocomposites Composed of Surface-Modified Zirconium and Zirconium/Titanium Mixed Metal Oxo Clusters and Organic Polymers

Summary.  The surface-modified oxometallate clusters Zr₆(OH)₄O₄(OMc)₁₂, Ti₄Zr₄O₆(OBu)₄ (OMc)₁₆, and Ti₂Zr₄O₄(OBu)₂(OMc)₁₄ (OMc = methacrylate) as well as their nanocomposites with polystyrene, poly(methacrylic acid) and poly(methyl methacrylate) were investigated by EXAFS. Studies on the nanocomposites revealed that the structure of the cluster core is retained in the hybrid materials. Received October 23, 2001. Accepted November 12, 2001     

Thermochromism and Solvatochromism in Solution

Summary.  The thermochromic behaviour of various coordination compounds in solution is discussed, with a special focus on cyclic diamine chelates. Thermally induced spin-crossover phenomena of iron(II) complexes are also considered. The solvatochromic behaviour of mixed-ligand complexes is presented in detail. Received April 2, 2001. Accepted (revised) April 19, 2001     

A Phenyl α-Nitronyl Nitroxide with a Forced Chiral Conformation

Summary.  A new phenyl α-nitronyl nitroxide bearing a hydroxyl group at position 2 of the aromatic ring and a chiral methyl lactate substituent at position 5 has been synthesized with the aim of combining the magnetic properties of this kind of radical with the optical properties endowed by the chiral group. The optically active compound forms intramolecular hydrogen bonds between the OH group and one of the NO groups and shows a large torsion angle between the two rings when compared with similar radicals with no substituent in this position. Therefore, the optical properties are distinct. The optical and magnetic properties of the new radical in both solution and solid state are presented. Received June 23, 2000. Accepted (revised) September 18, 2000     

Inorganic Clusters in Organic Polymers and the Use of Polyfunctional Inorganic Compounds as Polymerization Initiators

Summary.   Silicon oxide or metal oxide clusters or small particles with polymerizable organic groups covalently bonded to their surface can be copolymerized with organic monomers by various polymerization techniques. Whereas the preparation and properties of the polymers reinforced by R ₈Si₈O₁₂ have already been well investigated, analogous materials with incorporated transition metal oxide clusters are only beginning to show their potential as an interesting new class of inorganic-organic hybrid polymers. In the second part of the article, approaches are reviewed in which the inorganic building block serves as an initiator for polymerization reactions. This results in materials in which the organic polymer is grafted from an inorganic core. Most work has been done with surface-modified silica particles. Free radical polymerizations and atom transfer radical polymerizations with macroinitiators are summarized. The latter method results in polymeric particles in which an inorganic core is surrounded by an organic polymer shell. A new approach is the use of polyfunctional inorganic molecules or molecular clusters as initiators. Received July 28, 2000. Accepted August 7, 2000     

Different methods for the fractionation of magnetic fluids

 Magnetic fluids are used in many fields of application, such as material separation and biomedicine. Magnetic fluids consist of magnetic nanoparticles, which commonly display a broad distribution of magnetic and nonmagnetic parameters. Therefore, upon application only a small number of particles contribute to the desired magnetic effect. In order to optimize magnetic fluids for applications preference is given to methods that separate magnetic nanoparticles according to their magnetic properties. Hence, a magnetic method was developed for the fractionation of magnetic fluids. Familiar size-exclusion chromatography of two different magnetic fluids was carried out for comparison. The fractions obtained and the original samples were also magnetically characterized by magnetic resonance and magnetorelaxometry, two biomedical applications. The size-exclusion fractions are similar to those of magnetic fractionation, despite the different separation mechanisms. In this respect, magnetic fractionation has several advantages in practical use over size-exclusion chromatography: the magnetic method is faster and has a higher capacity. The fractions obtained by both methods show distinctly different magnetic properties compared to the original samples and are therefore especially suited for applications such as magnetorelaxometry. Received: 12 July 1999/Accepted in revised form: 9 November 1999     

Two Novel Er-Cr Ion-Pair Complexeswith Hydrogen Bonding Network: Syntheses, Crystal Structures, and Magnetic Properties

Summary.  Two novel Er-Cr ion-pair complexes ([Er(DMA)₃(H₂O)₄][Cr(CN)₆] and [Er(MPL)₄(H₂O)₃][Cr(CN)₆]·2H₂O; DMA = dimethylacetamide, MPL = 1-methyl-2-pyrrolidinone) have been synthesized. [Er(DMA)₃(H₂O)₄][Cr(CN)₆] crystallizes in the monoclinic system (space group P _c ) with a = 9.789(2), b = 11.263(2), c = 13.997(3)?, β = 105.66(3)°, V = 1485.9(5)?³, Z = 2; [Er(MPL)₄(H₂O)₃][Cr(CN)₆]·2H₂O crystallizes in the monoclinic system (space group P2₁) with a = 9.447(2), b = 13.881(3), c = 14.673(3)?, β = 101.85(3), V = 1883.1(7)?³, Z = 2. X-Ray crystal diffraction analyses reveal that the two complexes form a hydrogen bonding network structure through the CN group and H₂O molecules. Variable temperature susceptibilities for the two complexes indicate that weak antiferromagnetic interactions exist between cation and anion pairs through this hydrogen bonding network.     

磁性纳米颗粒Pt3Co的制备与性质研究

利用乙二醇还原法合成了Pt3Co磁性纳米颗粒，利用TEM、TG－DTA和磁滞回线的测量对其进行表征，结果表明，纳米颗粒的平均粒径为2.3nm，且粒径分布较窄，具有较高的矫顽力。     

三氧化二砷磁性纳米粒的表征及其在小鼠组织中的药代动力学

通过溶剂转移法制备了三氧化二砷铁氧体磁性纳米粒(As₂O₃-MNPs). 利用扫描电镜/能谱分析、红外光谱(IR)和差示扫描量热法(DSC)等技术对其进行了表征. 选择正常小鼠肝脏作为靶区, 在外加磁场的诱导下, 考察As₂O₃-MNPs在小鼠体内的组织药代动力学特征, 以此反映该磁性纳米粒的磁靶向性效果. 红外光谱分析结果显示, As₂O₃-MNPs中存在磁性材料MgFe₂O₄; DSC分析表明, 制备磁性纳米粒所用材料As₂O₃、乳酸羟基乙酸共聚物(PLGA)和铁氧体之间没有明显的相互作用, 可用于磁性纳米粒的制备; 能谱分析结果显示As₂O₃和磁性材料MgFe₂O₄ 不是吸附于纳米粒的表面, 而是包裹于其中; 磁场组小鼠肝脏组织中药物浓度-时间曲线下面积(AUC_0-∞)、达峰浓度(c_max)和消除半衰期(t_1/2)均明显大于非磁场组(P<0.05), 说明As₂O₃-MNPs在正常小鼠体内有良好的磁靶向性分布. 所制备的三氧化二砷磁性纳米粒稳定性好, 靶向性强, 在肿瘤治疗方面具有良好的应用前景.     

DNA Hybridization at Magnetic Nanoparticles with Electrochemical Stripping Detection

A simple and practical method for electrochemical DNA hybridization assay has been developed to take advantage of magnetic nanoparticles for ssDNA immobilization and zinc sulfide nanoparticle as oligonucleotide label. Magnetic nanoparticles were prepared by coprecipitation of Fe²⁺ and Fe³⁺ with NH₄OH, and then amino silane was coated onto the surface of magnetite nanoparticles. The magnetic nanoparticles have the advantages of easy preparation, easy surface modification and low cost. The target ssDNA with the phosphate group at the 5′ end was then covalently immobilized to the amino group of magnetite nanoparticles by forming a phosphoramidate bond in the presence of 1‐ethyl‐3‐(3‐dimeth‐ylaminopropyl)carbodiimide (EDAC). The zinc sulfide (ZnS) nanoparticle‐labeled oligonucleotides probe was used to identify the target ssDNA immobilized on the magnetic nanoparticles based on a specific hybridization reaction. The hybridization events were assessed by the dissolution of the zinc sulfide nanoparticles anchored on the hybrids and the indirect determination of the dissolved zinc ions by anodic stripping voltammetry (ASV) at a mercury film glassy carbon electrode (GCE). The proposed method couples the high sensitivity of anodic stripping analysis for zinc ions with effective magnetic separation for eliminating nonspecific adsorption effects and offers great promise for DNA hybridization analysis.