T. Koutzarova

Structural and Magnetic Properties of Nanosized Barium Hexaferrite Powders Obtained by Microemulsion Technique

Thin hexagonal barium hexaferrite particles synthesized using the microemulsion technique were studied. A water-in-oil reverse microemulsion system with cetyltrimethylammonium bromide (CTAB) as a cationic surfactant, n-butanol as a co-surfactant, n-hexanol as a continuous oil phase, and an aqueous phase were used. The microstructural and magnetic properties were investigated. The particles obtained were mono-domain with average particle size 280 nm. The magnetic properties of the powder were investigated at 4.2 K and at room temperature. The saturation magnetization was 48.86 emu/g and the coercivity, 2.4 x 105 A/m at room temperature. The anisotropy field Ha and magneto-crystalline anisotropy K1 were 1.4 x 106 A/m and 2.37 x 105 J/m3, respectively.

The Influence of the Polycrystalline State and Partial Dy Substitution on the Superconducting Properties of YBCO

The influence of the quasi-equal partial substitution of non-magnetic (Y 3+ )/magnetic (Dy 3+ ) ions in YBa 2 Cu 3 O 7-y on the superconducting properties of the material has been investigated. To minimize the influence of the stress field induced by lattice mismatch, Dy-substituted YBa 2 Cu 3 O 7-y was studied because Y 3+ and Dy 3+ ions have similar ionic radii. The investigation was performed on polycrystalline and powder samples with general formula Dy x Y 1-x Ba 2 Cu 3 O 7-y (x = 0.4-0.6). Higher magnetic losses and intragranular critical current density J c were observed for partially substituted samples in comparison with DyBCO. The strongest influence of magnetic substitution on the electrical resistivity properties was observed in the mixed state.

Magnetic properties of nanosized MgFe2O4 powders prepared by auto-combustion

Targets were prepared to be used for magnetron sputtering and laser ablation and their microstructural and magnetic properties were investigated. The base material was nanosized MgFe2O4 powder produced by citrate auto-combustion synthesis. The auto-combusted powders were annealed at temperatures in the range 600 - 1000 o

Characterization of nanostructured TiO2:Ag films: structural and optical properties

TiO2:Ag nanocomposites have been prepared by sol-gel method with varying silver concentration. Different technological approaches are employed to study the formation of Ag nanoparticles in titanium dioxide matrix. The obtained thin films are either thermally treated at temperatures from 300 to 600oC or UV irradiated for 15 minutes between layer deposition. XRD and FTIR studies reveal that Ag is incorporated in TiO2 films as nanoparticles and no Ag oxide phases are detected. Optical characterization performed by UV-VIS spectroscopy confirms the formation of silver nanoparticles. The influence of thermal treatment and UV radiation on the optical and structural properties is studied.

Investigation of sol-gel yttrium doped ZnO thin films: structural and optical properties

Nanostructured metal oxide films are extensively studied due to their numerous applications such as optoelectronic devices, sensors. In this work, we report the Y-Zn-O nanostructured films prepared by sol-gel technology from sols with different concentration of yttrium precursor, followed by post-annealing treatment. The Y doped ZnO thin films have been deposited on Si and quartz substrates by spin coating method, then treated at temperatures ranging from 300-800oC. XRD analysis reveals modification of the film structure and phases in the doped ZnO films.

Characterization of sol - gel in doped ZnO films: Structural and optical properties

Sol-gel technology has been applied for preparation of ZnO:In films. The proposed facile approach allows obtaining a wide variety of indium doped zinc oxide films with different structural and optical behaviour. This work presents structural and optical studies of ZnO and ZnO:In nanostructures depending on In doping (four different concentrations) and on the thermal treatments in the range of 300-600°C. The structural analysis is performed by X-Ray diffraction (XRD). Vibrational properties have been characterized by FTIR spectroscopy. The effect of the indium introduction into ZnO reveals changing of optical properties compared to ZnO film. ZnO:In films manifest good transparency in visible spectral range.

Structural and Magnetic Properties and Preparation Techniques of Nanosized M-type Hexaferrite Powders

In recent years, the scientific efforts of a large number of research teams have been concentrating on developing, exploring and applying nanosized magnetic ferroxides. In this review, we consider the fundamental structural and magnetic characteristics of nanosized particles of barium hexaferrite. We discuss in some detail the most common techniques for preparation of nanosized ferroxide powders. Finally, we present original results on applying a promising chemical technique, namely, the single microemulsion technique, for the synthesis of barium hexaferrite powders consisting of homogeneous in shape and size particles.

Nanosized Barium Hexaferrite Powders Obtained by a Single Microemulsion Technique

Barium hexaferrite (BaFe12O19) powders of particle size of 130 and 180 nm were synthesized by a single microemulsion technique. The influence of the concentration of Ba2+ and Fe3+ metallic ions in the aqueous phase in the microemulsion system on the particle size distribution, crystallinity and magnetic properties of BaFe12O19 was studied. The coercive force and saturation magnetization of the sample obtained at a lower concentration of metallic cations in the aqueous phase were higher than those of the sample obtained at higher concentration.

Influence of the preparation methods on the structure and magnetic properties of nanosized Al-substituted barium hexaferrite powders

We report studies on the correlation between the method of preparation, microstructure and magnetic properties of nanosized monodomain Al-substituted barium hexaferrite (BaAlFe11O19) powders. The powders were obtained by the co-precipitation and single microemulsion methods. The particles in the samples had a size between 80 nm and 135 nm depending on the synthesis conditions. The value of the saturation magnetization Ms measured was very high, namely, 66.12 emu/g. The hysteresis loop was very narrow, with the coercivity Hc being 163 Oe, which indicated that the particles were in a near-superparamagnetic state.

Study of quasi-monophase Y-type hexaferrite Ba2Mg2Fe12O22 powder

We present the structural and magnetic properties of a multiferroic Ba2Mg2Fe12O22 hexaferrite composite containing a small amount of MgFe2O4. The composite material was obtained by auto-combustion synthesis and, alternatively, by co-precipitation. The Ba2Mg2Fe12O22 particles obtained by co-precipitation have an almost perfect hexagonal shape in contrast with those prepared by auto-combustion. Two magnetic phase transitions, responsible for the composites multiferroic properties, were observed, namely, at 183 K and 40 K for the material produced by auto-combustion, and at 196 K and 30 K for the sample prepared by co-precipitation. No magnetic phase transitions in these temperature ranges were observed for a MgFe2O4 sample, which shows that the magnesium ferrite does not affect the multiferroic properties of this type of multiferroic metarials.