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Superparamagnetic magnetite Fe3O4 nanoparticles (NPs) were synthesized by the coprecipitation method and stabilized with meso-2,3-dimercaptosuccinic acid (DMSA) under ambient conditions and a nitrogen atmosphere at room temperature in one simple step. The X-ray diffraction (XRD) analysis of Fe3O4 NPs confirmed their cubic spinel structure with high crystallinity for both samples prepared with or without nitrogen atmosphere. The scanning electron microscopy analysis showed an average particle size of 15.0 ± 3 nm and 23.0 ± 5 nm in the absence and presence of nitrogen, respectively. Our particles have shown excellent magnetic properties with a high saturation magnetization (55 emu/g), low remanence (3.0 emu/g), and low coercivity (43 Oe). The method of synthesis proposed here offers excellent reproducibility of superparamagnetic NPs with narrow size distribution and low aggregation despite the simplicity of its preparation. The dose–response curves of the colorimetric assay MTT carried out in HCT 116 cell cultures in a range from 30 to 250 μg/mL reveal that magnetic nanoparticles coated with DMSA significantly improve their biocompatibility for applications like magnetic hyperthermia, magnetic resonance imaging, or biosensing. [ABSTRACT FROM AUTHOR]

The angular dependence of the remanence and coercivity of Ni nanowire arrays produced inside the pores of anodic alumina membranes has been studied. By comparing our analytical calculations with our measurements, we conclude that the magnetization reversal in this array is driven by means of the nucleation and propagation of a transverse wall. A simple model based on an adapted Stoner–Wohlfarth model is used to explain the angular dependence of the coercivity. [ABSTRACT FROM AUTHOR]

The magnetostatic interaction between two ferromagnetic microwires is calculated as a function of their geometric parameters and compared with those measured through magnetic hysteresis loops of glass-coated amorphous Fe77.5Si7.5B15 microwires. The hysteresis loops are characterized by well-defined Barkhausen jumps corresponding each to the magnetization reversal of individual microwires, separated by horizontal plateaux. It is shown that the magnetostatic interaction between them is responsible for the appearance of these plateaux. Finally, using the expression for the magnetostatic interaction is trivial to obtain the interacting force between microwires. Our results are intended to provide guidelines for the use of these microwires with technological purpose such as the fabrication of magnetic sensors. [ABSTRACT FROM AUTHOR]

Properties of thin granular Co–SiO2 films have been studied by means of ferromagnetic resonance (FMR). The obtained FMR results are discussed using sample magnetization, electrical conductivity, and transmission electron microscopy analysis. Co and SiO2 were sequentially deposited for the sample preparation. The general behavior of the applied field for resonance could be described using effective out-of-plane anisotropies. A dipolar interaction model developed for magnetic heterostructures was applied to the interpretation of these anisotropies. The anisotropy terms caused by the magnetic particle shapes and by the film shape can explain the results for two metallic films close to percolation, in which the film shape is the preponderant contribution. In the case of an insulating sample, the consideration of an additional anisotropy term seems to be necessary to explain the results. [ABSTRACT FROM AUTHOR]

Granular T[M.sub.x][(Si[O.sub.2]).sub.1-x] (TM=Co, Fe, Ni) thin films are thermally treated at different temperatures and their magnetotransport and structural properties are analyzed. Results reveal that the changes in giant Hall effect upon annealing could depend on a particular combination of nanoparticle diameter, interparticle distance, and size distribution.

High quality single-crystalline hexagonal cobalt nanoplates have been obtained by a simple chemical reduction method using ultrasonic assistance. Individual nanoplates tend to form agglomerates due to their strong in-plane anisotropy. These particles were incorporated within a polyethylene matrix by a solution blending method and arrays of magnetic chains were generated by solidification of the solution of nanoparticles in the presence of a magnetic field. The easy axis of the Co plates is oriented along the field, in the direction of the chains length. Micromagnetic simulations, magnetic measurements, and FORC diagrams are used to clarify the complex magnetic behavior in these systems. [ABSTRACT FROM AUTHOR]

On-line measurements of resistance and temperature in melt-spun [Cu.sub.90] [Co.sub.10] ribbons are made using two different annealing techniques: conventional furnace annealing, and linearly varying current Joule heating. The aim of this paper is to consider the current, flowing through the sample during the annealing, as a possible parameter to control thermal treatment parameters and thus the microstructure of these systems. Although an exact way to obtain the temperature from the annealing current remains a difficult task, the on-line changes in resistance with current allows one to identify structural changes in the sample during annealing. Also, because the temperature is found to increase continuously with electrical current, it is possible to calibrate the Joule heating system to precisely determine the annealing temperature. Index Terms--Joule heating, binary alloys, nanocrystalline materials.

Arrays of Co and Ni nanowires of different lengths have been prepared by electrodeposition into nanopores of alumina membranes. The dependence of the coercivity of the arrays as a function of temperature and measurement angle of the nanowires has been measured. A simple model is presented in order to explain the behavior of the magnetic properties as a function of the angle of measurement. The analytical calculations show that while for Ni nanowires demagnetization reversal in the array is driven by means of the nucleation and propagation of a transverse wall, in Co arrays the reversal mode changes from curling to coherent when the angle of measurements changes. [ABSTRACT FROM AUTHOR]

Manganese oxides of spinel structure, LiMn2O4, Li1-xNixMn2O4 (0.25 ≤ x≤ 0.75), and NiMn2O4, were studied by EDS, XRD, SEM, magnetic (M-H, M-T), and XPS measurements. The samples were synthesized by an ultrasound-assisted sol-gel method. EDS analysis showed good agreement with the formulations of the oxides. XRD and Rietveld refinement of X-ray data indicate that all samples crystallize in the Fd3m space group characteristic of the cubic spinel structure. The a-cell parameter ranges from a = 8.2276 Å (x = 0) to a = 8.3980 Å (x = 1). SEM results showed particle agglomerates ranging in size from 2.3 μm (x = 0) down to 0.8 μm (x = 1). Hysteresis magnetization vs. applied field curves in the 5-300K range was recorded. ZFC-FC measurements indicate the presence of two magnetic paramagnetic-ferrimagnetic transitions. The experimental Curie constant was found to vary from 5 to 7.1 cm3 K mol−1 for the range of compositions studied (0 ≤ x ≤ 1). XPS studies of these oxides revealed the presence of Ni2+, Mn3+, and Mn4+. The experimental Ni/Mn atomic ratios obtained by XPS were in good agreement with the nominal values. A linear relationship of the average oxidation state of Mn with Ni content was observed. The oxide’s cation distributions as a function of Ni content from x = 0  Li+[Mn3+Mn4+]O4 to x = 1 Ni0.352+Mn0.653+Ni0.652+Mn1.353+O4 were proposed. [ABSTRACT FROM AUTHOR]

Granular TMx(SiO2)1-x (TM=Co,Fe,Ni) thin films were thermally treated at different temperatures and their magnetotransport and structural properties were studied. Hall resistivity decreases with thermal annealing. Structure was analyzed based on small angle x-ray scattering results. A model of polydisperse system of hard spheres was used for obtaining structural parameters. Analysis reveals that a volume fraction of transition-metal atoms (less than 29%) are forming nanospheres. Changes in giant Hall effect upon annealing can depend on a particular combination of nanoparticle diameter, interparticle distance, and size distribution. [ABSTRACT FROM AUTHOR]

In this work, Barkhausen noise measurements are shown for a series of amorphous ribbons: Metglas 2605TCA, Metglas 2705M, and Finemet materials with composition Fe[sub 73.5]Cu[sub 1]Nb[sub 3]Si[sub 18.5]B[sub 4] under different stress (σ) and annealing temperature (T[sub A]) conditions. The dynamical state of the system is characterized by the power spectra and amplitude distribution functions as well as by the Minkowski-Bouligand dimension for each set of samples. Special attention has been paid to the ranges of vanishing anisotropies: low applied stress for the Metglas samples and the nanocrystallized phase of Finemet materials. [ABSTRACT FROM AUTHOR]

Homogeneous nickel nanoparticles were synthesized and supported over m-ZrO2 through a simple ultrasonic process. The microscopic and magnetic characterization of nanoparticles showed high quality and effective monodisperse size distribution. The catalytic performance of the samples, containing only 1% wt nickel, was evaluated for CO2 methanation reaction. The experimental results showed high activity (70%) and excellent selectivity to CH4 (90% at 720 K). This low-cost and simple fabrication method of a nanocatalyst proves to be a potential candidate for further application. [ABSTRACT FROM AUTHOR]