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Magnetite ([Fe.sub.3][O.sub.4]) nanoparticles with very narrow particle size distribution can be obtained by decomposition of an organometallic compound in the presence of oleic acid. It has been shown that the carboxylic acid catalyzes the reaction leading to decreased decomposition temperatures and, consequently, as the surfactant concentration increases, smaller particles are formed. Precursors such as Fe[(CO).sub.5], iron acetylacetonate, and iron-oleate complexes, previously formed from an iron salt, have been used for the preparation of magnetite particles. Although the particles are magnetite in all cases, the size, shape, and distribution of nanoparticles differ depending on the precursor and consequently the samples show different magnetic behavior. Besides, a different mechanism of formation of the nanoparticles is expected and related to the decomposition rate of the precursor. Index Terms--Capping ligands, iron oxide, magnetic liquids, magnetic nanoparticles, magnetite, organometallic decomposition.

The surface spin canting studies for high quality magnetite nanoparticles in terms of size and shape uniformity prepared by thermal decomposition of organic precursors in organic media and in the presence of oleic acid is presented. The high synthesis temperature and the presence of oleic acid molecules covalently bonded at the particle surface which accounted for the lack of spin canting in particles prepared by thermal decomposition justified the high saturation magnetization and low coercivity at low temperature.

Abstract: Synthesis of magnetically separable photocatalytic active composite γ-Fe2O3@TiO2 is the main objective of this work. In the first step, maghemite nanoparticles were prepared by a precipitation method and consequently covered by the citric acid in order to adjust the zeta-potential of the particle surface. The magnetic carrier was enfolded by TiO2 via heterogeneous precipitation of TiOSO4 using urea as a precipitation agent. The procedure was designed to minimize the production costs in order to be easily transferred into the industry scale conserving the high quality of the photoactive product. Nontoxic element oxides were used because of the ecological acceptance. Various methods were employed to characterize and study the intermediate (magnetic nanoparticles) and final materials (TiO2-maghemite composite), respectively. Moreover, the influence of the subsequent annealing on the structure, phase composition and properties of the products is discussed. [Copyright &y& Elsevier]

Abstract: Collective magnetic behavior of CoFe2O4 nanoparticles with diameters of 76, 16, 15 and 8nm, respectively, prepared by different chemical methods has been investigated. Particle composition, size and structure have been characterized by inductive coupled plasma (ICP), transmission electron microscopy (TEM) and powder X-ray diffraction (PXRD). Basic magnetic properties have been determined from the temperature dependence of magnetization and magnetization isotherms measurements. The three samples exhibit characteristic of a superparamagnetic system with the presence of strong interparticle interactions. Magnetic relaxation phenomena have been examined via frequency-dependent ac susceptibility measurements and aging and memory effect experiments. For the particles coated with oleic acid, it has been demonstrated that the sample reveals all attributes of a super-spin glass (SSG) system with strong interparticle interactions. [Copyright &y& Elsevier]