One step production of magnetic nanoparticle films by laser pyrolysis inside a chemical vapour deposition reactor

Deposition of nanoparticulated films onto glass has been achieved by using an unprecedented combination of laser pyrolysis and chemical vapour deposition (CVD) on a single step process. Characterisation of the films reveals that the coated glasses obtained by this technique have similar characteristics to the ones previously fabricated using a two step pyrolysis plus CVD process. Under the laser action, maghemite or hematite nanoparticulated coatings are obtained by varying the processing conditions. We envisage the incorporation of this one step process for industrial production, where the nanoparticulated film would be deposited as the glass moves along the production line.     

Compositional optimization of magnetite thin films prepared by rf sputtering from a composite target of wüstite and Ge

This study investigated the compositional optimization of magnetite (Fe₃O₄) thin films containing a small amount of Ge to enhance magnetization. No substrate bias was applied during deposition. In a pure Ar atmosphere, the film structure changed from the phase mixture of magnetite and wüstite (Fe_1 − xO) to the weak appearance of wüstite with increasing Ge content. The antiferromagnetic wüstite thus obtained was employed as a starting material to prepare single-phase magnetite, and a gas mixture of Ar and O₂ was then applied. Single-phase magnetite thin films exhibit ferrimagnetic behavior with maximum magnetization of 0.42 T at 1196 kA m⁻¹(15 kOe), which exceeds that of a composite target of ceramic magnetite with Ge chips. Simultaneously adding Ge to the iron-excess wüstite target therefore effectively enhanced magnetization.     

Strain effects and phase separation tendency in highly strained La0.7Ba0.3MnO3 thin films on LaAlO3 substrates

The magnetic and transport properties of epitaxial La_0.7Ba_0.3MnO₃ films on LaAlO₃ substrates have been investigated and compared with those on SrTiO₃ substrates. It is found that the ferromagnetic and metallic transition temperature of the highly compressive strained films on LaAlO₃ substrates decreases steadily with decreasing film thickness, while it changes little in the lightly strained films on SrTiO₃ substrates. The properties of the films on LaAlO₃ substrates are more sensitive to a post-annealing procedure. A tendency to phase separation, which induces a difference between the insulator-metal transition temperature T_MI and the Curie temperature T_C, is observed for the films with a medium oxygen annealing process. We argue that the phase separation is due to both the highly compressive strain and oxygen deficiency in the films.     

Domain wall generation and propagation in an amorphous ferromagnetic NiFeSiB film confirmed by the magneto-optical indicator film method

We employed the magneto-optical indicator film method to observe domain wall generation and propagation in NiFeSiB thin films. This method is sensitive to the magnetization directions on both surfaces as well as in the interior of the film. NiFeSiB has a lower magnetic anisotropy value compared to that of the CoFe and, therefore, it contains thicker domains. As an external magnetic field is strengthened, an increasing number of domains are generated and propagated into the interior. The use of a synthetic antiferromagnet layered structure leads to a reduction in both the value of the switching field and the number of domains generated as compared with the NiFeSiB single layer case, resulting from a reduction in the magnetostatic energy.     

难选赤褐铁矿焙烧-磁选试验研究

对某含铁品位为45％、磁性率（FeO／TFe）为2．7％的难选赤褐铁矿矿石进行了选矿试验研究，考查了该矿石的矿物工艺学和磨矿特性，重点研究了强磁选、还原焙烧-磁选分选情况，确定还原焙烧-磁选可以获得较好的选别指标为：精矿铁品位达60％以上，产率达85％以上，铁回收率90％以上，尾矿铁品位下降到15％以下。     

Magnetic properties of thermal plasma synthesized nanocrystalline nickel ferrite (NiFe2O4)

A rapid synthesis method is reported for magnetic nanoparticles of nickel ferrite involving thermal plasma assisted vapor phase condensation process. The as-synthesized samples were characterized by X-ray Diffraction, Transmission Electron Microscopy, Vibrating Sample Magnetometer and X-ray Photoelectron Spectroscopy techniques. The average particle size was determined from the TEM micrographs and found to be around 30 nm. The effects of reactor parameters on the magnetic and structural properties have been evaluated, to find the optimized parameters so as to achieve the highest values of saturation magnetization and coercivity. Reasonably high saturation magnetization (48 emu/g) has been assigned to the high degree of crystallinity, achieved on account of high temperature during the growth, and the cation redistribution. The high value of coercivity (115 Oe) is explained on the basis of possible lattice defects arising from the cation redistribution. Detailed analysis of cation distribution using the XRD line intensity data leads to the conclusion that these samples are iron deficit and nickel rich.     

大间隙磁性液体静密封研究

为满足航空、航天、冶金等领域大间隙静密封要求,建立磁性液体静密封试验台,设计出磁性液体静密封试验件。在试验台上对磁性液体静密封进行深入研究,通过试验得出磁性液体静密封耐压、磁性液体注入量与密封间隙、密封温度和磁性液体磁化强度的关系。从理论上,计算试验件密封间隙中磁场分布,推导出磁性液体静密封耐压和温度关系的解析表达式,计算磁性液体静密封在不同间隙,不同饱和磁化强度下的最大耐压能力。理论分析和试验表明,在大间隙下磁性液体静密封能够满足一定耐压要求,具有实用价值。     

Rietveld refinement,Raman, optical,dielectric, Mössbauer and magnetic characterization of superparamagnetic fcc-CaFe2O4 nanoparticles

This article describes synthesis of superparamagnetic fcc-CaFe₂O₄ nanoparticles by a metal nitrate-citrate monohydrate sol–gel route and characterization using X-ray diffractometry, Raman spectroscopic, UV–Vis–NIR optical absorption spectroscopic, Mössbauer spectroscopy, dielectric and SQUID magnetometry measurements. Rietveld refinement of the X-ray diffraction pattern and observation of active A_1?g, T_2?g & E_g modes in the Raman spectrum confirmed formation of single phase CaFe₂O₄ nanoparticles in the spinel ferrite type fcc structure without impurity. Mössbauer and Rietveld data analysis revealed that nanocrystalline CaFe₂O₄ is dominantly an inverse ferrite in which 85% Ca atoms preferentially occupy the octahedral site in the fcc symmetry and the Fe ions are in high spin Fe⁺³ state. Nanocrystalline CaFe₂O₄ significantly absorbs optical light below 500?nm and the direct band gap energy is estimated to ~1.83?eV, which is higher than 1.26?eV reported for orthorhombic CaFe₂O₄. Temperature and field dependent magnetic studies showed that fcc-CaFe₂O₄ nanoparticles exhibit superparamagnetism at room temperature with high saturation magnetization of 1.07μ_B. The blocking temperature is ~53?K at 1000?Oe and ~72?K at 500?Oe clearly shows lowering of blocking temperature at higher magnetic field. Interestingly below the blocking temperature at 20?K, CaFe₂O₄ nanoparticles behave as non collinear soft-ferrimagnetic material with a saturation magnetization of 1.16 μ_B, coercivity of 150?Oe and remanence of 4.45?emu/g. The magnetic momenta of Fe⁺³ ions residing at the octahedral sub-lattice are canted at ~25?°.     

Tungsten-substituted double perovskite Ba2FeMo1-xWxO6 for enhanced magnetocaloric effects

Double perovskite materials Ba₂FeMo_1-xW_xO₆ (0.0 ≤ x ≤ 0.4) partially substituted with Tungsten (W) at the Molybdenum (Mo) site were prepared by the solid state reaction method and thoroughly investigated for structural, magnetic and magnetocaloric properties. Rietveld refined X-ray diffraction profiles were used to confirm the formation of cubic structure with Fm-3m space group in both the pristine as well as W-substituted samples. Upon increasing temperature, a single magnetic transition from ferromagnetic to paramagnetic phase was observed in each sample at its Curie temperature around which maximum magnetic entropy change could be obtained. A second order nature of the magnetic phase transition was established in all the samples with the help of Arrott plots and the universal master curve investigations and the magnetocaloric effect was obtained from the magnetic isotherms. Magnetocaloric effects estimated in terms of the maximum magnetic entropy change and temperature averaged entropy change (TEC) were enhanced with controlled W-substitution. Among the various compositions, sample with (x = 0.3) i.e., Ba₂FeMo_0.7W_0.3O₆ demonstrated a magnetic entropy change of 1.483 J/kgK and a TEC value of 2.74 J/kgK over a temperature span of 10 K under an applied magnetic field of 2.5 T. The results obtained in the present work clearly suggest that the investigated compounds can be customized for use in magnetic refrigeration technology.     

Morphology- and magnetism-controlled electrodeposition of Ni nanostructures on TiO2 nanotubes for hybrid Ni/TiO2 functional applications

We investigate magnetic properties of nickel nanoparticles electrodeposited on TiO₂ nanotubes by different techniques including direct current (DC) and cyclic voltammetry (CV) deposition. TiO₂ nanotubes were fabricated by anodic oxidation from an organic electrolyte under constant voltage on Ti substrates. Using scanning and transmission electron microscopies, we observe that each technique provides different morphologies: DC electrodeposition makes large coalesced Ni nanoparticles mostly accumulated on top surface and mouths of the nanotubes, whereas CV deposition produces a homogenous dispersion of Ni nanoparticles across the nanotubes. The variation of coercivity and saturation magnetization values recorded is consistent with our scenario, though owing to large number of nanoparticles with size and shape varieties. The first order reversal curve (FORC) diagrams help to reveal the magnetic behavior of nanoparticle ensembles in relation to their morphology and crystal structure.