Iron-nickel Nanoparticles Research Articles

CTAB-mediated synthesis of iron–nickel alloy nanochains and their magnetic properties

One-dimensional nanochains consisting of crystalline iron–nickel nanoparticles were successfully synthesized by a simple cetyltrimethylammonium bromide (CTAB) mediated assembly method. The structure and magnetic properties of the nanochains were investigated. The product is composed of nanochains with a diameter of about 90–110nm and length about several micrometers. A possible formation mechanism of these 1D particle assemblies was proposed. It was found that CTAB can serve as an effective cross-linker and plays an important role in the formation of nanochains. CTAB with low concentration can adsorb on the surface of particles and partially compensate the negative surface charge, leading to an anisotropic distribution of the residual surface charges. And this extrinsic electric dipole formation is responsible for the linear organization of the particles into chains. As-prepared iron–nickel nanochains exhibit ferromagnetism at room temperature with a much enhanced magnetic coercivity over three orders of magnitude larger than that of bulk permalloy. The imaginary part μ″ of the permeability for FeNi3-chain/wax composite shows a broad resonance peak in the frequency range 150MHz to 4GHz. Meanwhile, the position and width of resonance peak can be tuned via magnetic-field orientation treatment.

Characterization of magnetic nanoparticles by a modular Hall magnetometer

The magnetization of iron oxide, nickel and cobalt ferrite nanoparticles was successfully measured by using a modular magnetometer. The magnetometer was built by combining stand-alone equipments usually available at most laboratories such as a Gaussmeter, an electromagnet, a current source and a linear actuator. The magnetic moment sensitivity attained was about 10 −6 Am 2 and the results were checked against measurements made on commercial VSM and SQUID magnetometers showing few percent errors.

The effects of vacuum annealing on the structure and surface chemistry of iron:nickel alloy nanoparticles

In order to increase the longevity of contaminant retention on the particle surface, a method is sought to improve the corrosion resistance of bimetallic iron nickel nanoparticles (INNP) used for the remediation of contaminated water, and thereby extend their industrial lifetime. A multi-disciplinary approach was used to investigate changes induced by vacuum annealing (<5 × 10−8 mbar) at 500 °C on the bulk and surface chemistry of INNP. The particle size was determined to increase significantly as a result of annealing and the thickness of the surface oxide increased by 50%. BET analysis recorded a decrease in INP surface area from 44.88 to 8.08 m2 g−1, consistent with observations from scanning electron microscopy (SEM) and transmission electron microscopy (TEM) which indicated the diffusion bonding of previously discrete particles at points of contact. X-ray diffraction (XRD) confirmed that recrystallisation of the metallic cores had occurred, converting a significant fraction of initially amorphous iron nickel alloy into crystalline FeNi alloy. X-ray photoelectron spectroscopy (XPS) indicated a reduction in the proportion of surface iron oxide and a change in its stoichiometry related to annealing-induced disproportionation. This was also evidenced by an increased proportion of Fe(0) and Ni(0) to Fe- and Ni-oxides, respectively. The data also indicated the concurrent development of boron oxide at the metal surfaces, which accounts for the overall increase measured in surface oxide thickness. The improved core crystallinity and the presence of passivating impurity phases at the INNP surfaces may act to improve the corrosion resistance and reactive lifespan of the vacuum annealed INNP for environmental applications.

Synthesis of iron–nickel nanoparticles via a nonaqueous organometallic route

Fe–Ni nanoparticles have been synthesized via a nonaqueous solution-phase approach using thermal decomposition of Ni(II) acetylacetonate and Fe(III) acetylacetonate in oleylamine without further reducing agents. The analyses of powder X-ray diffraction and transmission electron microscopy show that the as-synthesized Fe–Ni nanoparticles possess a face-centered cubic (fcc) crystalline structure and exhibit a polydispersed characteristic. The particle morphology and size distribution can be further controlled by introducing surfactants in the reaction system, and the final chemical composition also can be tuned to some extent by varying the initial molar ratios of metal precursors. Room temperature magnetic measurements reveal a ferromagnetic characteristic for the as-synthesized nanoparticles. An increased saturation magnetization has been observed with increasing Fe contents.

Nanoscale analysis of three-dimensional structures by electron tomography

A significant challenge to the design of nanoscale materials and devices is the difficulty of characterising complex three-dimensional structures on small length scales. Electron tomography, a technique pioneered in the life sciences, has been developed for materials science by using high-angle annular dark-field scanning transmission electron microscopic tomography and energy filtered transmission electron microscopic tomography. We present tomographic analyses that reveal three very different types of information: the crystal habit of magnetite in magnetotactic bacteria, the morphology and composition of a silicon–germanium quantum dot, and compositional variations in iron–nickel nanoparticles. Both techniques are shown to return chemical and structural information that would be unattainable using conventional two-dimensional microscopy.

Modeling Structural and Magnetic Phase Transitions in Iron-Nickel Nanoparticles

Martensitic phase transformations and magnetovolume effects in iron-nickel alloys are intimately related. The term Invar is widely used to characterize the unusual physical properties accompanying structural and magnetic instabilities such as those observed in the vicinity of the critical composition Fe 65 Ni 35 . We discuss the crossover from bulk iron-nickel alloys to nanoparticles with respect to structural and magnetic behavior. By employing molecular-dynamics and Monte Carlo methods, we find the absence of structural instabilities in defect-free particles, a linear scaling of the austenitic transformation temperature with the reciprocal cluster radius, as well as a decrease of the magnetic transition temperature with decreasing particle size.