Synthesis and characterization of nickel ferrite magnetic nanoparticles

Nickel ferrite (NiFe₂O₄) nanoparticles are prepared by a polyvinyl alcohol (PVA) assisted sol-gel auto-combustion method. The structure, composition, morphology and magnetic properties of the gel precursor are characterized by powder XRD, FT-IR, TGA, HR-SEM, TEM, HR-TEM and VSM. XRD confirms the formation of single-phase nickel ferrite with space group of Fd3m and inverse spinel structure. The vibration properties of nanoparticles are analysed by FT-IR spectrum. The thermal decomposition of the gel precursors is investigated by TGA. HR-SEM and TEM images show that the particles have spherical shape with particle size in the range of ∼30 nm and consistent with XRD result. The magnetic properties of these nanoparticles are studied for confirming the ferromagnetic behaviour at room temperature.     

Electrodeposition and magnetic properties of three-dimensional bulk and shell nickel mesostructures

In this paper we demonstrate the electrodeposition of nickel, a common ferromagnetic material, in various magnetically desirable shapes including nanowires, nanoparticles and highly faceted shells. In order to obtain three dimensional mesostructures, the electrochemical deposition of nickel was performed on highly oriented pyrolytic graphite (HOPG) under different electrolyte composition and deposition potential conditions. Under potentiostatic deposition at one distinct potential negative with respect to the reversible potential of nickel, three stages of nucleation and growth take place leading to a complex morphology of deposits. However, dual-pulse potential deposition and electrodeposition in low pH solutions causing hydrogen evolution, lead to nickel deposits in the form of nanowires and nanoparticles with the complete absence of a faceted morphology. Highly faceted nickel shells were electrodeposited via a dual-bath method on prefabricated silver mesocrystals as 'template' electrodeposited on HOPG. Magnetic properties of faceted three dimensional nickel shells reveal clear signatures of facets of mesocrystals in the form of sharp steps in measured hysteresis loops and a strong magnetic anisotropy with respect to applied field direction.     

Template-free synthesis of nickel nanowires by magnetic field

Nickel nanowires were prepared by a template free method combined with chemical reduction and magnetic field. The application of an external magnetic field resulted in the formation of self-aligned metallic nickel nanowires of about 50 nm in diameter. Nickel particles were prepared in the absence of a magnetic field to better illustrate the structure directing role of the magnetic field. Physical properties of the nickel nanochains were examined by scanning electron microscopy (SEM), transmission electron microscope (TEM), X-Ray diffraction (XRD), and thermogravimetric analysis (TGA) methods. This study provides a simple method to prepare Ni nanowires in large scale which broads their practical applications.     

Synthesis and magnetic properties of nickel nanoparticles in magnesium fluoride matrix

A new composite material, comprising a diamagnetic matrix (magnesium fluoride) containing metal nanoparticles (nickel), has been synthesized in a high-vacuum laser-based universal cluster ablation system. The structure and magnetic properties of the composite were studied by transmission electron microscopy (TEM) and ferromagnetic resonance (FMR). According to TEM data, the nickel nanoparticles have a spherical shape and their dimensions are described by a narrow distribution function with an average value of 3.2 nm. An analysis of the FMR spectra reveals strong interaction between nickel nanoparticles in the composite, which accounts for an out-of-plane magnetic anisotropy and suggests the formation of granular magnetic films.     

Electrocodeposition of magnetic nickel matrix nanocomposites in a static magnetic field

The effect of an external magnetic field on the electrocodeposition of composites consisting of either Co or magnetite nanoparticles in a Ni matrix has been studied. An alkaline Ni pyrophosphate bath containing citrate was used. The magnetic particles were prepared by thermal decomposition (Co) or chemical precipitation (magnetite) and characterized by transmission electron microscopy, X-ray diffraction, dynamic light scattering, zeta potential and vibrating sample magnetometry measurements. The particle incorporation showed a distinct dependency on the orientation of an externally applied magnetic field. While the particle incorporation increased in a perpendicular field (perpendicular with regard to the electrode surface), it decreased in a parallel orientation. This result is explained with the dominating action of the magnetophoretic force. The structure and the properties of the Ni layers were significantly affected by the particle codeposition. A refinement of the Ni grains was found with increasing plating current density and as a result of the nanoparticle incorporation. The magnetic hardness and the Vickers microhardness of the films increased significantly due to the incorporation of the nanoparticles.     

聚合物保护纳米镍粉的制备与表征

采用改进的多元醇液相还原工艺,用 1,2 丙二醇作还原剂,在聚乙烯吡咯烷酮(PVP)稳定剂保护下,通过调整反应条件,在均相成核条件下,合成了粒径 25nm,具有面心立方晶体结构的纳米镍粉,运用XRD、TEM、SAED、FTIR 等微观分析手段,研究了NaOH浓度、PVP加入量等因素对制备纳米镍粉的影响。研究发现NaOH可以提高成核速率,调节颗粒生长溶质浓度,是形成粒径均匀纳米颗粒的重要条件。适量的聚合物保护剂,可以阻止成核颗粒生长,减小粒径,防止颗粒团聚,FTIR分析显示PVP分子与纳米颗粒之间存在化学作用。     

Synthesis and anomalous magnetic properties of hexagonal CoO nanoparticles

CoO nanoparticles in the 38-93 nm range have been prepared by thermal decomposition. The particles were characterized to be pyramid shape with a hexagonal close-packed structure. Their anomalous magnetic behavior includes: (i) vanishing of antiferromagnetic transition around 300 K; (ii) creation of hysteresis below a blocking temperature of 6-11 K; (iii) presence of relatively large moments and coercivities accompany with specific loop shifts at 5 K; and (iv) appearance of an additional small peak located in low field in the electron spin resonance spectrum. Further, the present results provide evidence for the existence of uncompensated surface spins. The coercivity and exchange bias decrease with increasing particle size, indicating a distinct size effect. These observations can be explained by the multisublattice model, in which the reduced coordination of surface spins causes a fundamental change in the magnetic order throughout the total CoO particle.     

Morphology-controlled fabrication and magnetic properties of nickel assemblies

In this study, nickel assemblies with various morphologies, including nanospheres, pinecone structures, microspheres, and necklace chains, were synthesized in ethylene glycol solution by adjusting the experimental conditions. We propose a possible growth mechanism for the formation of different structures, which involves the rapid nucleation of primary particles followed by slow aggregation and Ostwald ripening crystallization of the primary particles. The saturation magnetization (M_s) of the nickel assemblies decreased as the particle size declined. We found that the coercivity (H_c) of the necklace chains appeared to be higher than that of other structures due to their shape anisotropy. The results of our study indicated that the magnetic properties of the nickel assemblies were morphology-dependent. The coercivities of the nickel samples with different structures prepared in this study were two orders of magnitude higher than that of bulk nickel (0.7 Oe).     

Synthesis,thermodynamic and magnetic properties of pure hexagonal close packed nickel

A novel and fast technique for the synthesis of pure hexagonal close packed (HCP) nickel is demonstrated. The HCP nickel was electrodeposited from NiCl₂-1-ethyl-3-methylimidazolium chloride (NiCl₂-EmimCl) ionic liquid at 160 °C. X-ray diffraction confirmed the formation of pure phase. A phase transformation from HCP nickel to face centered cubic (FCC) nickel was observed at 422.6 °C and the enthalpy of transformation was found to be 16.72 J g⁻¹. The phase transformation resulted in the release of hydrogen which makes HCP nickel a potential hydrogen storage material. The electrodeposited nickel showed ferromagnetic properties and the magnetic coercivity was found to be 43 Oe.     

Synthesis and electrophoretic deposition of magnetic nickel ferrite nanoparticles

Powders with particle size ∼5–15 nm of nickel ferrite have been synthesized chemically from aqueous precursor solutions. From the structural and magnetic properties, it is determined that the synthetic material possesses high NiFe₂O₄ phase purity and controllable particle size. The optimum calcination temperature is found to be ∼500 °C, at which the NiFe₂O₄ particles exhibit a saturation magnetization of 2800 G, and a particle size of about 10 nm. The particles are then deposited onto silicon substrates by electrophoretic deposition (EPD) process. The Ni ferrite particles are suspended in a medium of isopropyl alcohol with magnesium nitrate and lanthanum nitrate salts as charging agents. The transportation of particles to the substrate surface is assisted by applied electric field and particles adhere to the substrate surface by a glycerol based surfactant. The magnetic response of the EPD film has been investigated by vibrating sample magnetometer (VSM) measurements.     

Synthesis and magnetic properties of nickel nanocrystals

Size-controlled synthesis of nickel nanocrystals by the decomposition of nickel acetylacetone in a noncoordinating reagent, oleylamine, was studied. Three processes were employed to synthesize nanocrystals with diameters in the range of 20–60 nm. The resultant nanoparticles were characterized to be single-phase nanocrystalline nickel with a face-centered cubic type. Mechanism of the size-controlled nanocrystals formation was studied and found that relative monodispersed nanocrystals could be formed by the separation of nucleation and growth process while the size could be controlled through modulating growth period. Magnetic measurements showed that samples were still ferromagnetic, and that their saturation magnetization and coercivity are size-dependent.     

Characterisation and intrinsic magnetic resonance properties of nickel nanoparticles

Nickel nanoparticles have been extensively characterised by atomic force microscopy (AFM), scanning electron microscopy (SEM) and confocal micro-Raman spectroscopy. AFM underestimates the particle size compared to SEM measurements. It is shown that Raman spectroscopy can detect the nanometre-thick NiO layer on the particles having frequency shifts of the modes indicative of phonon confinement. The magnetic properties of the particles are studied by ferromagnetic resonance (FMR) of magnetic field aligned particles. The alignment is achieved by suspending the particles in the liquid crystal MBBA and freezing the liquid in a 0.4 T DC magnetic field. The in-field solidification locks the direction of maximum magnetisation of the particles parallel to the direction of the applied DC magnetic field. This removes the effects of dynamical particle fluctuations of the nanoparticles on the magnetic properties allowing a study of the intrinsic magnetic properties of the magnetic nanoparticles. The intensity of the FMR signal decreased with lowering temperature for the particles frozen in the liquid in a 0.4 T DC magnetic field. The effect is suggested to be due to a reduction of the microwave skin depth with lowering temperature.     

Effect of magnetic nanoparticles on the properties of magnetic rubber

A new kind of magnetic rubber was prepared through conventional rubber mixing techniques on a two-roll mill, in which the magnetic filler was Fe₃O₄ nanoparticles and was surface modified. The effect of Fe₃O₄ nanoparticles’ content on the mechanical and magnetic properties of nature rubber was further investigated. The obtained results of six different compositions for nature rubber with 0, 5, 10, 15, 20 and 25 phr of Fe₃O₄ nanoparticles were compared. It was found that the magnetic rubber has higher magnetic properties and tensile strength, comparing with unfilled nature rubber. The result suggests that when the magnetic filler is nanoparticles and surface modified, the mechanical and magnetic properties of the rubber can be synchronously improved, which is difficult to be observed in previous work.     

Electrodeposition of macroporous magnetic metal films using colloidal nickel phosphate templates

Two-dimensional (2D) and three-dimensional (3D) macroporous nickel based films with randomly distributed spherical pores (diameter 90-210 nm) were synthesized by a simple templated electrodeposition route. Porous templates on Sn doped In₂O₃ (ITO) coated glass were constructed via electrophoretic deposition (EPD) of colloidal nickel phosphate particles prepared by a homogeneous precipitation method. The infilling of metal was sequently carried out in an electrodeposition bath, and porous films were obtained by dissolving the templates in ammonium sulfate solution. By adjusting the deposition charge, the thickness of the porous films could be controlled from 100 nm to tens of microns. Room temperature magnetic properties of the porous films were studied, remarkably enhanced coercivity and squareness than that of corresponding plain films were observed.     

Observation of magnetic, structural and surface morphological studies of triangle-like nickel nanoplates

Two-dimensional triangle-like nickel nanoplates have been synthesized by solvothermal method in the presence of triethylamine as a structure directing agent. The structure, morphology and magnetic properties of the as-synthesized products were characterized by X-ray diffraction, Atomic force microscopy and Superconducting quantum interference device magnetometer. The as-synthesized products have been confirmed to be phase-pure crystalline nickel with face centered cubic structure on the basis of X-ray diffraction characterization. Atomic force microscopy image demonstrated that the as-prepared nickel product possess two-dimensional triangle-like structure with edge length of about 65-85 nm. Magnetic measurements showed that the coercive forces at 4.2 K and 300 K for nickel nanoplates are 363.3 and 182 Oe, respectively. The nickel nanoplates exhibit a distinct enhanced coercive force due to the presence of shape anisotropy when compared with that of bulk. A possible mechanism for the formation of triangle-like Ni nanoplate structure is proposed.     

Effect of silica-coating on crystal structure and magnetic properties of metallic nickel particles

The development of a simple method that perfectly controls the oxidation and aggregation of metallic particles has been performed. In the present work, metallic nickel (Ni) particles were used as a control, and silica-coating of them was performed to control oxidation and aggregation of them. Metallic Ni particles with a particle size of 924.1 ± 315.7 nm were synthesized in water and exposed to air. Nickel(II) acetate tetrahydrate, hydrazine, and poly(sodium 4-styrenesulfonate) were used as the Ni source, reducing reagent, and stabilizer, respectively. Silica-coating of the metallic Ni particles was performed by adding tetraethylorthosilicate/(3-aminopropyl)triethoxysilane/ethanol solution to the metallic Ni particle colloid solution (Ni/SiO₂). The uncoated metallic Ni particles and metallic Ni in the Ni/SiO₂ particles began to be oxidized while annealing in air to form NiO at 400 and 500 °C, respectively; the oxidation of metallic Ni particles was controlled by the silica coating. The Ni/SiO₂ particles prepared and annealed at 100–300 °C showed soft magnetic behavior, and the saturation magnetization of g-Ni was almost comparable to that of bulk metallic Ni. In addition, the Ni/SiO₂ particles annealed even at 500 °C still had soft magnetic behavior, which also supported that the oxidation of metallic Ni particles was successfully controlled by the silica coating.     

Synthesis of nickel nanoparticles with uniform size via a modified hydrazine reduction route

Well dispersed nickel nanoparticles with uniform size were synthesized via a modified hydrazine reduction route without any surfactant introduced. Ethanol was used as solvent and played the complementary reducing role. The as-prepared samples were characterized by XRD, FESEM, TEM and TG. Pure metallic Ni could be easily obtained when ethanol instead of water was used as solvent. The particle surface was much improved when ethanol was involved in the reduction process at high temperature. The resultant particles have smooth surface and uniform size of about 50 nm. The nickel powders have an oxidization temperature of about 200 °C. The formation process was discussed based on the experimental results.     

Structural and magnetic properties of Mn nanoparticles prepared by arc-discharge

Mn nanoparticles are prepared by arc discharge technique. MnO, α-Mn, β-Mn, and γ-Mn are detected by X-ray diffraction, while the presence of Mn₃O₄ and MnO₂ is revealed by X-ray photoelectron spectroscopy. Transmission electron microscopy observations show that most of the Mn nanoparticles have irregular shapes, rough surfaces and a shell/core structure, with sizes ranging from several nanometers to 80 nm. The magnetic properties of the Mn nanoparticles are investigated between 2 and 350 K at magnetic fields up to 5 T. A magnetic transition occurring near 43 K is attributed to the formation of the ferrimagnetic Mn₃O₄. The coercivity of the Mn nanoparticles, arising mainly from Mn₃O₄, decreases linearly with increasing temperature below 40 K. Below the blocking temperature T_B ≈ 34 K, the hysteresis loops exhibit large coercivity (up to 500 kA/m), owing to finite size effects, and irreversibility in the loops is found up to 4 T, and magnetization is not saturated up to 5 T. The relationship between structure and the magnetic properties are discussed.     

Microwave-assisted synthesis of nickel nanoparticles

Nickel nanoparticles with uniform, monomorphic self-assembled flower-like microstructure were synthesized by reduction of nickel chloride with hydrazine hydrate in the presence of polyvinylpyrrolidone (PVP) in ethylene glycol under microwave irradiation. An appropriate amount of Na₂CO₃ was necessary for the formation of monomorphic and uniform Ni nanoflowers. Small amount of NaOH and a higher concentration of hydrazine were beneficial to the formation of Ni nanoflowers with a smaller diameter and a narrower distribution. The transmission electron microscopy (TEM) and X-ray diffraction measurements manifested that the as-synthesized Ni nanoflower was the assembles self-organized by hundreds of smaller primary nanoparticles with an average dimension of about 6.3 nm.     

锰锌铁氧体纳米粒子的制备和磁性能研究

以金属离子的硫酸盐溶液和氨水溶液为原料,采用水热法制备了粒径为6～16nm的锰锌铁氧体纳米粒子.采用XRD、TEM、TGA和VSM等方法对产物以及产物的磁性能进行了表征.结果表明,锰锌铁氧体(Mn1-xZnxFe2O4)的居里温度随着锌的相对含量x的增加而单调的降低.锰锌铁氧体的磁化强度先随着锌的相对含量x的增加而增大,当锌的相对含量＞0.6时,磁化强度随着锌的相对含量x的增加而减小.测量了锰锌铁氧体磁流体的饱和磁化强度,计算了锰锌铁氧体(Mn0.4Zn0.6Fe2O4)纳米粒子的磁矩,其值为1.01×10-19A·m2.