Papers by Author: Darja Lisjak

Abstract: Stable suspensions of nanosized barium hexaferrite particles were prepared with the addition of surfactants. Hydrothermally prepared particles with sizes from 5 to 20 nm and commercial particles with sizes from 10 to 160 nm were used. The films with thicknesses from 1.5 to 9.5 μm were prepared with electrophoretic deposition in an external magnetic field. The orientation of the grains in the films was due to the magneto-crystalline anisotropy of the barium hexaferrite and was determined with X-ray diffraction analysis, scanning electron microscopy and magnetic measurements. The highest degree of orientation in the films with anisotropic magnetic behaviour was 90 %.

Abstract: Nanoparticles of barium hexaferrite were prepared by controlled hydrothermal synthesis at 280oC. During the synthesis, the composition of the precursor and the suspension concentration were controlled. The as-synthesized crystalline barium hexaferrite platelets of about 50 nm in length and 5 nm in thickness exhibited a saturation magnetization of 40 emu/g.

Abstract: The trend for integrating and miniaturizing electronic devices requires the co-firing of ferrites and Ag electrodes at 900°C. Here we report on compatibility studies using Z- and Y-type BaCo hexaferrites, which are interesting for microwave applications. Samples with compositions BaB3BCoB1.4BCuB0.6BFeB24BOB41 Band BaB2BCoB0.6BCuB1.4BFeB12BOB22 Bwere prepared with solid-state reactions at 1250°C and 1000°C, respectively. For compatibility tests, samples with additions of 0-25 wt.% of Ag were sintered at 900°C for 3h. The ceramics were characterized with X-ray powder diffraction and electron microscopy combined with energy-dispersive analysis. When co-sintered with Ag the hexaferrites decomposed to BaFeB12BOB19B and (Co,Cu)FeB2BOB4B or BaFeB2BOB4B. The incorporation of Ag in the spinel phase was also detected. The degree of decomposition increased with the amount of Ag and finally resulted in the complete disintegration of the samples with minimum 23 wt.% of Ag. The influence of the observed phase-composition changes on the electromagnetic properties and their dependence on frequency was evaluated.

Abstract: Magnetic nanoparticles are materials of great interest because of the remarkable fundamental properties exhibited by these materials as well as their technological potential in the area of biomedicine and other areas. The technologically useful properties of magnetic nanomaterials are not limited to their structural, chemical or mechanical behaviour, but also involve the phenomena that arise from their finite size and the surface effects that dominate the magnetic behaviour of individual nanoparticles. New techniques that have been developed recently have permitted researchers to produce larger quantities of nanomaterials and characterize them better. Here, some of the most promising procedures are reported, including techniques based on hydrothermal syntheses, sol-gel syntheses, co-precipitation syntheses, mechanochemical syntheses, sonochemical syntheses, spray pyrolysis and microemulsion-assisted syntheses.