D.H. Manh

Magnetic fluid based on Fe3O4 nanoparticles: Preparation and hyperthermia application

The paper presents results of research on preparing the magnetic fluid based on Fe3O4 nanoparticles and its potential hyperthermia application. Magnetic fluids were manufactured by dissolving superparamagnetic nanoparticles coated by suitable biocompatible starch layer during the co-precipitation processing. The coated particle size changes in range of 15÷17 nm were characterized by FESEM images. At room temperature, the samples exhibit super-paramagnetic behaviour with a saturation moment of 65 emu/g. The concentration of magnetic nanoparticles contained in carried liquid reach to 15 mg/ml. The magnetic fluid was used as a mediator for heating by an AC magnetic field with the frequency of 184 kHz and field strength of 12 kA/m. The dependence of heating on nanoparticle concentration was observed and it implied that the magnetic fluid is a suitable mediator for cancer treatment by hyperthermia application with appropriate controlling the heating temperature ranges from 45 to 50°C.

Magnetic nanoparticles: study of magnetic heating and adsorption/desorption for biomedical and environmental applications

This paper presents a summary of research on magnetic nanoparticles (MNPs) carried out recently at the Institute of Materials Science. Three families of oxide MNPs namely magnetite, manganite and spinel ferrite materials were prepared by several methods: co-precipitation, sol-gel and high-energy mechanical milling. Magnetite nanoparticles were encapsulated by two natural polymers, starch and chitosan. The structure of the prepared nanosystems was characterised by XRD, SEM, TEM techniques while their magnetisation was measured by VSM and PPMS. The magnetic heating (MH) of both naked and polymer-coated MNPs was studied. We also present two examples of researched applications that can be derived from this effect, namely the use of MH of magnetite NPs coated with starch to kill cancer cells, and the MH-assisted desorption of VOC from SBA/ferrite nanocomposite. Other research application examples include the use of magnetite MNPs to remove heavy toxic metals, such as arsenic, lead and nickel from contaminated water.

Perovskite nanoparticles synthesised by reactive milling combined with thermal processing: preparation, morphology and structure characterisation

Reactive milling and thermal processing methods were used to prepare a large variety of perovskites like ABO3 and La2NiO4. The single-phase nanoparticle of ABO3 was synthesised at different milling times in dependence on the starting oxides. The grain size of ABO3 nanoparticles in the range of 10-30 nm was conditional upon milling time. Single-phase nanoparticles of La2NiO4 were obtained by using 6 h milling combined with annealing at 750°C. A structure conversion from a layer into a single perovskite of La2NiO4 was observed as milling time increased, whereas the crystalline structure of ABO3 remained almost unchanged. Further analysis of HRTEM images confirms a core-shell structure of nanoparticles.

Microwave Absorption in

La_1.5Sr_0.5NiO₄ is well known as a dielectric material that has a colossal permittivity (up to 10⁷) and a weak paramagnet at room temperature. The permeability is about 1.005, which is just slightly larger than that of air. The weak magnetic moment together with the huge imbalance between permittivity and permeability seemed to negate La_1.5Sr_0.5NiO₄ as a promising candidate for electromagnetic absorption due to the lack of magnetic losses. However, we have found that La_1.5Sr_0.5NiO₄ nanopowder indeed has a reasonably strong microwave absorption capability in the range of 4-18 GHz. Apparently, impedance matching (|Z| = Z₀ = 377 Ω) is found to be responsible for the absorption resonance that shifts to lower frequencies with increasing the absorbers thickness. To improve magnetic losses, as well as to balance out the dielectric and magnetic components, CoFe₂O₄ nanoparticles are gradually added to the La_1.5Sr_0.5NiO₄/CoFe₂O₄ composites. The influence of adding magnetic nanoparticles on reflection loss, resonance frequency, and matching effects will be discussed.

{\rm La}_{1.5}{\rm Sr}_{0.5}{\rm NiO}_{4}/{\rm CoFe}_{2}{\rm O}_{4}

Fe65Co35 nanoparticles were prepared by mechanical alloying of the elemental Fe and Co powders in air. The structural, morphology, and magnetic property variations were investigated as a function of milling time (in the 0.25–32 h range) by using xray diffraction, scanning electron microscopy, and vibrating sample magnetometry. The complete formation of bcc Fe65Co35 solid solution was observed after 10 h milling. At this time, the alloy powder with average grain size (crystallite size) of 12 nm and a maximum saturation magnetization (Ms) 200 emu/g was obtained. Intensive milling of Fe-Co powders resulted in a grain refinement down below 10 nm and in reduction of Ms to 170 emu/g. The saturation magnetization of the alloys asmilled for various milling times was almost unchanged, at least after seven days of storing in air, which suggests a formation of certain oxide layer on particles surface to protect them from further oxidation. The annealing of as-milled sample at 800C under gas mixture of hydrogen and argon affected in a strong increase of Ms, from 170 emu/g to 220 emu/g, that supports the above hypothesis on the existence of the oxide layer.

Nanocomposites (Revised Feb. 2014)

In this study, we report the electric transport of La0.7Ca0.3MnO3 prepared by various methods. Based on the fact that the metallic ferromagnetic and insulating paramagnetic clusters simultaneously exist at transition temperature, we applied phase-coexistence transport model to calculate the temperature dependence of the resistivity. This model can explain quantitatively the electrical conductivity of La0.7Ca0.3MnO3 for the whole temperature range studied.

Facile Synthesis of High Magnetization Air-stable Fe65Co35 Nanoparticles by Mechanical Alloying

Magnetization and transport of (1 – x)La0.7Ca0.3MnO3 +xAg (x = 0, 0.1, 0.2, 0.3, 0.4 and 0.5) composites has been reported in this paper. Low Field Magnetoresistance (LFMR), conductivity (σ) and metal – insulator transition temperature (Tp) increases with increasing content of Ag. Due to the presence of nomagnetic Ag in the ferromagnetic La0.7Ca0.3MnO3 material, dc magnetization decreases but the corresponding Tp increases. Based on the spin polarized transport of conduction electrons at the grains boundaries, we find that our experimental data (MR – H) agree quite well with the dependence of temperature on tunneling magnetoresistance (TMR) described by an expression of Hwang et al.

Electrical transport study of La0.7Ca0.3MnO3 using phase - coexistence transport model

Colloidal CdSe tetrapods were synthesized by chemical method in octadecene with the initial Cd:Se precursor ratios from 6:1 to 1:10 and the different monomer concentrations. Their stoichiometry and optical properties were investigated using the energy dispersion X-ray, absorption and photoluminescence spectroscopy. It was found that the CdSe tetrapods are Cd rich for all of the obtained sizes. Their stoichiometry was almost not changed during the growth and depends on the initial precursor ratio. The double-peak structure corresponding to the optical transitions in the core and arms of CdSe tetrapods was observed clearly in both the optical absorption and photoluminescence spectra for the Cd:Se precursor ratios from 2:1 to 1:2. The influence of the initial Cd:Se precursor ratio and monomer concentration on the growth of CdSe tetrapods and their optical properties has been analysed and discussed.

Tunnelling mafnetoresistance of (1 – x)La0.7Ca0.3MnO3 +xAg composites

In this paper, we report the effect of Pb doping on the magnetic and magnetocaloric properties of La0.7Ca0.3-xPbxMnO3 (0.15 ≤ x ≤ 0.3) polycrystalline samples. The samples were prepared by solid state synthesis method. X-ray diffraction patterns indicate that these samples have monoclinic structure with the Pc/2 space group. The magnetization measurements indicated that all samples exhibited a paramagnetic–ferromagnetic transition and the transition temperature increased with increasing of Pb concentration. Using phenomenological model, the magnetocaloric behavior of all the samples has been calculated based on the experimental magnetization data. Our results on the magnetocaloric properties suggest that the compound La0.7Ca0.15Pb0.15MnO3 is attractive as a possible material for magnetic refrigeration.

Influence of Cd:Se precursor ratio on optical properties of colloidal CdSe tetrapods prepared in octadecene

In this report we present our recent results on fabrication of Nd-Fe-B exchange-spring magnets using melt-spinning method. Additive elements were used to improve useful parameters of this kind of hard magnetic materials. Hot pressing technique was applied to increase mass density of the magnets. The compositions and technology routes for fabricating the Nd-Fe-B exchange-spring magnets with maximum energy product (BH)max above 10 MGOe were shown.