Nguyen Hoang Luong

Crystallization process and magnetic properties of amorphous iron oxide nanoparticles

This paper studied the crystallization process, phase transition and magnetic properties of amorphous iron oxide nanoparticles prepared by the microwave heating technique. Thermal analysis and magnetodynamics studies revealed many interesting aspects of the amorphous iron oxide nanoparticles. The as-prepared sample was amorphous. Crystallization of the maghemite ?-Fe2O3 (with an activation energy of 0.71?eV) and the hematite ?-Fe2O3 (with an activation energy of 0.97?eV) phase occurred at around 300??C and 350??C, respectively. A transition from the maghemite to the hematite occurred at 500??C with an activation energy of 1.32?eV. A study of the temperature dependence of magnetization supported the crystallization and the phase transformation. Raman shift at 660?cm?1 and absorption band in the infrared spectra at 690?cm?1 showed the presence of disorder in the hematite phase on the nanoscale which is supposed to be the origin of the ferromagnetic behaviour of that antiferromagnetic phase.

Preparation and properties of silver nanoparticles loaded in activated carbon for biological and environmental applications

Silver nanoparticles colloid has been prepared by a modified sonoelectrodeposition technique in which a silver plate was used as the source of silver ions. This technique allows producing Ag nanoparticles with the size of 4-30 nm dispersed in a non-toxic solution. The Ag nanoparticles were loaded in a high surface activated carbon produced from coconut husk, a popular agricultural waste in Vietnam by thermal activation. The surface area of the best activated carbon is 890 m(2)/g. The presence of Ag nanoparticles does not change significantly properties of the activated carbon in terms of morphology and methylene blue adsorption ability. The Ag nanoparticle-loaded activated carbon shows a good antibacterial activity against Escherichia coli with very low minimal inhibitory concentration of 16 μg/ml and strong As(V) adsorption. The materials are potential for prevention and treatment of microbial infection and contamination for environmental applications.

On the magnetic and magnetocaloric properties of perovskite La1−xSrxCoO3

Abstract Structural, magnetic and magnetocaloric studies on La 1− x Sr x CoO 3 (0.20⩽ x ⩽0.50) were reported. The crystal structure of the samples is rhombohedral with x =0.20–0.45 and is cubic with x =0.50. Magnetization, Curie temperature ( T c ) and maximum magnetic-entropy change (Δ S max ) depending on the Sr content in the samples are discussed. La 0.55 Sr 0.45 CoO 3 exhibits the largest value for Δ S max and T c among the compounds investigated.

Magnetic properties of FePt nanoparticles prepared by sonoelectrodeposition

Sonoelectrodeposition is a useful technique to make metallic nanoparticles, using ultrasound during electrodeposition to remove nanoparticles as they grow on the cathode surface. This paper reports some structural and magnetic properties of FePt nanoparticles prepared by this method. The as-prepared Fe45Pt55 nanoparticles were ferromagnetic at room temperature. Upon annealing at 700°C for 1 h under H2 atmosphere, the saturation magnetization and the coercivity of the nanoparticles were improved significantly. The annealed nanoparticles showed a high coercivity of 13.5 kOe at 2 K and of 9 kOe at room temperature. Sonoelectrodeposition is a promising technique to make large quantity of FePt nanoparticles.

Preparation of magnetic nanoparticles embedded in polystyrene microspheres

Superparamagnetic particles are widely used for biological applications such as cell separation. The size of the particles is normally in the range of 10 – 20 nm which is much smaller than the size of a cell. Therefore small particles create small force which is not strong enough to separate the cells from solution. Superparamagnetic nanoparticles embedded in Polystyrene microspheres (magnetic beads) are very useful for cell separation. Magnetic beads have been prepared by solvent evaporation of an emulsion. The beads with size of 0.2 μm – 1.0 μm have a saturation magnetization of 10 – 25 emu/g. The change of the amount of surfactants, volatile solvent, magnetic particles resulted to the change of size, magnetic properties of the magnetic beads.

Arsenic removal from water by magnetic Fe1− x Co x Fe2O4 and Fe1− y Ni y Fe2O4 nanoparticles

This article studies the effects of Co and Ni replacement in Fe1− x Co x Fe2O4 and Fe1− y Ni y Fe2O4 (x, y = 0, 0.05, 0.1, 0.2, 0.5) nanoparticles, pH, weight of nanoparticles/mL of water, and time of stirring on the arsenic removal ability. The results showed that a small amount (0.25 g L−1) of Fe3O4 nanoparticles after stirring time of 3 min can reduce the arsenic concentration from 0.1 to 0.01 mg L−1. The removal was also affected by the pH of the water. Absorption of arsenic by nanoparticles was effective when pH was smaller than seven and reduced with the increase of pH. At pH of 13, there was a strong release of arsenic ions from arsenic-absorbed nanoparticles back to water. The time of stirring was studied from 1 min to 2 h and the optimal time was about few minutes. Co and Nis presence was reported to keep saturation magnetisation stable under working conditions. For Co replacement, absorption does not change significantly when x ≤ 0.1 and slightly reduces when x > 0.1. The presence of Ni improved the absorption in most cases.

Co–Pt nanoparticles encapsulated in carbon cages prepared by sonoelectrodeposition

Co-Pt nanoparticles encapsulated in carbon cages have been prepared by sonoelectrodeposition followed by annealing in a CO atmosphere. Sonoelectrodeposition is a useful technique to make metallic nanoparticles, using ultrasound during electrodeposition to remove nanoparticles as they grow on the cathode surface. We used an electrolyte containing chloroplatinic acid and cobalt chloride and found that the atomic ratio of Co:Pt in the as-formed materials varied from 0.2 to 0.8 as the deposition current density was changed from 15 to 35 mA cm(-2). However, the as-deposited materials were inhomogeneous, comprising a mixture of Pt-rich and Co-rich nanoparticles. X-ray diffraction indicated that subsequent heat treatment (700 °C for 1 h) under CO gas created an ordered CoPt alloy phase that exhibited hard magnetic properties. Transmission electron microscopy showed many of the resulting nanoparticles to be encapsulated in carbon cages, which we ascribe to Co-catalyzed decomposition of CO during annealing. The thickness of the carbon cages was about ten layers, which may have helped reduce sintering during annealing. The size of the resultant nanoparticles was about 100 nm diameter, larger than the typical 5-10 nm diameter of as-deposited nanoparticles.

The influence of Tantalum content in relation to substrate temperature on magnetic and structural properties of Co-Cr-Ta thin films

In this study, we investigated the influence of Ta content (in Co86Cr12Ta2 and Co82Cr13Ta5 compositions) on magnetic and structural properties of Co–Cr–Ta perpendicular media samples grown on Si substrates at different substrate temperatures during RF-sputter deposition. In general, coercivity of Co82Cr13Ta5 samples is higher than that of Co86Cr12Ta2 samples, whereas the perpendicular c-axis orientation of Co86Cr12Ta2 samples is better. Ta content was suggested to be in between 2 and 5 at% to give optimum magnetic and structural properties.

Influence of B content substituting for Al on the magnetic properties of Nd60Fe30Al10−xBx

Abstract The Nd 60 Fe 30 Al 10− x B x ( x =0, 2, 4, 6, 8 and 10) alloys were prepared by copper mold casting using arc-melting. Investigation shows that with increasing B content magnetization and remanence decrease while coercivity and Curie temperature increase. The hard magnetic properties are achieved not only in the amorphous state but also in partly crystallizing state.

Influence of La doping on the properties of SrBa hexagonal ferrites

Abstract A series of SrBa ferrites with composition (Sr0.75Ba0.25)1−x(La2O3)x/2·5.3Fe2O3 has been prepared by the conventional ceramic technology. The size of the crystallites corresponds to that of a single magnetic domain. Doping of La not only enhances the coercivity of these materials but also improves the remanence. The reasons for improving the hard magnetic properties of the investigated ferrites are discussed.