Le Van Hong

Structural, optical and magnetic properties of polycrystalline BaTi1−xFexO3 ceramics

Polycrystalline BaTi1−xFexO3 ceramics have been prepared by conventional solid-state reaction. Their structural, optical and magnetic properties are then studied by means of x-ray diffraction (XRD), Raman scattering (RS) and absorption spectrometers, and a physical properties measurement system. Detailed analyses of XRD patterns and RS spectra reveal the phase separation of the tetragonal-hexagonal structure at a threshold concentration of x = 0.005. The increase in the Fe-doping content (x) leads to development of the hexagonal phase. Magnetic measurements prove that many BaTi1−xFexO3 samples exhibit the room-temperature ferromagnetic order, excepting the samples with x = 0.02–0.06. The ferromagnetism depends strongly on concentration of Fe impurities. The nature of this ferromagnetism is discussed by means of the results of structural analyses and optical absorption spectra.

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.

Structural phase separation and optical and magnetic properties of BaTi1−xMnxO3 multiferroics

Our work studies the influences of the Mn doping on structural characterization and optical and magnetic properties of BaTi1−xMnxO3 (x = 0.0–0.12) prepared by conventional solid-state reaction. Detailed analyses of XRD patterns and Raman scattering spectra indicate an incorporation of Mn dopants into the Ti sites of BaTiO3 host lattices, and the tetragonal-hexagonal transformation taking place at a threshold concentration of xc ≈ 0.01. An increase of Mn-doping content in BaTi1-xMnxO3 introduces more electronic levels associated with lattice defects and Mn ions to the forbidden gap and thus reduces luminescent intensity in the visible region. Magnetic data recorded at room temperature reveal that all the samples exhibit ferromagnetic order, and there is a phase separation in magnetism as varying x values. Particularly, the samples with x = 0.5–0.7 have a coexistence of two ferromagnetic phases with different coercivities, which are associated with tetragonal and hexagonal Mn-doped BaTiO3 structures. The na...

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.

Structure and high photocatalytic activity of (N, Ta)-doped TiO2 nanoparticles

A hydrothermal method was used to prepare three nano-crystalline samples of TiO2 (S1), N-doped TiO2 (S2), and (N, Ta)-codoped TiO2 (S3) with average crystallite sizes (D) of 13–25 nm. X-ray diffraction studies confirmed a single phase of the samples with a tetragonal/anatase structure. A slight increase in the lattice parameters was observed when N and/or Ta dopants were doped into the TiO2 host lattice. Detailed analyses of extended X-ray absorption spectra indicated that N- and/or Ta-doping into TiO2 nanoparticles influenced the co-ordination number and radial distance (R) of Ti ions in the anatase structure. Concerning their absorption spectra, (N, Ta)-doping narrowed the band gap (Eg) of TiO2 from 3.03 eV for S1 through 2.94 eV for S2 to 2.85 eV for S3. Such results revealed the applicability of these nanoparticles in the photocatalytic field working in the ultraviolet (UV)-visible region. Among these, photocatalytic activity of S3 was the strongest. By using S3 as a catalyst powder, the degradation e...

Magnetoresistance and magnetocaloric properties of La0.7Sr0.3Co0.95Mn0.05O3 compound

The magnetoresistance and magnetocaloric effects were studied via magnetic and electric properties measurements. The ferromagnetic transition temperature and critical exponents, which are determined by analyzing the Arott plots, to be TC = 190.665K, ? = 0.456, ? = 1.0623 and ? = 3.2845, respectively. Although ferro-paramagnetic transition was observed clearly with TC of 190 K but the insulating behaviour is remained in a whole in a temperature region of 5 K up to 300 K. Moreover the negative magnetoresistance shows a shoulder at ~TC, broadens toward lower temperature and reach maximum of 11.5% at 174 K in applied field of 5 T. This result is explained as due to the competing between ferromagnetic and non-ferromagnetic phases in the sample. The magnetization measurements were performed in a narrow temperature range, close to TC and external magnetic fields up to 4.5T. The adiabatic magnetic entropy changes, ?S, determined from magnetization data, shows a maximum at TC.

Sol–Gel Synthesis, Characterization, and Magnetic Properties of Double-Layered Perovskite Manganite La 1.25 Sr 1.75 Mn 2 O 7

Bilayered perovskite manganites of the composition La1.25Sr1.75Mn2O7 (LSMO) were synthesized successfully by the sol-gel method. The effects of pH concentration, calcination temperature, and time on the phase formation, structure, and magnetic properties of the material were systematically investigated. X-ray diffraction and Rietveld refinement analysis revealed that the single phase of LSMO was only obtained in samples sintered at a temperature as high as 1250°C. The best magnetic properties were achieved in samples with pH = 7, calcinated at 1450°C for 10 h. Our studies show that the pH concentration, calcination temperature, and time are important factors in tailoring the magnetic properties of double-layered perovskite manganites.

Magnetic Properties of Annealed Powders Prepared By Mechanical Alloying

Fe-Co alloy powders were prepared by mechanical alloying of the elemental Fe and Co powders in air and subsequently annealed at various temperatures. Structural and magnetic characteristics of the annealed powders were studied in detail as a function of annealing temperatures by using an X-ray diffractometer (XRD), a field emission scanning electron microscope, a vibrating sample magnetometer, and a physical property measurement system. The XRD results showed an existence of the nanocrystals with sizes of 15-50 nm. The magnetic studies indicated a strong increase of magnetization and a sharp decrease of coercivity as annealing temperature increased. Both the effect of the oxidation on the magnetic properties as well as magnetization stability of the annealed samples will be discussed.

Superparamagnetic behaviour and deviation from Bloch T3/2 law of La0.7Ca0.3MnO3 nanoparticles

In this study, we investigated superparamagnetism behaviour and saturation magnetisation of single–phase, nanocrystalline, granular La0.7Ca0.3MnO3 (LCMO) samples synthesised by reactive milling method. The superparamagnetic behaviour of as–milled samples with various milling times was studied in the temperature range from 200 K to 300 K. The saturation magnetisation of the samples increased from 14.7 to 36.8 emu/g with higher values corresponding to shorter milling time. The observed un–overlapping of the scaled M(Hext, T)/MS versus Hext/T plots and the Curie–Weiss like behaviour of the dc–susceptibility at high temperatures provide evidence that the nanoparticles are interacting superparamagnetic ensembles. The magnetisation curves of interacting nanoparticles were well described by the argument–corrected Langevin function. The saturation magnetisation versus temperature showed a Te dependence with e deviated from 3/2 (value for the Bloch law), which increased with decreasing of the milling time.