ABSTRACT
Nd2Fe14B is one of the most popular permanent magnets (PMs) possessing the best energy product (BH)max among the common PM materials. However, exchange-coupled nanocomposite magnets fabricated by embedding nanostructures of soft-phase magnetic materials into a hard-phase magnetic matrix manifest higher remanence and a higher energy product. Here we present the fabrication of exchange coupled Nd2Fe14B/Fe-Co magnetic nanocomposites using gel-combustion and diffusion-reduction processes. Pre-fabricated CoFe2O4 nanoparticles (NPs) of â¼5 nm diameter were incorporated into a Nd-Fe-B oxide matrix during its synthesis by gel-combustion. The obtained mixed oxide was further processed with oxidative annealing at 800 °C for 2 h and reductive annealing at 900 °C for 2 h to form a Nd2Fe14B/Fe-Co nanocomposite. Nanocomposites with different mol% of soft-phase were prepared and characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM) and physical property measurement system (PPMS) to study their crystalline phase, morphology and magnetic behavior. Addition of 7.7 mol% of soft-phase was found to be optimum, producing a coercivity (H c) of 5.6 kOe and remanence (M r) of 54 emu g-1 in the nanocomposite.
ABSTRACT
The effect of 60Co gamma-ray irradiation on the microstructure of Nd2Fe14B magnets was investigated with electron spin resonance (ESR) and thermal mechanical analyzer (TMA). When the 60Co gamma-ray with dose from 0 Mrad to 100 Mrad was exposed to Nd2Fel,4B magnet having different sizes at room temperature, the increased demagnetization properties of the Nd2Fe14B magnets were studied by Hall probe. For all samples, changed Curie temperature and micro-crystal structure of Nd2Fe14B magnet by gamma-ray irradiation has been also studied. Moreover the strong and broad single line shaped ESR signal in the resonance magnetic field is attributed to unpaired electron of iron ions in the sample by the effect of gamma-ray irradiation.
ABSTRACT
Co(30)Fe(70) nanoparticles with mean particle size of about 8 nm were successfully synthesized by the chemical reduction of cobalt chloride and iron chloride with borohydride as a reducing agent in aqueous solution. The composition and size of the Co(30)Fe(70) nanoparticles were optimized by controlling the molar ratio of starting materials, reaction time, and dropping rate of aqueous reducing agent. As alloy powders prepared by chemical reduction tend to be amorphous in the as-synthesized state, the as-precipitated Co(30)Fe(70) nanoparticles were heat-treated to achieve crystallinity at the different temperatures for 1 h. The Co(30)Fe(70) nanocrystallite by chemical reduction shows excellent soft magnetic behavior, such as high permeability, negligible coercivity, and high saturation magnetization like that of Co(30)Fe(70) bulk.
ABSTRACT
A new preparation for highly crystalline and monodisperse Fe3O4 nanoparticle is reported. This synthesis requires the use of rather complicated procedures including delicate control of surfactants ratios and inert reaction conditions due to the toxic and unstable nature of the precursors none the less because thermal decomposition methods were tried to synthesize monodispersed inorganic nanocrystallites until very recently. The synthesis of Fe3O4 nanocrystallites by using Fe(+2)-oleate2 complex was studied. The Fe(+2)-oleate2 complex was prepared from the reaction of iron chloride and sodium oleate in water. The thermal decomposition of the complex at the reduced pressure (0.3 torr) and about 300 degrees was done without any solvent. We demonstrated that a new solventless synthesis of size- and shape-monodisperse Fe3O4 nanoparticles depends on the amount of Na-oleate. And it is possible to remove the oleate ligand using reduction process. We confirmed that the nanoparticles changed from Fe3O4 to alpha-Fe phase obtained higher magnetic properties and crystallites by a vibrating sample magnetometer (VSM) and x-ray powder diffraction (XRD). Removal of the organic surfactant and other volatile components surrounding Fe3O4 nanoparticles was detected by fourier transform infrared spectroscopy (FT-IR).
