Nataša Jović

Magnetic and structural studies of CoFe 2 O 4 nanoparticles suspended in an organic liquid

We present a study of magnetic and structural properties of CoFe2O4 nanoparticles suspended in an organic liquid. Transmission electron microscopy shows that the nanoparticles have a narrow size distribution of average particle size 5.9 ± 1.0 nm. X-ray diffraction shows that the particles are of cubic spinel crystal structure. Dynamic light scattering measurements reveal the existence of an organic shell around the CoFe2O4 nanoparticles with an average hydrodynamic diameter of 14.4 nm. Coercive magnetic field at T = 5K is found to be 11.8 kOe. Disappearance of the coercive field and remanent magnetization at about 170K suggests that the CoFe2O4 nanoparticles are superparamagnetic at higher temperatures which is confirmed by the room temperature Mossbauer spectrum analysis. Saturation magnetization of the nanoparticles of 80.8 emu/g(CoFe2O4) at 5K reaches the value detected in the bulk material and remains very high also at room temperature. The cobalt ferrite nanoparticle system synthesized in this work exhibits magnetic properties which are very suitable for various biomedical applications.

Synthesis and Characterization of Al, Y, Co and Cr Substituted Ultrafine Powder of NiFe2O4

The ultrafine spinel NiFe1.9M0.1O4 powders (M=Al, Y, Cr, Fe) were synthesized by thermal decomposition of appropriate mixtures of complex compounds with acetylacetone - (2,4 pentadione) ligands ([M(AA)x]) at 500 °C. Samples were annealed in the temperature range 600-1000 °C and the crystallization process was followed by XRD. The largest crystallite size and the highest crystallization rate are observed for NiFe1.9Al0.1O4, while the opposite was found for NiFe1.9Y0.1O4. Strain value in NiFe1.9Y0.1O4 changes sign at temperatures between 700-800 °C, while for NiFe1.9M0.1O4 (M=Al, Cr) it has a positive sign and reaches the maximum value at 700 °C. The crystal structure of the samples annealed at 1000 °C was refined using the Rietveld profile method. Cation substitution in Ni-ferrite changes its structural and microstructural parameters, and can also significantly influence other physical properties.

Influence of the Cation Distribution on the Physical Properties of the Diluted Magnetics Li1.33Ti1.67O4/Co2TiO4

Spinel samples of Li1.33xCo2-2xTi1+0.67xO4 crystallize in two space groups: Fd- 3 m for 0≤x≤0.40 and x=1, and P4332 for 0.50≤x≤0.875. In S.G. P4332 magnetic Co2+ ions occupy 8c sites (for x=0.75 and 0.875), or 8c, 4b and 12d sites (for x=0.50). In x=0.25 and 0.40 samples Co2+ occupy both 8a and 16d cation sites of the S.G. Fd- 3 m [1]. Observed differences in magnetic behaviour of the samples are induced by crystallographic distribution of Co2+. Possible paths for exchange interactions in S.G. P4332 were analysed. It was found that the superexchange is the dominant exchange mechanism where Co2+ (8c)-O(24e)-Co2+(12d) path was the most important one. On the basis of the results on crystallographic distribution we suggest x=0.50 sample as potential electrode material in Li ion rechargeable batteries.