Ferromagnetic Ni Nanoparticles Research Articles

Ferromagnetic Ni Nanoparticle with Controlled Anisotropy: From Polyhedral to Planar Tetrapods

Liquid phase syntheses mainly yield nanoparticles with compact shapes, such as spheres or cubes. However, controlling not only the size but also the shape of magnetic nanoparticles would enable a fine-tuning of their intrinsic properties, due to the shape anisotropy induced by long-range dipolar interactions. We report here a fairly simple approach based on the reduction of an amidinate complex in the presence of a mixture of long-chains acid and amine to yield ferromagnetic Ni nanoparticles. The formation of stable Ni complexes could be promoted in situ by increasing the acid concentration, thus allowing tuning of the final particle size. While amine could be used as a soft reducing agent, dihydrogen was essential to promote anisotropic shapes. Electron holography combined with micromagnetic simulations showed that the resulting shape anisotropy could impose complex magnetic configurations within planar tetrapods. Regarding the heating efficiency, which directly scales with the magnetic hysteresis loop area, maxima of 100W·g–1 were found for nanoplates and nanorods, opening promising perspectives for magnetically induced catalysis.

Electrochemical Deposition of Ferromagnetic Ni Nanoparticles in InP Nanotemplates Fabricated by Anodic Etching Using Environmentally Friendly Electrolyte.

Porous InP templates possessing a thickness of up to 100 µm and uniformly distributed porosity were prepared by anodic etching of InP substrates exhibiting different electrical conductivities, involving an environmentally friendly electrolyte. Ni nanoparticles were successfully directly deposited by pulsed electroplating into prefabricated InP templates without any additional deposition of intermediary layers. The parameters of electrodeposition, including the pulse amplitude, pulse width and interval between pulses, were optimized to reach a uniform metal deposition covering the inner surface of the nanopores. The electrochemical dissolution of n-InP single crystals was investigated by measuring the current-voltage dependences, while the Ni-decorated n-InP templates have been characterized by scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDX). The proposed technology is expected to be of interest for sensing and photocatalytic applications, as well as for the exploration of their plasmonic and magnetic properties.

Synthesis and characterization of the novel nanostructured NiC carbide obtained by mechanical alloying

In the present work, a comprehensive study of mechanical alloying of Ni-carbon nanotubes (CNT) and Ni-Graphite equiatomic powder mixtures under the same technological modes has provided to reveal the features of using different types of carbon (CNT or graphite) as a charge component. The as-milled powders were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD) and magnetometric study. A novel nanoscale fcc NiC monocarbide was synthesized regardless the type of the charge used. According to the XRD study the formation of this phase takes place in two stages. A two-step carbide formation mechanism has been proposed. The associated changes in the nickel lattice, such as changes in the lattice parameter, lattice strain and residual stresses, which led to the formation of NiC monocarbide were also evaluated and discussed. Parameters of the electronic structure of NiC were calculated using the MStudio MindLab 7.0 software package with the experimental data on the crystal structure of the NiC phase obtained as input. Temperature dependencies of magnetic susceptibility of NiC synthesized have been studied up to 950 K. Carbides synthesized were found to be weak ferromagnets at the room temperature and their Curie temperature TC ranges within 670 – 725 K. The calculated value of the magnetic moment per nickel atom (2.83μB) is higher than that of a bulk Ni (1.3μB). Likely, the observed increase of μ is caused by the presence of a certain amount of residual single-domain ferromagnetic Ni nanoparticles in the samples synthesized.

Single particle inductively coupled plasma mass spectrometry with and without flow injection for the characterization of nickel nanoparticles

This work compares the performance of transmission electron microscopy (TEM), scanning electron microscopy (SEM), X-ray diffraction (XRD), single particle inductively coupled plasma mass spectrometry (spICPMS) and flow injection (FI) coupled to spICPMS for the characterization of synthetic ferromagnetic Ni nanoparticles (NPs) prepared with and without polyvinylpyrrolidone (PVP) stabilizer. Whereas single NPs measurement by XRD yielded nominal diameters of 13.7 and 16.6 nm with and without PVP respectively, a diameter of 100–130 nm was obtained by TEM and SEM with or without PVP, indicating extensive agglomeration during preparation for microscopy. In contrast, without PVP stabilization, mean and mode sizes of respectively 35 ± 18 and 21 nm by spICPMS and 33 ± 15 and 20 nm by FI-spICPMS were obtained for suspensions of Ni NPs using external calibration with Ni standard solutions. With PVP stabilization, the mean and mode sizes respectively decreased to 27 ± 12 and 18 nm by spICPMS and 25 ± 10 and 16 nm by FI-spICPMS. Mass balance taking into account the amount of dissolved Ni was verified in all cases. No degradation in performance resulted from using FI-spICPMS instead of spICPMS, even though measurement of NPs mass by FI-spICPMS is done without knowledge of the transport efficiency and the sample uptake rate. This is the first time that spICPMS and FI-spICPMS are demonstrated to be suitable for the characterization of ferromagnetic NPs.

Ni Nanoparticle-Added Ni x /(Cu 0 . 5 Tl 0 . 5 )Ba2Ca2Cu3 O 10-δ Superconductor Composites and Their Enhanced Flux Pinning Characteristics

Ni nanoparticle-added Ni x /(Cu0.5Tl0.5)Ba2Ca2 Cu3 O 10-δ superconductor composites are synthesized at normal pressure by two-step solid-state reaction method. The idea for adding ferromagnetic nanoparticles was to create artificial pinning centers at grain boundaries. The samples have shown orthorhombic crystal structure in which the cell parameters increase with an increase in the added concentration of Ni nanoparticles. This shows that due to the higher reactivity, Ni nanoparticles partially diffuse into the unit cell of (Cu0.5Tl0.5)Ba2Ca2Cu3 O 10-δ superconductors. This also indicates as an evidence of the occupancy of these nanoparticles at grain boundaries. A metallic variation of resistivity from room temperature down to the onset of superconductivity is a typical feature of these samples with T c (R = 0) varying between 92 and 94 K. The magnitude of diamagnetism is significantly enhanced in 7 and 10% nanoparticle-added samples. The enhanced magnetization of ferromagnetic nanoparticles at reduced temperature plays a vital role in reducing the diamagnetism of nanosuperconductor composites. The softening of apical oxygen modes of type Cu(1)–OA–Cu(2) has confirmed the diffusion of Ni nanoparticles into the unit cell of the final compound. The excess conductivity analyses of conductivity data have shown that the values of B c (0), B c1, and J c are enhanced with the addition of Ni nanoparticles in the final compound. Variation of superconducting properties was attributed to pair breaking due to spin scattering across these ferromagnetic Ni nanoparticles. This shows that added Ni nanoparticles act as efficient pinning centers, which is also confirmed by the suppression of the London penetration depth.

Ferromagnetic (Ni) nanoparticles–CuTl-1223 superconductor composites

(Ni)x/CuTl-1223 (x=0, 0.25, 0.75, and 1.0wt%) nanoparticles–superconductor composites were synthesized by the addition of ferromagnetic nickel (Ni) nanoparticles in appropriate ratio to Cu0.5Tl0.5Ba2Ca2Cu3O10−δ (CuTl-1223) superconducting matrix. Structural, morphological, compositional and superconducting transport properties of these composites were studied by different experimental techniques. It was observed that the addition of Ni nanoparticles had not altered the crystal structure of host CuTl-1223 phase, which is somehow an evidence of the occupancy of these nanoparticles at the grain-boundaries. Suppression of superconducting properties was attributed to pair-breaking due to spin scattering across these ferromagnetic Ni nanoparticles. The enhanced magnetization of ferromagnetic Ni nanoparticles at reduced temperatures plays a significant role to reduce the diamagnetism of (Ni)x/CuTl-1223 composites. Fluctuation induced conductivity (FIC) analysis of resistivity versus temperature data has explained very well the effects of Ni nanoparticles on superconductivity of CuTl-1223 phase.

Flexible chains of ferromagnetic nanoparticles.

We report the fabrication of flexible chains of ferromagnetic Ni nanoparticles that possess the ability to adapt other than the typically observed rigid (nearly) straight configurations in the absence of an external magnetic field. The dynamic mobility of the ferromagnetic chains originates from a layer of densely grafted polyethylene glycol macromolecules enveloping each nanoparticle in the chain. While ferromagnetic chains of unmodified Ni nanoparticles behave as stiff nickel nanorods, the chains made of the grafted nanoparticles demonstrate extreme flexibility. Upon changing the direction of the field, and inevitably going through a zero-field point, the shorter chains undergo chain-globule-chain transformation. The longer chains can bend to a high degree, attaining "snake-like" configurations.

Residual DC voltage-free behaviour of liquid crystal system with nickel nanoparticle dispersion

In this study, we report on characterisation of residual DC voltage in homogeneously aligned nematic liquid crystal (N-LC) system with ferromagnetic Ni nanoparticles. A residual DC is greatly reduced in the N-LC cell as the increase of Ni particle concentration in LC mixture. The relationship between the doping concentration in Ni nanoparticles and the trapping of impurity ions was examined. In addition, the N-LC cells had faster response times and lower driving voltages, which translated to better electro-optical (EO) characteristics, than pure LC cells.

Phase, size and shape controlled formation of aerosol generated nickel and nickel oxide nanoparticles

• Structural and magnetic characterization of aerosol Ni nanoparticles. • Experimental parameters affecting size, shape and composition are discussed. • Larger spherical particles with the highest Ni content are produced by using an Ar flow. • Coalescence rate of primary particles is accelerated by increasing Ni feeding rate. • Ni nanoparticles show bulk-like saturation magnetization values. Ferromagnetic Ni nanoparticles were formed by a levitation-jet aerosol synthesis under different gas environments and metal precursor feed rates. At a constant background gas inlet temperature, it was found that a higher Ni loading resulted in enhanced particle growth through coalescence. He partial atmosphere favors surface condensation of evaporated Ni atoms over coalescence as the surface area reduction mechanism in the nanoparticles. A flow of 2.5% air in the background gas mixture was enough to oxidize 75% of the initial Ni load, inducing a drastic destabilization of particle size and shape distribution. Regardless of the background inert gas composition, necked nanoparticles were observed in samples prepared with a 1 g/h Ni feed rate, whereas discrete nanoparticles resulted from a higher feed rate of ca. 4 g/h, confirming the key role of Ni loading on the rate of coalescence. The highest saturation magnetization (51.75 A m 2 kg −1 measured at 300 K) and the lowest coercivity (0.008 T) were obtained under an Ar flow. Zero-field cooled and field-cooled magnetization curves measured under an applied field of 10 −2 T revealed that the blocking processes of nanoparticles are dominated by their particle size distributions, with some features attributable to interparticle interactions.

Nickel nanoparticles in carbon structures prepared by solid-phase pyrolysis of nickel-phthalocyanine

By using a modified method of solid-phase pyrolysis of metal-phthalocyanines, we have synthesized ferromagnetic Ni nanoparticles in different carbon structures: amorphous carbon plates, multiwall carbon nanotubes, carbon fibers, and graphitized capsules. The composition, structure and morphology of prepared composite materials have been studied by energy dispersive X-ray microanalysis, scanning and transmission electron microscopy, and X-ray diffraction technique. It has been found that the sizes of nickel nanoparticles (10–500 nm) and the type of carbon structures strongly depend on the pyrolysis conditions. By using the X-band ferromagnetic resonance measurements, we have revealed features of the temperature dependence of resonance spectra of single-domain and multi-domain Ni nanoparticles in Ni/C composites.

Fabrication of Ferromagnetic Ni(111) Nanoparticles Embedded Epitaxially in (Mg,Ni)O Matrix by Reduction of (Mg0.5Ni0.5)O(111) Epitaxial Thin Film

The ferromagnetic Ni nanoparticles could be epitaxially dispersed in the (Mg,Ni)O matrix by the oxide reduction. For this purpose, the epitaxial (Mg0.5Ni0.5)O thin film was grown at room temperature by pulsed laser deposition and successively reduced at 700 °C in hydrogen gas atmosphere. X-ray diffraction confirmed in-plane and out-of-plane epitaxial precipitation of Ni nanoparticles in the (Mg,Ni)O matrix by selective reduction of the Ni–O part in the epitaxial (Mg0.5Ni0.5)O thin film. Atomic-scale analyses indicated uniform dispersion of Ni nanoparticles (∼20 nm average size) in the (Mg,Ni)O matrix. Magnetic measurement confirmed ferromagnetic property of the Ni nanoparticle-containing (Mg,Ni)O thin films.

Preparation and characterization of nickel nanoparticles in different carbon matrices

Using the solid-phase pyrolysis and chemical vapor deposition of nickel-phthalocyanine, we have fabricated ferromagnetic Ni nanoparticles in carbon matrices. The composition, structure, morphology, and magnetic properties of samples were investigated by means of scanning electron microscopy, energy dispersive X-ray microanalysis, X-ray diffraction technique, and ferromagnetic resonance. It is shown that the sizes of nanoparticles can be varied from ∼10 nm to ∼500 nm depending on the temperature and time of pyrolysis. The used method allows us to synthesize metal nanoparticles in different carbon matrices: in amorphous carbon plates, in graphitic capsules, and in carbon nanotubes.

Porosity through reduction in metal oxides

AbstractRoutes to porous materials with nanoscale dimensions have been investigated. In the first example presented, porous manganese oxide has been prepared by leaching Ni metal from a nickel-manganese oxide precursor via reduction. Electron microscopy studies have revealed the presence of Ni nanoparticles on the surface, and also embedded within the porous MnO matrix. Magnetic measurements have shown exchange bias between the ferromagnetic Ni nanoparticles and the antiferromagnetic MnO phase. In the second system studied, porous nanostructures of rutile VO2 and corundum V2O3 have been prepared by reduction of amine-templated V2O5−δ nanoscrolls. The porosity of these materials has been probed by electron microscopy, N2 sorption measurements and thermogravimetric analysis.